In the philosophy of mind, innatism is the view that the mind is born with already-formed ideas, knowledge, and beliefs. The opposing doctrine, that the mind is a tabula rasa (blank slate) at birth and all knowledge is gained from experience and the senses, is called empiricism.
Innatism and nativism are generally synonymous terms
referring to the notion of preexisting ideas in the mind. However, more
specifically, innatism refers to the philosophy of Descartes, who assumed that God or a similar being or process placed innate ideas and principles in the human mind. The innatist principles in this regard may overlap with similar concepts such as natural order and state of nature, in philosophy.
Nativism represents an adaptation of this, grounded in the fields of genetics, cognitive psychology, and psycholinguistics. Nativists hold that innate beliefs are in some way genetically programmed in our mind—they are the phenotypes of certain genotypes
that all humans share in common. Nativism is a modern view rooted in
innatism. The advocates of nativism are mainly philosophers who also
work in the field of cognitive psychology or psycholinguistics: most notably Noam Chomsky and Jerry Fodor (although the latter adopted a more critical attitude toward nativism in his later writings).The nativist's general objection against empiricism is still the same as was raised by the rationalists; the human mind of a newborn child is not a tabula rasa but is equipped with an inborn structure.
History
Although
individual human beings vary in many ways (culturally, ethnically,
linguistically, and so on), innate ideas are the same for everyone
everywhere. For example, the philosopher René Descartes theorized that knowledge of God is innate in everybody. Philosophers such as Descartes and Plato were rationalists. Other philosophers, most notably the empiricists, were critical of innate ideas and denied they existed.
The debate over innate ideas is central to the conflict between
rationalists (who believe certain ideas exist independently of
experience) and empiricists (who believe knowledge is derived from
experience).
Many believe the German philosopher Immanuel Kant synthesized these two early modern traditions in his philosophical thought.
Plato
Plato
argues that if there are certain concepts that we know to be true but
did not learn from experience, then it must be because we have an innate
knowledge of it and that this knowledge must have been gained before
birth. In Plato's Meno, he recalls a situation where his mentor Socrates
questioned a slave boy about geometry. Though the slave boy had no
previous experience with geometry, he was able to answer correctly.
Plato reasoned that this was possible because Socrates' questions
sparked the innate knowledge of math the boy had from birth.
Descartes
Descartes
conveys the idea that innate knowledge or ideas is something inborn
such as one would say, that a certain disease might be 'innate' to
signify that a person might be at risk of contracting such a disease. He
suggests that something that is 'innate' is effectively present from
birth and while it may not reveal itself then, is more than likely to
present itself later in life. Descartes’ comparison of innate knowledge
to an innate disease, whose symptoms may show up only later in life,
unless prohibited by a factor like age or puberty, suggests that if an
event occurs prohibiting someone from exhibiting an innate behaviour or
knowledge, it doesn't mean the knowledge did not exist at all but rather
it wasn't expressed – they were not able to acquire that knowledge. In
other words, innate beliefs, ideas and knowledge require experiences to
be triggered or they may never be expressed. Experiences are not the
source of knowledge as proposed by John Locke, but catalysts to the
uncovering of knowledge.
Gottfried Wilhelm Leibniz
Gottfried Wilhelm Leibniz suggested that we are born with certain innate ideas, the most identifiable of these being mathematical truisms. The idea that 1 + 1 = 2 is evident to us without the necessity for empirical evidence.
Leibniz argues that empiricism can show us show that concepts are true
in the present; the observation of one apple and then another in one
instance, and in that instance only, leads to the conclusion that one
and another equals two. However, the suggestion that one and another
will always equal two requires an innate idea, as that would be a
suggestion of things unwitnessed.
Leibniz called such concepts as mathematical truisms "necessary
truths". Another example of such may be the phrase, "What is, is" or "It
is impossible for the same thing to be and not to be". Leibniz argues
that such truisms are universally assented to (acknowledged by all to be
true); this being the case, it must be due to their status as innate
ideas. Often some ideas are acknowledged as necessarily true but are not
universally assented to. Leibniz would suggest that this is simply
because the person in question has not become aware of the innate idea,
not because they do not possess it. Leibniz argues that empirical
evidence can serve to bring to the surface certain principles that are
already innately embedded in our minds. This is similar to needing to
hear only the first few notes to recall the rest of the melody.
John Locke
The main antagonist to the concept of innate ideas is John Locke,
a contemporary of Leibniz. Locke argued that the mind is in fact devoid
of all knowledge or ideas at birth; it is a blank sheet or tabula rasa.
He argued that all our ideas are constructed in the mind via a process
of constant composition and decomposition of the input that we receive
through our senses.
Locke, in An Essay Concerning Human Understanding,
suggests that the concept of universal assent in fact proves nothing,
except perhaps that everyone is in agreement; in short universal assent
proves that there is universal assent and nothing else. Moreover, Locke
goes on to suggest that in fact there is no universal assent.
Even a phrase such as "What is, is" is not universally assented to;
infants and severely mentally disabled adults do not generally
acknowledge this truism.
Locke also attacks the idea that an innate idea can be imprinted on the
mind without the owner realizing it. For Locke, such reasoning would
allow one to conclude the absurd: "All the Truths a Man ever comes to
know, will, by this account, be, every one of them, innate." To return to the musical analogy, we may not be able to recall the
entire melody until we hear the first few notes, but we were aware of
the fact that we knew the melody and that upon hearing the first few
notes we would be able to recall the rest.
Locke ends his attack upon innate ideas by suggesting that the mind is a tabula rasa or "blank slate", and that all ideas come from experience; all our knowledge is founded in sensory experience.
Essentially, the same knowledge thought to be a priori by
Leibniz is, according to Locke, the result of empirical knowledge, which
has a lost origin [been forgotten] in respect to the inquirer. However,
the inquirer is not cognizant of this fact; thus, he experiences what
he believes to be a priori knowledge.
The theory of innate knowledge is excessive. Even innatists
accept that most of our knowledge is learned through experience, but if
that can be extended to account for all knowledge, we learn color
through seeing it, so therefore, there is no need for a theory about an
innate understanding of color.
No ideas are universally held. Do we all possess the idea of God? Do
we all believe in justice and beauty? Do we all understand the law of
identity? If not, it may not be the case that we have acquired these
ideas through impressions/experience/social interaction.
Even if there are some universally agreed statements, it is just the
ability of the human brain to organize learned ideas/words, that is,
innate. An "ability to organize" is not the same as "possessing
propositional knowledge" (e.g., a computer with no saved files has all
the operations programmed in but has an empty memory).
Contemporary approaches
Linguistics
In his Meno,
Plato raises an important epistemological quandary: How is it that we
have certain ideas that are not conclusively derivable from our
environments? Noam Chomsky
has taken this problem as a philosophical framework for the scientific
inquiry into innatism. His linguistic theory, which derives from 18th
century classical-liberal thinkers such as Wilhelm von Humboldt,
attempts to explain in cognitive terms how we can develop knowledge of
systems which are said, by supporters of innatism, to be too rich and
complex to be derived from our environment. One such example is our
linguistic faculty. Our linguistic systems contain a systemic complexity
which supposedly could not be empirically derived: the environment
seems too poor, variable and indeterminate,
according to Chomsky, to explain the extraordinary ability to learn
complex concepts possessed by very young children. Essentially, their
accurate grammatical knowledge cannot have originated from their
experiences as their experiences are not adequate. It follows that humans must be born with a universal innate grammar,
which is determinate and has a highly organized directive component,
and enables the language learner to ascertain and categorize language
heard into a system. Chomsky states that the ability to learn how to
properly construct sentences or know which sentences are grammatically
incorrect is an ability gained from innate knowledge. Noam Chomsky cites as evidence for this theory, the apparent
invariability, according to his views, of human languages at a
fundamental level. In this way, linguistics may provide a window into
the human mind, and establish scientific theories of innateness which
otherwise would remain merely speculative.
One implication of Noam Chomsky's innatism, if correct, is that
at least a part of human knowledge consists in cognitive
predispositions, which are triggered and developed by the environment,
but not determined by it. Chomsky suggests that we can look at how a
belief is acquired as an input-output situation. He supports the
doctrine of innatism as he states that human beliefs gathered from
sensory experience are much richer and complex than the experience
itself. He asserts that the extra information gathered is from the mind
itself as it cannot solely be from experiences. Humans derive excess
amount of information from their environment so some of that information
must be pre-determined.
There are two types of interplanetary contamination:
Forward contamination is the transfer of life and other forms of contamination from Earth to another celestial body.
Back contamination is the introduction of extraterrestrial organisms and other forms of contamination into Earth's biosphere.
It also covers infection of humans and human habitats in space and on
other celestial bodies by extraterrestrial organisms, if such organisms
exist.
The main focus is on microbial life and on potentially invasive species.
Non-biological forms of contamination have also been considered,
including contamination of sensitive deposits (such as lunar polar ice
deposits) of scientific interest. In the case of back contamination, multicellular life is thought
unlikely but has not been ruled out. In the case of forward
contamination, contamination by multicellular life (e.g. lichens) is
unlikely to occur for robotic missions, but it becomes a consideration
in crewed missions to Mars.
Current space missions are governed by the Outer Space Treaty and the COSPAR guidelines for planetary protection. Forward contamination is prevented primarily by sterilizing the spacecraft. In the case of sample-return missions,
the aim of the mission is to return extraterrestrial samples to Earth,
and sterilization of the samples would make them of much less interest.
So, back contamination would be prevented mainly by containment, and
breaking the chain of contact between the planet of origin and Earth. It
would also require quarantine procedures for the materials and for anyone who comes into contact with them.
Overview
Most of the Solar System
appears hostile to life as we know it. No extraterrestrial life has
ever been discovered. But if extraterrestrial life exists, it may be
vulnerable to interplanetary contamination by foreign microorganisms.
Some extremophiles
may be able to survive space travel to another planet, and foreign life
could possibly be introduced by spacecraft from Earth. If possible,
some believe this poses scientific and ethical concerns.
Locations within the Solar System where life might exist today include the oceans of liquid water beneath the icy surface of Europa, Enceladus,
and Titan (its surface has oceans of liquid ethane / methane, but it may also have liquid water below the surface and ice volcanoes).
There are multiple consequences for both forward- and
back-contamination. If a planet becomes contaminated with Earth life, it
might then be difficult to tell whether any lifeforms discovered
originated there or came from Earth. Furthermore, the organic chemicals produced by the introduced life would confuse sensitive searches for biosignatures
of living or ancient native life. The same applies to other more
complex biosignatures. Life on other planets could have a common origin
with Earth life, since in the early Solar System there was much exchange
of material between the planets which could have transferred life as
well. If so, it might be based on nucleic acids too (RNA or DNA).
The majority of the species isolated are not well understood or
characterized and cannot be cultured in labs, and are known only from
DNA fragments obtained with swabs. On a contaminated planet, it might be difficult to distinguish the DNA
of extraterrestrial life from the DNA of life brought to the planet by
the exploring. Most species of microorganisms on Earth are not yet well
understood or DNA sequenced. This particularly applies to the
unculturable archaea,
and so are difficult to study. This can be either because they depend
on the presence of other microorganisms, are slow growing, or depend on
other conditions not yet understood. In typical habitats, 99% of microorganisms are not culturable. Introduced Earth life could contaminate resources of value for future human missions, such as water.
Invasive species could outcompete native life or consume it, if there is life on the planet. However, the experience on earth shows that species moved from one
continent to another may be able to out compete the native life adapted
to that continent. Additionally, evolutionary processes on Earth might have developed
biological pathways different from extraterrestrial organisms, and so
may be able to outcompete it. The same is also possible the other way
around for contamination introduced to Earth's biosphere.
In addition to science research concerns, there are also attempts
to raise ethical and moral concerns regarding intentional or
unintentional interplanetary transport of life.
Evidence for possible habitats outside Earth
Enceladus and Europa show the best evidence for current habitats, mainly due to the possibility of their hosting liquid water and organic compounds.
There is ample evidence to suggest that Mars once offered habitable conditions for microbial life.It is therefore possible that microbial life may have existed on Mars, although no evidence has been found.
It is thought that many bacterial spores (endospores) from Earth were transported on Mars spacecraft. Some may be protected within Martian rovers and landers on the shallow surface of the planet. In that sense, Mars may have already been contaminated.
Certain lichens from the arctic permafrost are able to photosynthesize
and grow in the absence of any liquid water, simply by using the
humidity from the atmosphere. They are also highly tolerant of UV radiation, using melanin and other more specialized chemicals to protect their cells.
Although numerous studies point to resistance to some of Mars
conditions, they do so separately, and none have considered the full
range of Martian surface conditions, including temperature, pressure,
atmospheric composition, radiation, humidity, oxidizing regolith, and
others, all at the same time and in combination. Laboratory simulations show that whenever multiple lethal factors are combined, the survival rates plummet quickly.
Other studies have suggested the potential for life to survive using deliquescing salts.
These, similarly to the lichens, use the humidity of the atmosphere. If
the mixture of salts is right, the organisms may obtain liquid water at
times of high atmospheric humidity, with salts capturing enough to be
capable of supporting life.
Research published in July 2017 shows that when irradiated with a simulated Martian UV flux, perchlorates become even more lethal to bacteria (bactericide effect). Even dormant spores lost viability within minutes. In addition, two other compounds of the Martian surface, iron oxides and hydrogen peroxide,
act in synergy with irradiated perchlorates to cause a 10.8-fold
increase in cell death when compared to cells exposed to UV radiation
after 60 seconds of exposure. It was also found that abraded silicates (quartz and basalt) lead to the formation of toxic reactive oxygen species. The researchers concluded that "the surface of Mars is lethal to
vegetative cells and renders much of the surface and near-surface
regions uninhabitable." This research demonstrates that the present-day surface is more uninhabitable than previously thought, and reinforces the notion to inspect at least a few meters into the
ground to ensure the levels of radiation would be relatively low.
Enceladus
The Cassini spacecraftdirectly sampled the plumes escaping from Enceladus.
Measured data indicates that these geysers are made primarily of salt
rich particles with an 'ocean-like' composition, which is thought to
originate from a subsurface ocean of liquid saltwater, rather than from the moon's icy surface. Data from the geyser flythroughs also indicate the presence of organic
chemicals in the plumes. Heat scans of Enceladus's surface also indicate
higher temperatures around the fissures where the geysers originate,
with temperatures reaching −93 °C (−135 °F), which is 115 °C (207 °F)
warmer than the surrounding surface regions.
Europa
Europa has much indirect evidence for its sub-surface ocean. Models of how Europa is affected by tidal heating
require a subsurface layer of liquid water in order to accurately
reproduce the linear fracturing of the surface. Indeed, observations by
the Galileo spacecraft of how Europa's magnetic field interacts with Jupiter's field strengthens the case for a liquid, rather than solid, layer; an electrically conductive fluid deep within Europa would explain these results. Observations from the Hubble Space Telescope in December 2012 appear to show an ice plume spouting from Europa's surface, which would immensely strengthen the case for a liquid subsurface
ocean. As was the case for Enceladus, vapour geysers would allow for
easy sampling of the liquid layer. Unfortunately, there appears to be little evidence that geysering is a
frequent event on Europa due to the lack of water in the space near
Europa.
Forward contamination is prevented by sterilizing space probes
sent to sensitive areas of the Solar System. Missions are classified
depending on whether their destinations are of interest for the search
for life, and whether there is any chance that Earth life could
reproduce there.
NASA made these policies official with the issuing of Management Manual NMI-4-4-1, NASA Unmanned Spacecraft Decontamination Policy on September 9, 1963. Prior to NMI-4-4-1 the same sterilization requirements were required
on all outgoing spacecraft regardless of their target. Difficulties in
the sterilization of Ranger probes sent to the Moon are the primary
reasons for NASA's change to a target-by-target basis in assessing the
likelihood forward contamination.
Some destinations such as Mercury
need no precautions at all. Others such as the Moon require
documentation but nothing more, while destinations such as Mars require
sterilization of the rovers sent there.
Back contamination would be prevented by containment or
quarantine. However, there have been no sample-returns thought to have
any possibility of a back contamination risk since the Apollo missions. The Apollo regulations have been rescinded and new regulations have yet to be developed. See suggested precautions for sample-returns.
Crewed spacecraft
Crewed spacecraft
are of particular concern for interplanetary contamination because of
the impossibility to sterilize a human to the same level as a robotic
spacecraft. Therefore, the chance of forwarding contamination is higher
than for a robotic mission. Humans are typically host to a hundred trillion microorganisms in ten thousand species in the human microbiome
which cannot be removed while preserving the life of the human.
Containment seems the only option, but effective containment to the same
standard as a robotic rover appears difficult to achieve with
present-day technology. In particular, adequate containment in the event
of a hard landing is a major challenge.
Human explorers may be potential carriers back to Earth of microorganisms acquired on Mars, if such microorganisms exist. Another issue is the contamination of the water supply by Earth
microorganisms shed by humans in their stools, skin and breath, which
could have a direct effect on the long-term human colonization of Mars.
Historical examples of measures taken to prevent planetary
contamination of the moon include the inclusion of an anti-bacterial
filter in the Apollo Lunar Module, from Apollo 13
and onward. This was placed on the cabin relief valve in order to
prevent contaminants from the cabin being released into the lunar
environment during the depressurization of the crew compartment, prior
to EVA.
The Moon
The Apollo 11 missions incited public concern about the possibility of microbes on the Moon, creating fears about a plague being brought to Earth when the astronauts returned. NASA received thousands of letters from Americans concerned with the potential for back contamination.
As a testbed
The Moon
has been suggested as a testbed for new technology to protect sites in
the Solar System, and astronauts, from forward and back contamination.
Currently, the Moon has no contamination restrictions because it is
considered to be "not of interest" for prebiotic chemistry and origins of life. Analysis of the contamination left by the Apollo program astronauts could also yield useful ground truth for planetary protection models.
Non-contaminating exploration methods
Telerobotics exploration on Mars and Earth
One of the most reliable ways to reduce the risk of forward and back
contamination during visits to extraterrestrial bodies is to use only robotic spacecraft. Humans in close orbit around the target planet could control equipment
on the surface in real time via telepresence, so bringing many of the
benefits of a surface mission, without its associated increased forward
and back contamination risks.
Back contamination issues
Since
the Moon is now generally considered to be free from life, the most
likely source of contamination would be from Mars during either a Mars sample-return mission or as a result of a crewed mission to Mars.
The possibility of new human pathogens, or environmental disruption due
to back contamination, is considered to be of extremely low probability
but cannot yet be ruled out.
NASA and ESA are actively developing a Mars Sample Return Program
to return samples collected by the Perseverance Rover to Earth. The
European Space Foundation report cites many advantages of a Mars
sample-return. In particular, it would permit extensive analyses on
Earth, without the size and weight constraints for instruments sent to
Mars on rovers. These analyses could also be carried out without the
communication delays for experiments carried out by Martian rovers. It
would also make it possible to repeat experiments in multiple
laboratories with different instruments to confirm key results.
Carl Sagan was first to publicise back contamination issues that might follow from a Mars sample-return. In Cosmic Connection (1973) he wrote:
Precisely because Mars is an
environment of great potential biological interest, it is possible that
on Mars there are pathogens, organisms which, if transported to the
terrestrial environment, might do enormous biological damage.
Later in Cosmos (1980) Carl Sagan wrote:
Perhaps Martian samples can be
safely returned to Earth. But I would want to be very sure before
considering a returned-sample mission.
NASA and ESA views are similar. The findings were that with
present-day technology, Martian samples can be safely returned to Earth
provided the right precautions are taken.
Suggested precautions for sample-returns
NASA
has already had experience with returning samples thought to represent a
low back contamination risk when samples were returned for the first
time by Apollo 11.
At the time, it was thought that there was a low probability of life on
the Moon, so the requirements were not very stringent. The precautions
taken then were inadequate by current standards, however. The
regulations used then have been rescinded, and new regulations and
approaches for a sample-return would be needed.
Chain of contact
A
sample-return mission would be designed to break the chain of contact
between Mars and the exterior of the sample container, for instance, by
sealing the returned container inside another larger container in the
vacuum of space before it returns to Earth. In order to eliminate the risk of parachute failure, the capsule could
fall at terminal velocity and the impact would be cushioned by the
capsule's thermal protection system. The sample container would be
designed to withstand the force of the impact.
Receiving facility
Working inside a BSL-4 laboratory with air hoses providing positive air pressure to their suits
To receive, analyze and curate extraterrestrial soil samples, NASA
has proposed to build a biohazard containment facility, tentatively
known as the Mars Sample Return Receiving Facility (MSRRF). This future facility must be rated biohazard level 4 (BSL-4). While existing BSL-4 facilities deal primarily with fairly well-known
organisms, a BSL-4 facility focused on extraterrestrial samples must
pre-plan the systems carefully while being mindful that there will be
unforeseen issues during sample evaluation and curation that will
require independent thinking and solutions.
The facility's systems must be able to contain unknown
biohazards, as the sizes of any putative Martian microorganisms are
unknown. In consideration of this, additional requirements were
proposed. Ideally it should filter particles of 0.01 μm or larger, and
release of a particle 0.05 μm or larger is unacceptable under any
circumstance.
The reason for this extremely small size limit of 0.01 μm is for consideration of gene transfer agents (GTAs) which are virus-like particles that are produced by some microorganisms that package random segments of DNA capable of horizontal gene transfer. These randomly incorporate segments of the host genome and can transfer
them to other evolutionarily distant hosts, and do that without killing
the new host. In this way many archaea and bacteria can swap DNA with
each other. This raises the possibility that Martian life, if it has a
common origin with Earth life in the distant past, could swap DNA with
Earth microorganisms in the same way. In one experiment reported in 2010, researchers left GTAs (DNA
conferring antibiotic resistance) and marine bacteria overnight in
natural conditions and found that by the next day up to 47% of the
bacteria had incorporated the genetic material from the GTAs. Another reason for the 0.05 μm limit is because of the discovery of ultramicrobacteria as small as 0.2 μm across.
The BSL-4 containment facility must also double as a cleanroom
to preserve the scientific value of the samples. A challenge is that,
while it is relatively easy to simply contain the samples once returned
to Earth, researchers would also want to remove parts of the sample and
perform analyses. During all these handling procedures, the samples
would need to be protected from Earthly contamination. A cleanroom
is normally kept at a higher pressure than the external environment to
keep contaminants out, while a biohazard laboratory is kept at a lower
pressure to keep the biohazards in. This would require
compartmentalizing the specialized rooms in order to combine them in a
single building. Solutions suggested include a triple walled containment
facility, and extensive robotic handling of the samples.
The facility would be expected to take 7 to 10 years from design to completion, and an additional two years recommended for the staff to become accustomed to the facilities.
Dissenting views on back contamination
Robert Zubrin, from the Mars Society,
maintains that the risk of back contamination is negligible. He
supports this using an argument based on the possibility of transfer of
life from Earth to Mars on meteorites.
Legal process of approval for Mars sample-return
Margaret Race has examined in detail the legal process of approval for a MSR. She found that under the National Environmental Policy Act (NEPA)
(which did not exist in the Apollo era), a formal environment impact
statement is likely to be required, and public hearings during which all
the issues would be aired openly. This process is likely to take up to
several years to complete.
During this process, she found, the full range of worst accident
scenarios, impact, and project alternatives would be played out in the
public arena. Other agencies such as the Environment Protection Agency,
Occupational Health and Safety Administration, etc., might also get
involved in the decision-making process.
The laws on quarantine would also need to be clarified as the
regulations for the Apollo program were rescinded. In the Apollo era,
NASA delayed announcement of its quarantine regulations until the day
Apollo was launched, bypassing the requirement for public debate -
something that would likely not be tolerated today.
It is also probable that the presidential directive NSC-25 would
apply, requiring a review of large scale alleged effects on the
environment to be carried out subsequent to other domestic reviews and
through a long process, leading eventually to presidential approval of
the launch.
Apart from those domestic legal hurdles, there would be numerous
international regulations and treaties to be negotiated in the case of a
Mars sample-return, especially those relating to environmental
protection and health. Race concluded that the public of necessity has a
significant role to play in the development of the policies governing
Mars sample-return.
Alternatives to sample-returns
Several
exobiologists have suggested that a Mars sample-return is not necessary
at this stage, and that it is better to focus more on in situ studies
on the surface first. Although it is not their main motivation, this
approach of course also eliminates back contamination risks.
Some of these exobiologists advocate more in situ studies
followed by a sample-return in the near future. Others go as far as to
advocate in situ study instead of a sample-return at the present state
of understanding of Mars.
Their reasoning is that life on Mars is likely to be hard to
find. Any present day life is likely to be sparse and occur in only a
few niche habitats. Past life is likely to be degraded by cosmic
radiation over geological time periods if exposed in the top few meters
of the Mars surface. Also, only certain special deposits of salts or
clays on Mars would have the capability to preserve organics for
billions of years. So, they argue, there is a high risk that a Mars
sample-return at our current stage of understanding would return samples
that are no more conclusive about the origins of life on Mars or
present day life than the Martian meteorite samples we already have.
Another consideration is the difficulty of keeping the sample
completely free from Earth life contamination during the return journey
and during handling procedures on Earth. This might make it hard to show
conclusively that any biosignatures detected does not result from
contamination of the samples.
Instead they advocate sending more sensitive instruments on Mars
surface rovers. These could examine many different rocks and soil types,
and search for biosignatures on the surface and so examine a wide range
of materials which could not all be returned to Earth with current
technology at reasonable cost.
A sample-return to Earth would then be considered at a later
stage, once we have a reasonably thorough understanding of conditions on
Mars, and possibly have already detected life there, either current or
past life, through biosignatures and other in situ analyses.
Instruments under development for in situ analyses
NASA
Marshall Space Flight Center is leading a research effort to develop a
Miniaturized Variable Pressure Scanning Electron Microscope (MVP-SEM)
for future lunar and Martian missions.[77]
Several teams, including Jonathan Rothberg, and J. Craig Venter,
are separately developing solutions for sequencing alien DNA directly
on the Martian surface itself.
Levin is working on updated versions of the Labeled Release
instrument flown on Viking. For instance versions that rely on detecting
chirality. This is of special interest because it can enable detection
of life even if it is not based on standard life chemistry.
The Urey Mars Organic and Oxidant Detector instrument for detection
of biosignatures has been descoped, but was due to be flown on ExoMars in 2018. It is designed with much higher levels of sensitivity for biosignatures than any previous instruments.
Study and analyses from orbit
During
the “Exploration Telerobotics Symposium" in 2012, experts on
telerobotics from industry, NASA, and academics met to discuss
telerobotics and its applications to space exploration. Amongst other
issues, particular attention was given to Mars missions and a Mars
sample-return.
They came to the conclusion that telerobotic approaches could
permit direct study of the samples on the Mars surface via telepresence
from Mars orbit, permitting rapid exploration and use of human cognition
to take advantage of chance discoveries and feedback from the results
obtained.
They found that telepresence exploration of Mars has many
advantages. The astronauts have near real-time control of the robots,
and can respond immediately to discoveries. It also prevents
contamination both ways and has mobility benefits as well.
Finally, return of the sample to orbit has the advantage that it
permits analysis of the sample without delay, to detect volatiles that
may be lost during a voyage home.
Telerobotics exploration of Mars
Similar methods could be used to directly explore other biologically sensitive moons such as Europa, Titan, or Enceladus, once human presence in the vicinity becomes possible.
In August 2019, scientists reported that a capsule containing tardigrades (a resilient microbial animal) in a cryptobiotic state may have survived for a while on the Moon after the April 2019 crash landing of Beresheet, a failed Israeli lunar lander.
Science of morality (also known as science of ethics or scientific ethics) may refer to various forms of ethical naturalism grounding morality and ethics in rational, empirical consideration of the natural world. It is sometimes framed as using the scientific approach to determine
what is right and wrong, in contrast to the widespread belief that
"science has nothing to say on the subject of human values".
Overview
Moral science may refer to the consideration of what is best for, and how to maximize the flourishing of, either particular individuals or all conscious creatures. It has been proposed that "morality" can be appropriately defined on the basis of fundamental premises necessary for any
empirical, secular, or philosophical discussion and that societies can
use the methods of science to provide answers to moral questions.
The norms advocated by moral scientists (e.g. rights to abortion, euthanasia, and drug liberalization under certain circumstances) would be founded upon the shifting and growing collection of human understanding. Even with science's admitted degree of ignorance, and the various
semantic issues, moral scientists can meaningfully discuss things as
being almost certainly "better" or "worse" for promoting flourishing.
History
In philosophy
UtilitarianJeremy Bentham discussed some of the ways moral investigations are a science. He criticized deontological ethics
for failing to recognize that it needed to make the same presumptions
as his science of morality to really work – whilst pursuing rules that
were to be obeyed in every situation (something that worried Bentham).
W. V. O. Quine advocated naturalizing epistemology by looking to natural sciences like psychology for a full explanation of knowledge. His work contributed to a resurgence of moral naturalism in the last half of the 20th century. Paul Kurtz, who believes that the careful, secular pursuit of normative rules is vital to society, coined the term eupraxophy to refer to his approach to normative ethics. Steven Pinker, Sam Harris, and Peter Singer believe that we learn what is right and wrong through reason and empirical methodology.
Maria Ossowska used the methods of science to understand the origins of moral norms.
Maria Ossowska
thought that sociology was inextricably related to philosophical
reflections on morality, including normative ethics. She proposed that
science analyse: (a) existing social norms and their history, (b) the
psychology of morality, and the way that individuals interact with moral
matters and prescriptions, and (c) the sociology of morality.
In popular literature
The theory and methods of a normative science of morality are explicitly discussed in Joseph Daleiden's The Science of Morality: The Individual, Community, and Future Generations (1998). Daleiden's book, in contrast to Harris, extensively discusses the relevant philosophical literature. In The Moral Landscape: How Science Can Determine Human Values, Sam Harris's goal is to show how moral truth can be backed by "science", or more specifically, empirical knowledge, critical thinking, philosophy, but most controversially, the scientific method.
Our moral behavior, while more
complex than the social behavior of other animals, is similar in that it
represents our attempt to manage well in the existing social
ecology. ... from the perspective of neuroscience and brain evolution,
the routine rejection of scientific approaches to moral behavior based
on Hume's warning against deriving ought from is seems
unfortunate, especially as the warning is limited to deductive
inferences. ... The truth seems to be that values rooted in the
circuitry for caring—for well-being of self, offspring, mates, kin, and
others—shape social reasoning about many issues: conflict resolutions,
keeping the peace, defense, trade, resource distribution, and many other
aspects of social life in all its vast richness.
Daleiden and Leonard Carmichael warn that science is probabilistic, and that certainty is not possible. One should therefore expect that moral prescriptions will change as humans gain understanding.
In futurism
Transhumanist philosophers such as David Pearce and Mark Alan Walker have extensively discussed the ethical implications of future technologies. Walker coined the term "biohappiness" to describe the idea of directly manipulating the biological roots of happiness in order to increase it. Pearce argues that suffering could eventually be eradicated entirely, stating that: "It is predicted that the world's last unpleasant experience will be a precisely dateable event." Proposed technological methods of overcoming the hedonic treadmill include wireheading
(direct brain stimulation for uniform bliss), which undermines
motivation and evolutionary fitness; designer drugs, offering
sustainable well-being without side effects, though impractical for
lifelong reliance; and genetic engineering,
the most promising approach. Genetic recalibration through
hyperthymia-promoting genes could raise hedonic set-points, fostering
adaptive well-being, creativity, and productivity while maintaining
responsiveness to stimuli. While scientifically achievable, this
transformation requires careful ethical and societal considerations to
navigate its profound implications.
The science of morality may aim to discover the best ways to motivate
and shape individuals. Methods to accomplish this include instilling
explicit virtues, building character strengths, and forming mental associations.
These generally require some level of practical reason. James Rest
suggested that abstract reasoning is also a factor in making moral
judgements and emphasized that moral judgements alone do not predict moral
behaviour: “Moral judgement may be closely related to advocacy
behaviour, which in turn influences social institutions, which in turn
creates a system of norms and sanctions that influences people’s
behaviour.” Daleiden suggested that religions instill a practical sense of virtue
and justice, right and wrong. They also effectively use art and myths to
educate people about moral situations.
Role of government
Harris argues that moral science does not imply an "Orwellian
future" with "scientists at every door". Instead, Harris imagines data
about normative moral issues being shared in the same way as other
sciences (e.g. peer-reviewed journals on medicine).
Daleiden specifies that government, like any organization, should
have limited power. He says "centralization of power irrevocably in the
hands of one person or an elite has always ultimately led to great evil
for the human race. It was the novel experiment of democracy—a clear
break with tradition—that ended the long tradition of tyranny.” He is also explicit that government
should only use law to enforce the most basic, reasonable, proven and
widely supported moral norms. In other words, there are a great many
moral norms that should never be the task of the government to enforce.
One author has argued that to attain a society where people are motivated by conditioned self-interest, punishment must go hand-in-hand with reward. For instance, in this line of reasoning, prison remains necessary for
many perpetrators of crimes. This is so, even if libertarian free will
is false. This is because punishment can still serve its purposes: it
deters others from committing their own crimes, educates and reminds
everyone about what the society stands for, incapacitates the criminal
from doing more harm, goes some way to relieving or repaying the victim,
and corrects the criminal (also see recidivism). This author argues that, at least, any prison system should
be pursuing those goals, and that it is an empirical question as to
what sorts of punishment realize these goals most effectively, and how
well various prison systems actually serve these purposes.
The brain areas that are consistently involved when humans reason about moral issues have been investigated. The neural network underlying moral decisions overlaps with the
network pertaining to representing others' intentions (i.e., theory of
mind) and the network pertaining to representing others' (vicariously
experienced) emotional states (i.e., empathy). This supports the notion
that moral reasoning is related to both seeing things from other
persons’ points of view and to grasping others’ feelings. These results
provide evidence that the neural network underlying moral decisions is
probably domain-global (i.e., there might be no such things as a "moral
module" in the human brain) and might be dissociable into cognitive and
affective sub-systems.
An essential, shared component of moral judgment involves the
capacity to detect morally salient content within a given social
context. Recent research implicated the salience network in this initial
detection of moral content. The salience network responds to behaviourally salient events, and may be critical to modulate downstream default and frontal control
network interactions in the service of complex moral reasoning and
decision-making processes. This suggest that moral cognition involves
both bottom-up and top-down attentional processes, mediated by discrete
large-scale brain networks and their interactions.
In universities
Moral sciences is offered at the degree level at Ghent University (as "an integrated empirical and philosophical study of values, norms and world views")
Other implications
Daleiden
provides examples of how science can use empirical evidence to assess
the effect that specific behaviours can have on the well-being of
individuals and society with regard to various moral issues. He argues
that science supports decriminalization and regulation of drugs,
euthanasia under some circumstances, and the permission of sexual
behaviours that are not tolerated in some cultures (he cites homosexuality as an example). Daleiden further argues that in seeking to reduce human suffering, abortion
should not only be permissible, but at times a moral obligation (as in
the case of a mother of a potential child who would face the probability
of much suffering). Like all moral claims in his book, however,
Daleiden is adamant that these decisions remain grounded in, and
contingent on empirical evidence.
The ideas of cultural relativity,
to Daleiden, do offer some lessons: investigators must be careful not
to judge a person's behaviour without understanding the environmental
context. An action may be necessary and more moral once we are aware of
circumstances. However, Daleiden emphasizes that this does not mean all ethical norms
or systems are equally effective at promoting flourishing and he often offers the equal treatment of women as a reliably superior norm, wherever it is practiced.
Criticisms
The
idea of a normative science of morality has met with many criticisms
from scientists and philosophers. Critics include physicist Sean M. Carroll, who argues that morality cannot be part of science. He and other critics cite the widely held "fact-value distinction",
that the scientific method cannot answer "moral" questions, although it
can describe the norms of different cultures. In contrast, moral
scientists defend the position that such a division between values and
scientific facts ("moral relativism") is not only arbitrary and
illusory, but impeding progress towards taking action against documented
cases of human rights violations in different cultures.
Stephen Jay Gould argued that science and religion occupy "non-overlapping magisteria".
To Gould, science is concerned with questions of fact and theory, but
not with meaning and morality – the magisteria of religion. In the same
vein, Edward Teller proposed that politics decides what is right, whereas science decides what is true.
During a discussion on the role that naturalism might play in professions like nursing,
the philosopher Trevor Hussey calls the popular view that science is
unconcerned with morality "too simplistic". Although his main focus in
the paper is naturalism in nursing, he goes on to explain that science
can, at very least, be interested in morality at a descriptive level. He
even briefly entertains the idea that morality could itself be a
scientific subject, writing that one might argue "... that moral
judgements are subject to the same kinds of rational, empirical
examination as the rest of the world: they are a subject for science –
although a difficult one. If this could be shown to be so, morality
would be contained within naturalism. However, I will not assume the
truth of moral realism here."
The metaphor "stream of consciousness" suggests how thoughts seem to flow through the consciousmind. Research studies have shown that humans only experience one mental event at a time, as a fast-moving mind-stream. The full range of thoughts one can be aware of forms the content of this "stream".
The term was coined by Alexander Bain in 1855, when he wrote in The Senses and the Intellect, "The concurrence of Sensations
in one common stream of consciousness (on the same cerebral highway)
enables those of different senses to be associated as readily as the
sensations of the same sense". But the man who popularized it is commonly credited instead: William James, often considered the father of American psychology, used it in 1890 in The Principles of Psychology.
Early Buddhist scriptures describe the "stream of consciousness" (Pali; viññāna-sota) where it is referred to as the Mindstream. The practice of mindfulness, which is about being aware moment-to-moment of one's subjective conscious experience, aid one to directly experience the "stream of consciousness" and to gradually cultivate self-knowledge and wisdom.
Buddhist teachings describe the continuous flow of the "stream of
mental and material events" as including sensory experiences (i.e.,
seeing, hearing, smelling, tasting, touch sensations, or a thought
relating to the past, present or future) as well as various mental
events that are generated, namely, feelings, perceptions and
intentions/behaviour. These mental events are also described as being influenced by other factors such as attachments and past conditioning. Further, the moment-by-moment manifestation of the "stream of
consciousness" is described as being affected by physical laws,
biological laws, psychological laws, volitional laws, and universal
laws.
"The logical significance of the law of Reason and Consequent
lies in this, – That in virtue of it, thought is constituted into a
series of acts all indissolubly connected; each necessarily inferring
the other" (Hamilton 1860:61-62).
In this context the words "necessarily infer" are synonymous with "imply". In further discussion Hamilton identified "the law" with modus ponens; thus the act of "necessarily infer" detaches the consequent for
purposes of becoming the (next) antecedent in a "chain" of connected
inferences.
William James asserts the notion as follows:
"Consciousness, then, does not appear to itself chopped up in
bits. Such words as 'chain' or 'train' do not describe it fitly as it
presents itself in the first instance. It is nothing jointed; it flows. A
'river' or a 'stream' are the metaphors by which it is most naturally
described. In talking of it hereafter let us call it the stream of thought, of consciousness, or of subjective life. (James 1890:239)
He was enormously skeptical about using introspection
as a technique to understand the stream of consciousness. "The attempt
at introspective analysis in these cases is in fact like seizing a
spinning top to catch its motion, or trying to turn up the gas quickly
enough to see how the darkness looks." However, the epistemological separation of two levels of analyses
appears to be important in order to systematically understand the
"stream of consciousness."
Conceptually understanding what is meant by the "present moment,"
"the past" and "the future" can aid one to systematically understand
the "stream of consciousness."
Criticism
Susan Blackmore
challenged the concept of stream of consciousness. "When I say that
consciousness is an illusion I do not mean that consciousness does not
exist. I mean that consciousness is not what it appears to be. If it
seems to be a continuous stream of rich and detailed experiences,
happening one after the other to a conscious person, this is the
illusion." However, she also says that a good way to observe the "stream
of consciousness" may be to calm the mind in meditation. The criticism
is based on the stream of perception data from the senses rather than
about consciousness itself. Also, it is not explained the reason why
some things are conscious at all. Suggestions have also been made regarding the importance of separating
"two levels of analyses" when attempting to understand the "stream of
consciousness".
Baars is in agreement with these points. The continuity of the
"stream of consciousness" may in fact be illusory, just as the
continuity of a movie is illusory. Nevertheless, the seriality of
mutually incompatible conscious events is well supported by objective
research over some two centuries of experimental work. A simple
illustration would be to try to be conscious of two interpretations of
an ambiguous figure or word at the same time. When timing is precisely
controlled, as in the case of the audio and video tracks of the same
movie, seriality appears to be compulsory for potentially conscious
events presented within the same 100 ms interval.
J. W. Dalton has criticized the global workspace theory on the grounds that it provides, at best, an account of the cognitive function of consciousness, and fails even to address the deeper problem of its nature, of what consciousness is, and of how any mental process whatsoever can be conscious: the so-called "hard problem of consciousness". Avshalom Elitzur
has argued, however, "While this hypothesis does not address the 'hard
problem', namely, the very nature of consciousness, it constrains any
theory that attempts to do so and provides important insights into the
relation between consciousness and cognition.", as much as any
consciousness theory is constrained by the natural brain perception
limitations.
New work by Richard Robinson shows promise in establishing the
brain functions involved in this model and may help shed light on how we
understand signs or symbols and reference these to our semiotic
registers.
Daniel Kolak
has argued extensively against the existence of a stream of
consciousness, in the sense of someone having a continuous identity over
time, in his book I am You.
Kolak describes three opposing philosophical views regarding the
continuity of consciousness: Closed individualism, Empty individualism,
and Open individualism.
Closed Individualism is defined as the default common sense view of
identity where one's identity consists of a line stretching across time,
which Kolak, argues is incoherent. Empty Individualism is the view that
one's identity only exists for an infinitesimally small amount of time,
and an individual person has an entirely different identity from moment
to moment. Kolak instead advocates for Open Individualism, which is the
view that everyone is in reality the same being, and that the "self"
doesn't actually exist at all, similar to anattā in Buddhist philosophy.
Derek Parfit
is another philosopher who has challenged the idea of the existence of a
continuous stream of consciousness over time. In his book Reasons and Persons, Parfit describes the teletransportation paradox thought experiment, which describes the difficulties in distinguishing one's future self from an entity that is merely a copy of oneself.
In literature, stream of consciousness writing is a literary device
which seeks to portray an individual's point of view by giving the
written equivalent of the character's thought processes, either in a
loose interior monologue, or in connection to his or her sensory
reactions to external occurrences. Stream-of-consciousness as a narrative device is strongly associated with the modernist movement. The term was first applied in a literary context, transferred from psychology, in The Egoist, April 1918, by May Sinclair, in relation to the early volumes of Dorothy Richardson's novel sequence Pilgrimage. Amongst other modernist novelists who used it are James Joyce in Ulysses (1922) and William Faulkner in The Sound and the Fury (1929).
In science fiction, inner space refers to works of psychological science fiction
that emphasize internal, mental, and emotional experiences over
external adventure or technological speculation, which defined it as "a
category introduced to science fiction by representatives of the New
Wave to designate internal, mental experiences as imaginary worlds with
no connection to the real world" contrasts with traditional science
fiction's fascination with outer space.
Works from this genre appeared as part of the emergence of the New Wave in science fiction in the 1960s. They were popularized by English writer J.G. Ballard and associated with the New Wave movement in science fiction. Subsequent contributions by critics and writers such as Michael Moorcock, Pat Cadigan, and Greg Bear helped establish inner space as a recurring theme in science fiction discourse.
Rob Mayo wrote that the 1980s was the second "golden age" of inner space, associated with writers such as Pat Cadigan and Greg Bear; he also notes the movie Dreamscape
(1984), which he calls "the first inner space film". He notes that the
genre once again returned the 2000s, here noting the movies The Cell (2000) and Inception (2010), as well as the video game Psychonauts (2005). He notes that Inception marked "the transition of inner space fiction from a marginal genre (SF literature) to a viable mainstream (Hollywood cinema)".
Idealism in philosophy, also known as philosophical idealism or metaphysical idealism, is the set of metaphysical perspectives asserting that, most fundamentally, reality is equivalent to mind, spirit, or consciousness;
that reality or truth is entirely a mental construct; or that ideas are
the highest type of reality or have the greatest claim to being
considered "real". Because there are different types of idealism, it is difficult to define the term uniformly.
Indian philosophy contains some of the first defenses of idealism, such as in Vedanta and in ShaivaPratyabhijña
thought. These systems of thought argue for an all-pervading
consciousness as the true nature and ground of reality. Idealism is also
found in some streams of Mahayana Buddhism, such as in the Yogācāra school, which argued for a "mind-only" (cittamatra) philosophy on an analysis of subjective experience. In the West, idealism traces its roots back to Plato in ancient Greece, who proposed that absolute, unchanging, timeless ideas constitute the highest form of reality: Platonic idealism. This was revived and transformed in the early modern period by Immanuel Kant's arguments that our knowledge of reality is completely based on mental structures: transcendental idealism.
Epistemologically, idealism is accompanied by a rejection of the possibility of knowing the existence of any thing independent of mind. Ontologically,
idealism asserts that the existence of all things depends upon the
mind; thus, ontological idealism rejects the perspectives of physicalism and dualism. In contrast to materialism, idealism asserts the primacy of consciousness as the origin and prerequisite of all phenomena.
Idealism came under attack from proponents of analytical philosophy, such as G. E. Moore and Bertrand Russell, but its critics also included the new realists and Marxists. However, many aspects and paradigms of idealism still have a large influence on subsequent philosophy.
Definitions
Idealism is a term with several related meanings. It comes via Latinidea from the Ancient Greekidea (ἰδέα) from idein (ἰδεῖν), meaning "to see". The term entered the English language by 1743. The term idealism was first used in the abstract metaphysical sense of the "belief that reality is made up only of ideas" by Christian Wolff in 1747. The term re-entered the English language in this abstract sense by 1796. A. C. Ewing gives this influential definition:
the view that there can be no physical objects existing
apart from some experience...provided that we regard thinking as part of
experience and do not imply by "experience" passivity, and provided we
include under experience not only human experience but the so-called
"Absolute Experience" or the experience of a God such as Berkeley postulates.
A more recent definition by Willem deVries
sees idealism as "roughly, the genus comprises theories that attribute
ontological priority to the mental, especially the conceptual or
ideational, over the non-mental." As such, idealism entails a rejection of materialism (or physicalism) as well as the rejection of the mind-independent existence of matter (and as such, also entails a rejection of dualism).
There are two main metaphysical concepts on the position of
idealism in contemporary philosophy, depending on whether its thesis is
ontological or epistemic:
Ontological
idealism is the view which holds that all of reality is in some way
mental (or spirit, reason, or will) or at least ultimately grounded in a
fundamental basis which is mental. This is a form of metaphysical monism
because it holds that there is only one type of thing in existence. The
modern paradigm of a Western metaphysical idealism is Berkeley's
immaterialism. Other such idealists are Hegel, and Bradley.
Epistemological idealism (or "formal" idealism) is a position in epistemology that holds that all knowledge
is based on mental structures, not on "things in themselves". Whether a
mind-independent reality is accepted or not, all that we have knowledge
of are mental phenomena. The main source of Western epistemic idealist arguments is the transcendental idealism of Kant. Other thinkers who have defended epistemic idealist arguments include Ludwig Boltzmann and Brand Blanshard.
Thus, ontological idealism holds that reality itself is non-physical, immaterial, or experiential at its core, while epistemological idealist
arguments merely affirm that reality can only be known through ideas
and mental structures (without necessarily making metaphysical claims
about things in themselves). Because of this, A.C. Ewing argued that instead of thinking about these
two categories as forms of idealism proper, we should instead speak of
epistemic and ontological arguments for idealism.
These two ways of arguing for idealism are sometimes combined to
defend a specific type of idealism (as done by Berkeley), but they may
also be defended as independent theses by different thinkers. For
example, while F. H. Bradley and McTaggart focused on metaphysical
arguments, Josiah Royce, and Brand Blanshard developed epistemological arguments.
Furthermore, one might use epistemic arguments, but remain
neutral about the metaphysical nature of things in themselves. This
metaphysically neutral position, which is not a form of metaphysical
idealism proper, may be associated with figures like Rudolf Carnap, Quine, Donald Davidson, and perhaps even Kant himself (though he is difficult to categorize). The most famous kind of epistemic idealism is associated with Kantianism and transcendental idealism, as well as with the related Neo-Kantian
philosophies. Transcendental idealists like Kant affirm epistemic
idealistic arguments without committing themselves to whether reality as
such, the "thing in itself", is ultimately mental.
Types of ontological idealism
Within ontological idealism, there are numerous further sub-types, including forms of pluralism, which hold that there are many independent mental substances or minds, such as Leibniz' monadology, and various forms of monism or absolute idealism (e.g. Hegelianism or Advaita Vedanta), which hold that the fundamental mental reality is a single unity or is grounded in some kind of singular Absolute. Beyond this, idealists disagree on which aspects of the mental are more metaphysically basic. Platonic idealism affirms that ideal forms are more basic to reality than the things we perceive, while subjective idealists and phenomenalists privilege sensory experiences. Personalism, meanwhile, sees persons or selves as fundamental.
A common distinction is between subjective and objective forms of idealism. Subjective idealists like George Berkeley reject the existence of a mind-independent or "external" world (though not the appearance of such phenomena in the mind). However, not all idealists restrict the real to subjective experience. Objective idealists
make claims about a trans-empirical world, but simply deny that this
world is essentially divorced from or ontologically prior to mind or
consciousness as such. Thus, objective idealism asserts that the reality
of experiencing includes and transcends the realities of the object
experienced and of the mind of the observer.
Idealism is sometimes categorized as a type of metaphysical anti-realism or skepticism.
However, idealists need not reject the existence of an objective
reality that we can obtain knowledge of, and can merely affirm that this
real natural world is mental.Thus, David Chalmers writes of anti-realist idealisms (which would include Berkeley's) and realist forms of idealism, such as "panpsychist
versions of idealism where fundamental microphysical entities are
conscious subjects, and on which matter is realized by these conscious
subjects and their relations."
Chalmers further outlines the following taxonomy of idealism:
Micro-idealism
is the thesis that concrete reality is wholly grounded in micro-level
mentality: that is, in mentality associated with fundamental microscopic
entities (such as quarks and photons).
Macro-idealism is the thesis that concrete reality is wholly grounded
in macro-level mentality: that is, in mentality associated with
macroscopic (middle-sized) entities such as humans
and perhaps non-human animals. Cosmic idealism is the thesis that
concrete reality is wholly grounded in cosmic mentality: that is, in
mentality associated with the cosmos as a whole or with a single cosmic entity (such as the universe or a deity).
Guyer et al. also distinguish between forms of idealism which are grounded in substance theory
(often found in the Anglophone idealisms of the late nineteenth and
twentieth centuries) and forms of idealism which focus on activities or
dynamic processes (favored in post-Kantian German philosophy).
Classical Greek idealism
Pre-Socratic philosophy
There are some precursors of idealism in Ancient Greek Philosophy, though scholars disagree on whether any of these thinkers could be properly labeled "idealist" in the modern sense. One example is Anaxagoras (480 BC) who taught that all things in the universe (apeiron) were set in motion by nous ("mind"). In the Phaedo, Plato quotes him as saying, "it is intelligence [nous] that arranges and causes all things". Similarly, Parmenides famously stated that "thinking and being are the same". This has led some scholars, such as Hegel and E. D. Phillips, to label Parmenides an idealist.
Plato's theory of forms or "ideas" (eidos) as described in dialogues like Phaedo, Parmenides and Sophist, describes ideal forms (for example the platonic solids in geometry or abstracts like Goodness and Justice), as perfect beings which "exists-by-itself" (Greek: auto kath' auto), that is, independently of any particular instance (whether physical or in the individual thought of any person). Anything that exists in the world exists by participating in one of
these unique ideas, which are nevertheless interrelated causally with
the world of becoming, with nature. Arne Grøn calls this doctrine "the classic example of a metaphysical idealism as a transcendent idealism". Nevertheless, Plato holds that matter as perceived by us is real,
though transitory, imperfect, and dependent on the eternal ideas for its
existence. Because of this, some scholars have seen Plato as a dualist, though others disagree and favor a monist account.
The thought of Plato was widely influential, and later Late Platonist (or Neoplatonist) thinkers developed Platonism in new directions. Plotinus, the most influential of the later Platonists, wrote "Being and Intellect are therefore one nature" (Enneads V.9.8). According to scholars like Nathaniel Alfred Boll and Ludwig Noiré, with
Plotinus, a true idealism which holds that only soul or mind exists
appears for the first time in Western philosophy. Similarly, for Maria Luisa Gatti, Plotinus' philosophy is a
"'contemplationist metaphysics', in which contemplation, as creative,
constitutes the reason for the being of everything". For Neoplatonist thinkers, the first cause or principle is the Idea of the Good, i.e. The One, from which everything is derived a hierarchical procession (proodos) (Enn. VI.7.15).
Idealism in Judaism and Christianity
Some Christian theologians have held idealist views, often based on neoplatonism. Christian neoplatonism included figures like Pseudo-Dionysius the Areopagite, and influenced numerous Christian thinkers, including the Cappadocian Fathers and Augustine. Despite the influence of Aristotelianscholasticism from the 12th century onward, there is certainly a sense in which some medieval scholastic philosophers retained influences from the Platonic idealism that came via Augustine. For example, the work of John Scotus Eriugena (c. 800 – c. 877) has been interpreted as an idealistic philosophy by Dermot Moran
who writes that for Scotus "all spatiotemporal reality is understood as
immaterial, mind dependent, and lacking in independent existence". Scotus thus wrote: "the intellection of all things...is the being of all things".
Idealism was also defended in medieval Jewish philosophy. According to Samuel Lebens, early Hassidic rabbis like Yitzchak Luria (1534–72) defended a form of Kabbalistic idealism in which the world was God's dream or a fictional tale told by God.
Later Western theistic idealism such as that of Hermann Lotze
offers a theory of the "world ground" in which all things find their
unity: it has been widely accepted by Protestant theologians.
Several modern religious movements such as, for example, the organizations within the New Thought Movement and the Unity Church, may be said to have a particularly idealist orientation. The theology of Christian Science
includes a form of idealism: it teaches that all that truly exists is
God and God's ideas; that the world as it appears to the senses is a
distortion of the underlying spiritual reality, a distortion that may be
corrected (both conceptually and in terms of human experience) through a
reorientation (spiritualization) of thought.
Idealism in Eastern philosophy
There are currents of idealism throughout Indian philosophy, ancient and modern. Some forms of Hindu idealism (like Advaita) defend a type of monism or non-dualism, in which a single consciousness (brahman) is all that exists. However, other traditions defend a theistic pluralism (e.g. Shaiva Siddhanta), in which there are many selves (atman) and one God.
Buddhist idealism on the other hand is non-theistic and does not accept the existence of eternal selves (due to their adherence to the theory of not-self).
Hindu philosophy
The Upanishadic sageYājñavalkya (c. possibly 8th century BCE) is one of the earliest exponents of idealism, and is a major figure in the Bṛhadāraṇyaka Upaniṣad.
A type of idealistic monism can be seen in the Upanishads, which often describe the ultimate reality of brahman as "being, consciousness, bliss" (Saccidānanda). The Chāndogya Upaniṣad
teaches that everything is an emanation of the immortal brahman, which
is the essence and source of all things, and is identical with the self (atman). The Bṛhadāraṇyaka Upaniṣad
also describes brahman as awaress and bliss, and states that "this
great being (mahad bhūtam) without an end, boundless (apāra), [is]
nothing but vijñāna [consciousness]."
Different schools of Vedanta have different interpretations of
brahman-atman, their foundational theory. Advaita Vedanta posits an
absolute idealistic monism in which reality is one single absolute
existence. Thus, brahman (the ultimate ground of all) is absolutely
identical with all atmans (individual selves). Other forms of Vedanta
like the Vishishtadvaita of Ramanuja and the Bhedabheda of Bhāskara are not as radical in their non-dualism, accepting that there is a certain difference between individual souls and Brahman.
The most influential Advaita philosopher was Ādi Śaṅkara (788–820). In his philosophy, brahman is the single non-dual foundation (adhiṣṭhana)
for all existence. This reality is independent, self-established,
irreducible, immutable, and free of space, time, and causation. In comparison to this reality, the world of plurality and appearances is illusory (maya),
an unreal cognitive error (mithya). This includes all individual souls
or selves, which are actually unreal and numerically identical to the
one brahman.
Śaṅkara did not believe it was possible to prove the view that reality is "one only, without a second" (Chandogya
6.2.1) through independent philosophical reasoning. Instead, he accepts
non-duality based on the authority of the Upaniṣads. As such, most of
his extant works are scriptural commentaries.
Nevertheless, he did provide various new arguments to defend his
theories. A major metaphysical distinction for Śaṅkara is between what
changes and may thus be negated (the unreal) and what does not (which is
what is truly real). He compares the real to clay (the substantial cause, analogous to
brahman) and the unreal to a pot which depends on the clay for its being
(analogous to all impermanent things in the universe). By relying on dependence relations and on the reality of persistence,
Śaṅkara concludes that metaphysical foundations are more real than their
impermanent effects, and that effects are fully reducible and indeed
identical to their metaphysical foundation. Through this argument from dependence, Śaṅkara concludes that since all
things in the universe undergoes change, they must depend on some
really existent cause for their being, and this is the one primordial
undifferentiated existence (Chandogya Bhāṣya, 6.2.1–2). This one reality is the single cause that is in every object, and every
thing is not different from this brahman since all things borrow their
existence from it. Śaṅkara also provides a cosmogony in which the world arises from an unmanifest state which is like deep dreamless sleep into a state in which īśvara (God) dreams the world into existence. As such, the world is not separate from God's mind.
Śaṅkara's philosophy, along with that of his contemporary Maṇḍana Miśra
(c. 8th century CE), is at the foundation of Advaita school. The
opponents of this school however, labeled him a māyāvādin (illusionist)
for negating the reality of the world. They also criticized what they saw as a problematic explanation for how
the world arises from māyā as an error. For them, if māyā is in
brahman, then brahman has ignorance, but if it is not in brahman, then
this collapses into a dualism of brahman and māyā.
Other idealist schools
Perhaps the most influential critic of Advaita was Rāmānuja (c. 1017 – c. 1137), the main philosopher of the competing Viśiṣṭādvaita
(qualified non-dual) school. His philosophy affirms the reality of the
world and individual selves as well as affirming an underlying unity of
all things with God. One of Rāmānuja's critiques of advaita is epistemological. If, as
Advaita argues, all cognition other than pure undifferentiated
consciousness is based in error, then it follows we would have no
knowledge of the very fact that all individual cognition is error (Śrī Bhāṣya, I.i.1).
Furthermore, Rāmānuja also argues contra Advaita that individual
selves are real and not illusory. This is because the very idea that an
individual can be ignorant presupposes the very existence of that
individual. Furthermore, since all Vedāntins agree that Brahman's nature is
knowledge, consciousness and being, to say that brahman is ignorant is
absurd, and so it must be individual souls which are ignorant. Thus, there must be individual selves with a metaphysically prior existence who then fall into ignorance (Śrī Bhāṣya, I.i.1.). Selves might be individual, but as the Vedas
state, they still share a sense of unity with brahman. For Rāmānuja,
this is because selves are distinct modes or qualities in the cosmic body of Brahman (and are thus different and yet united with brahman).Brahman meanwhile is like the soul in the body of the world.
Furthermore, brahman is a theistic creator God for Rāmānuja, which
really exists as the union of two deities: Vishnu, and Lakṣmī.
The philosophy of the Tantric tradition of Trika Shaivism is a non-dual theistic idealism. The key thinkers of this philosophical tradition, known as the Pratyabhijñā (Recognition) school, are the Kashmirian philosophers Utpaladeva (c. 900–950 CE) and Abhinavagupta (975–1025 CE). This tradition affirms a non-dual monism which sees God (Shiva) as a single cosmic consciousness. All selves (atman) are one with God, but they have forgotten this, and
must recognize their true nature in order to reach liberation.
Unlike in Advaita Vedanta however, the one cosmic consciousness is active and dynamic, consisting of spontaneous vibration (spanda) since it has the quality of absolute freedom (svātāntrya). Through the power (Śakti)
of dynamic vibrations, the absolute (Shiva-Śakti, consciousness and its
power) creates the world, and so, the world is a real manifestation of
absolute consciousness. Thus, in this system, the world and individual selves (which are
dynamic, not an unchanging witness) are not an unreal illusion, but are
seen as real and active expressions of God's creative freedom.
There is some modern scholarly disagreement about whether Indian Yogācāra Buddhism can be said to be a form of idealism. Some writers like philosopher Jay Garfield and German philologist Lambert Schmithausen argue that Indian Yogacarins are metaphysical idealists that reject the existence of a mind independent external world. Others see them as closer to an epistemic idealist like Kant who holds
that our knowledge of the world is simply knowledge of our own concepts
and perceptions. However, a major difference here is that while Kant holds that the
thing-in-itself is unknowable, Indian Yogacarins held that ultimate
reality is knowable, but only through the non-conceptual yogic
perception of a highly trained meditative mind. Other scholars like Dan Lusthaus and Thomas Kochumuttom see Yogācāra as a kind of phenomenology of experience which seeks to understand how suffering (dukkha) arises in the mind, not provide a metaphysics.
Vasubandhu
Statue of Vasubandhu (jp. Seshin), Kōfuku-ji, Nara, Japan
Whatever the case, the works of Vasubandhu
(fl. c.360) certainly include a refutation of mind-independent
"external" objects (Sanskrit: bāhyārtha) and argue that the true nature
of reality is beyond subject-object distinctions. He views ordinary conscious experience as deluded in its perceptions of
an external world separate from itself (which does not exist), and
instead argues that all there is vijñapti (ideas, mental images, conscious appearances, representations). Vasubandhu begins his Twenty verses (Viṃśikā) by affirming that "all this [everything we take to exist] is mere appearance of consciousness [vijñapti], because of the appearance of non-existent objects, just as a man with an eye disease sees non-existent hairs" (Viṃś.1). His main argument against external objects is a critique of the atomist theories of his realist opponents (Nyāya and Abhidharma theorists).
Vasubandhu also responds against three objections to idealism
which indicate his view that all appearances are caused by mind: (1) the
issue of spatio-temporal continuity, (2) accounting for intersubjectivity, and (3) the causal efficacy of matter on subjects. For the first and third objections, Vasubandhu responds by arguing that
dreams can also include spatio-temporal continuity, regularity and
causal efficacy. Regarding intersubjectivity, Vasubandhu appeals to shared karma as well as mind to mind causation. After answering these objections, Vasubandhu argues that idealism is a better explanation than realism for everyday experiences. To do this, he relies on the Indian "Principle of Lightness" (an appeal to parsimony like Occam's Razor) and argues that idealism is the "lighter" theory since it posits a smaller number of entities. This is thus an argument from simplicity and an inference to the best explanation (i.e. an abductive argument).
As such, he affirms that our usual experience of being a self
(ātman) that knows objects is an illusory construct, and this
constitutes what he calls the "imagined nature" aspect of reality.
Thus, for Vasubandhu, there is a more fundamental "root
consciousness" that is empty of subject-object distinctions and yet
originates all experiences "just as waves originate on water" (Thirty Verses, Triṃś.17). However, Vasubandhu sees this philosophy as a mere conventional description, since ultimate reality is "inconceivable" (Triṃś.29), an ineffable and non-conceptual "thusness" which cannot be fully captured in words and can only be known through meditative realization by yogis
("yogacaras", hence the name of his school). This is why certain modern
interpreters, like Jonathan Gold, see Vasubandhu's thought as a
"conventionalist idealism" or even a type of epistemic idealism like
Kant's (and not a full blown objective idealism).
The Buddhist epistemologists
Buddhist arguments against external objects were further expanded and sharpened by later figures like Dignāga (fl. 6th century) and Dharmakīrti (fl. 7th century) who led an epistemological turn in medieval Indian philosophy.
Dignāga's main arguments against external objects (specifically, atomicparticles) are found in his Ālambanaparīkṣā (Examination of the Object of Consciousness). Dignāga argues that for something to be an object (ālambana) of a
conscious state, that object must be causally related to the
consciousness and it must resemble that consciousness (in appearance or
content). Dignāga then attempts to show that realism about external
particulars cannot satisfy these two conditions. Since individual atoms lack a resemblance to the conscious state they
supposedly cause, they cannot be the object of cognition. Furthermore,
aggregates of atoms also cannot be the object, since they are merely a
conceptual grouping of individual atoms (and thus, unreal), and only
atoms have causal efficacy.
Dharmakīrti's view is summed up in the Pramānaṿārttika (Commentary on Epistemology)
as follows: "cognition experiences itself, and nothing else whatsoever.
Even the particular objects of perception, are by nature just
consciousness itself." One of his main arguments for idealism is the inference from "the
necessity of things only ever being experienced together with
experience" (Sanskrit: sahopalambhaniyama). Dharmakīrti consicely states this argument in the Ascertainment of Epistemology (Pramāṇaviniścaya): "blue and the consciousness of blue are not different, because they must always be apprehended together." Since an object is never found independently of consciousness, objects
cannot be mind-independent. This can be read as an epistemological
argument for idealism which attempts to show there is no good reason
(empirically or inferentially) to accept the existence of external
objects.
Most of the Yogācāra thinkers and epistemologists (including Dharmakīrti) defended the existence of multiple mindstreams, and even tackled the problem of other minds.
As such, thinkers like Dharmakīrti were pluralists who held there were
multiple minds in the world (in this they differ with Hindu Advaita
thinkers who held there was a single cosmic consciousness). However, there was a certain sub-school of Indian Buddhists, exemplified by Prajñakaragupta, Jñānaśrīmitra (fl. 975–1025 C.E.) and Ratnakīrti (11th century CE) who were not pluralists. In his Refutation of Other mindstreams (Santānāntaradūṣaṇa),
Ratnakīrti argues that the existence of other minds cannot be
established ultimately, and as such ultimate reality must be an
undifferentiated non-dual consciousness (vijñānādvaita). This monistic interpretation of Yogācāra is known as the Citrādvaitavāda school (the view of variegated non-duality) since it sees reality as a single multifaceted non-dual luminosity (citrādvaitaprakāśa).
Yogācāra Buddhism also influenced the thought of other Chinese Buddhist philosophical traditions, such as Huayan, Tiantai, Pure Land, and Zen. Many Chinese Buddhist traditions like Huayan, Zen, and Tiantai were also strongly influenced by an important text called the Awakening of Faith in the Mahāyāna, which synthesized consciousness-only idealism with buddha-nature thought. This text promoted an influential theory of mind which holds that all
phenomena are manifestations of the "One Mind". Some scholars have seen
this as an ontological monism. One passage from the text states: "the three worlds
are illusory constructs, created by the mind alone" and "all dharmas
are produced from the mind's giving rise to false thoughts". Jorgensen et al. note that this indicates metaphysical idealism. The new philosophical trend ushered in by the Awakening of Faith
was resisted by some Chinese Yogācāra thinkers, and the debates between
the Yogācāra school of Xuanzang and those who instead followed the
doctrines of the Awakening of Faith continued until the modern era. These debates happened in China as well as in Japan and Korea.
The doctrine that all phenomena arise from an ultimate principle, the One Mind, was adapted by the influential Huayan school, whose thought is exemplified by thinkers such as Fazang (643–712) and Zongmi (780–841). This tradition also promoted a kind of holism which sees every phenomenon in the cosmos as interfused and interconnected with every other phenomenon. Chinese scholars like Yu-lan Fung and Wing-tsit Chan see Huayan philosophy as a form of idealism, though other scholars have defended alternative interpretations.According to Wing-tsit Chan, since Huayan patriarch Fazang sees the One
Mind as the basis for all things, including the external world, his
system is one of objective idealism. A key distinction between Huayan's view of the world and that of the
Yogācāra school is that in Huayan, there is a single intersubjective
world (which nevertheless arises from mind), while Yogācāra holds that
each mindstream projects its own world out of their underlying root
consciousness.
Chinese Buddhist idealism also influenced Confucian philosophy through the work of thinkers like the Ming era (1368–1644) neo-confucianWang Yangming (1472–1529). Wang's thought has been interpreted as a kind of idealism. According to Wang, the ultimate principle or pattern (lǐ) of the whole universe is identical with the mind, which forms one body or substance (yì tǐ) with "Heaven, Earth, and the myriad creatures" of the world. Wang argues that only this view can explain the fact that human beings experience innate care and benevolence for others as well as a sense of care for inanimate objects. Wang's thought, along with that of Lu Xiangshan, led to the creation of the School of Mind, an important Neo-Confucian tradition which emphasized these idealist views.
Yogācāra idealism saw a revival in the 20th century, associated figures like Yang Wenhui (1837–1911), Taixu, Liang Shuming, Ouyang Jingwu (1870–1943), Wang Xiaoxu (1875–1948), and Lu Cheng. Modern Chinese thinkers associated with consciousness-only linked the
philosophy with Western philosophy (especially Hegelian and Kantian
thought) and modern science.A similar trend occurred among some Japanese philosophers like Inoue Enryō, who linked East Asian philosophies like Huayan with the philosophy of Hegel.
Both modern Chinese Buddhists and New Confucian thinkers participated in this revival of consciousness-only studies. The thought of New Confucians like Xiong Shili, Ma Yifu, Tang Junyi and Mou Zongsan, was influenced by Yogācāra consciousness-only philosophy, as well as by the metaphysics of the Awakening of Faith in the Mahāyāna, though their thought also contained many critiques of Buddhist philosophy.
Modern philosophy
It is only in the modern era that idealism became a central topic of argumentation among Western philosophers. This was also when the term "idealism" coined by Christian Wolff (1679–1754), though previous thinkers like Berkeley had argued for it under different names.
Idealistic tendencies can be found in the work of some rationalist philosophers, like Leibniz and Nicolas Malebranche
(though they did not use the term). Malebranche argued that Platonic
ideas (which exist only in the mind of God) are the ultimate ground of
our experiences and of the physical world, a view that prefigures later
idealist positions. Some scholars also see Leibniz' philosophy as approaching idealism. Guyer et al. write that "his view that the states of monads
can be only perceptions and appetitions (desires) suggests a
metaphysical argument for idealism, while his famous thesis that each
monad represents the entire universe from its own point of view might be
taken to be an epistemological ground for idealism, even if he does not
say as much." However, there is still much debate in the contemporary scholarly literature on whether Leibniz can be considered an idealist.
A painting of Bishop George Berkeley by John Smibert
One famous proponent of modern idealism was Bishop George Berkeley (1685–1753), an Anglo-Irish philosopher who defended a theory he called immaterialism. This kind of idealism is sometimes also called subjective idealism (also known as phenomenalistic idealism).
Berkeley held that objects exist only to the extent that a mind
perceives them and thus the physical world does not exist outside of
mind. Berkeley's epistemic argument for this view (found in his A Treatise Concerning the Principles of Human Knowledge) rests on the premise that we can only know ideas in the mind. Thus, knowledge does not extend to mind-independent things (Treatise, 1710: Part I, §2). From this, Berkeley holds that "the existence of an idea consists in being perceived", thus, regarding ideas "their esse is percipi", that is, to be is to be perceived (1710: Part I, §3).
Based on this restriction of existence to only what is being
perceived, Berkeley holds that it is meaningless to think that there
could exist objects that are not being perceived. This is the basic idea behind what has been called Berkeley's "master argument"
for idealism, which states that "one cannot conceive of anything
existing unconceived because in trying to do so one is still conceiving
of the object" (1710: Part I, §23). As to the question of how objects which are currently not being
perceived by individual minds persist in the world, Berkeley answers
that a single eternal mind keeps all of physical reality stable (and
causes ideas in the first place), and this is God.
Berkeley also argued for idealism based on a second key premise:
"an idea can be like nothing but an idea" and as such there cannot be
any things without or outside mind. This is because for something to be
like something else, there must be something they have in common. If
something is mind independent, then it must be completely different from
ideas. Thus, there can be no relation between ideas in the mind and
things "without the mind", since they are not alike. As Berkeley writes, "...I ask whether those supposed originals or
external things, of which our ideas are the pictures or representations,
be themselves perceivable or no? if they are, then they are ideas, and
we have gained our point; but if you say they are not, I appeal to any
one whether it be sense, to assert a colour is like something which is
invisible; hard or soft, like something which is intangible; and so of
the rest." (1710: Part I, §8).
A similar idealistic philosophy was developed at around the same time as Berkeley by Anglican priest and philosopher Arthur Collier (Clavis Universalis: Or, A New Inquiry after Truth, Being a Demonstration of the Non-Existence, or Impossibility, of an External World, 1713). Collier claimed to have developed his view that all matter depends on mind independently of Berkeley. Paul Brunton, a British philosopher and mystic, also taught a similar type of idealism called "mentalism".
A. A. Luce and John Foster are other subjective idealists. Luce, in Sense without Matter
(1954), attempts to bring Berkeley up to date by modernizing his
vocabulary and putting the issues he faced in modern terms, and treats
the Biblical account of matter and the psychology of perception and
nature. Foster's The Case for Idealism argues that the physical world is the logical creation of natural, non-logical constraints on human sense-experience. Foster's latest defense of his views (phenomenalistic idealism) is in his book A World for Us: The Case for Phenomenalistic Idealism.
Transcendental idealism was developed by Immanuel Kant (1724–1804), who was the first philosopher to label himself an "idealist". In his Critique of Pure Reason,
Kant was clear to distinguish his view (which he also called "critical"
and "empirical realism") from Berkeley's idealism and from Descartes's
views. Kant's philosophy holds that we only have knowledge of our experiences,
which consists jointly of intuitions and concepts. As such, our
experiences reflect our cognitive structures, not the intrinsic nature
of mind-independent things. This means even time and space are not
properties of things in themselves (i.e. mind independent reality underlying appearances).
Since it focuses on the mind dependent nature of knowledge and not on metaphysics per se, transcendental idealism is a type of epistemological idealism.
Unlike metaphysical forms of idealism, Kant's transcendental idealism
does not deny the existence of mind independent things or affirm that
they must be mental. He thus accepts that we can conceive of external objects as distinct
from our representations of them. However, he argues that we cannot know
what external objects are "in themselves". As such, Kant's system can be called idealist in some respects (e.g.
regarding space and time) and also realist in that he accepts there must
be some mind independent reality (even if we cannot know its ultimate nature and thus must remain agnostic about this). Kant's system also affirms the reality of a free truly existent self
and of a God, which he sees as being possible because the non-temporal
nature of the thing-in-itself allows for a radical freedom and genuine
spontaneity.
Kant's main argument for his idealism, found throughout the Critique of Pure Reason, is based on the key premise that we always represent objects in space and time through our a priori intuitions (knowledge which is independent from any experience). Thus, according to Kant, space and time can never represent any
"property at all of any things in themselves nor any relations of them
to each other, i.e., no determination of them that attaches to objects
themselves and that would remain even if one were to abstract from all
subjective conditions of intuition" (CPuR A 26/B 42).
Kant's main point is that since our mental representations have
spatio-temporal structure, we have no real grounds for positing that the
real objects our mind represents in this way also have spatio-temporal
structure in themselves. Kant makes this argument in different parts of
the Critique, such as when he asks rhetorically:
If
there did not lie in you a faculty for intuiting a priori; if this
subjective condition were not at the same time the universal a priori
condition under which alone the object of ... intuition is possible; if
the object ([e.g.,] the triangle) were something in itself without
relation to your subject: then how could you say that what necessarily
lies in your subjective conditions for constructing a triangle must also
necessarily pertain to the triangle in itself. (A 48/B 65)
Throughout
his career, Kant labored to distinguish his philosophy from
metaphysical idealism, as some of his critics charged him with being a
Berkeleyian idealist. He argued that even if we cannot know how things are in themselves, we
do know they must exist, and that we know this "through the
representations which their influence on our sensibility provides for
us." In the second edition of his Critique,
he even inserted a "refutation of idealism". For Kant, "the perception
of this persistent thing is possible only through a thing outside me and
not through the mere representation of a thing outside me."
The mid-19th century saw a revival of Kantian philosophy, which became known as Neo-Kantianism, with its call of "Back to Kant". This movement was especially influential on 19th century German
academic philosophy (and also continental philosophy as a whole). Some
important figures include: Hermann Cohen (1842–1918), Wilhelm Windelband (1848–1914), Ernst Cassirer, Hermann von Helmholtz, Eduard Zeller, Leonard Nelson, Heinrich Rickert, and Friedrich Albert Lange.A key concern of the Neo-Kantians was to update Kantian epistemology,
particularly in order to provide an epistemic basis for the modern
sciences (all while avoiding ontology altogether, whether idealist or
materialist). Neo-Kantianism rejected metaphysical idealism while also accepting the
basic Kantian premise that "our experience of reality is always
structured by the distinctive features of human mentality." Hence, Cassirer defended an epistemic worldview that held that one
cannot reduce reality to any independent or substantial object (physical
or mental), instead, there are only different ways of describing and
organizing experience.
Neo-Kantianism influenced the work of the Vienna circle and its ambassadors to the Anglophone world, Rudolf Carnap 1891–1970) and Hans Reichenbach. Charles Bernard Renouvier was the first philosopher in France to formulate a system based on Kant's critical idealism, which he termed Neo-criticism (néo-criticisme). It is a transformation rather than a continuation of Kantianism.
Several important German thinkers who were deeply influenced by Kant are the German idealists: Johann Gottlieb Fichte (1762–1814), Friedrich Wilhelm Joseph Schelling (1775–1854), and Georg Friedrich Hegel (1770–1831). Though heavily drawing on Kant, these thinkers were not transcendental
idealists as such, and they sought to move beyond the idea that things
in themselves are unknowable –an idea they considered as opening the
door to skepticism and nihilism.
Post-Kantian German idealists thus rejected transcendental
idealism by arguing against the opposition of a mind-independent world
of being and a subjective world of mental constructs (or the separation
between the knowledge and what is known, between subject and object,
real and ideal). This new German idealism was distinguished by an
"inseparability of being and thinking" and "a dynamic conception of
self-consciousness" that sees reality as spontaneous conscious activity
and its expressions. As such, this kind of metaphysical idealism, focused on dynamic
processes and forces, was opposed to older forms of idealism, which
based itself on substance theory (which these Germans labeled
"dogmatism").
The first thinker to elaborate this type of dynamic idealism was J. G. Fichte (Doctrine of Wissenschaft, 1810–1813). For Fichte, the primordial act at the ground of being is called "self-positing". Fichte argues that self-consciousness or the I is a spontaneous
unconditioned self-creating act which he also called the deed-act (tathandlung).
Fichte argues that positing something unconditioned and independent at
the ground of all is the only way to avoid an epistemic infinite regress. According to Fichte, this "I am" or "absolute subject" which "originally posits its own being absolutely" (Doctrine
I, 2: 261), "is at the same time the actor and the product of the act;
the actor, and that which the activity brings forth; act and deed are
one and the same" (Doctrine I, 2: 259). Fichte also argues that this "I" has the capacity to "counter-posit" a "not-I", leading to a subject-object
relationship. The I also has a third capacity Fichte calls
"divisibility", which allows for the existence of plurality in the
world, which however must be understood as manifestations of the
"I-activity", and as being "within the I".
Fichte's philosophy was adopted by Schelling who defended this new idealism as a full monistic ontology which tried to account for all of nature which he would eventually name "absolute idealism". For Schelling, reality is an "original unity" (ursprüngliche Einheit) or a "primordial totality" (uranfängliche Ganzheit) of opposites. This is an absolute which he described as an "eternal act of cognition"
is disclosed in subjective and objective modes, the world of ideas and
nature.
G. W. F. Hegel
also defended a dynamic absolute idealism that sees existence as an
all-inclusive whole. However, his system differs from his predecessors'
in that it is not grounded on some initial subject, mind, or "I" and
tries to move beyond all bifurcation subject and object, of the dualism
between thinking and being (which for Hegel just leads to various
contradictions).As such, Hegel's system is an ontological monism fundamentally based on
a unity between being and thought, subject and object, which he saw as
being neither materialistic realism nor subjective idealism (which still
stands in an opposition to materialism and thus remains stuck in the
subject-object distinction).
In his Phenomenology of Spirit
(1807), Hegel provides an epistemological argument for idealism,
focusing on proving the "metaphysical priority of identities over and
against their opposed elements". Hegel's argument begins with his conception of knowledge, which he
holds is a relation between a claim about a subject and an object that
allows for a correspondence between their structural features (and is
thus a type of correspondence theory).
Hegel argues that if knowledge is possible, real objects must also have
a similar structure as thought (without, however, being reduced to
thoughts). If not, there could be no correspondence between what the
object is and what a subject believes to be true about the object. For Hegel, any system in which the subject that knows and the object
which is known are structurally independent would make the relations
necessary for knowledge impossible. Hegel also argues that finite qualities and objects depend on other
finite things to determine them. An infinite thinking being, on the
other hand, would be more self-determining and hence most fully real.
Hegel argued that a careful analysis of the act of knowledge
would eventually lead to an understanding of the unity of subjects and
the objects in a single all-encompassing whole. In this system, experiences are not independent of the thing in itself
(as in Kant) but are manifestations grounded in a metaphysical absolute,
which is also experiential (but since it resists the experiential
subject, can be known through this resistance). Thus, our own experiences can lead us to an insight into the thing in itself. Furthermore, since reality is a unity, all knowledge is ultimately
self-knowledge, or as Hegel puts it, it is the subject being "in the
other with itself" (im Anderen bei sich selbst sein). Since all things have spirit (Geist), a philosopher can attain what he termed "absolute knowing" (absolutes Wissen), which is the knowledge that all things are ultimately manifestations of an infinite absolute spirit.
Later, in his Science of Logic
(1812–1814), Hegel further develops a metaphysics in which the real and
objective activity of thinking unfolds itself in numerous ways (as
objects and subjects). This ultimate activity of thought, which is not the activity of specific subjects, is an immediate fact, a given (vorhandenes), which is self-standing and self-organizing. In manifesting the entire world, the absolute enacts a process of
self-actualization through a grand structure or master logic, which is
what Hegel calls "reason" (Vernunft), and which he understands as a teleological reality.
The
philosophy of Arthur Schopenhauer owes much to the thought of Kant and
to that of the German idealists, which he nevertheless strongly
criticizes. Schopenhauer maintains Kant's idealist epistemology which sees even space, time and causality as mere mental representations (vorstellungen)
conditioned by the subjective mind. However, he replaces Kant's
unknowable thing-in-itself with an absolute reality underlying all ideas
that is a single irrational Will, a view that he saw as directly
opposed to Hegel's rational Spirit. This philosophy is laid out in The World as Will and Representation (WWR 1818, 2nd ed. 1844).
Schopenhauer accepts Kant's view that there can be no appearances
without there being something which appears. However, unlike Kant,
Schopenhauer writes that "we have immediate cognition of the thing in
itself when it appears to us as our own body". (WWR §6, pp. 40–1). Schopenhauer argues that, even though we do experience our own bodies
through the categories of space, time and causality, we also experience
it in another more direct and internal way through the experience of
willing. This immediate experience reveals that it is will alone which
"gives him the key to his own appearance, reveals to him the meaning and
shows him the inner workings of his essence, his deeds, his movements"
(WWR §18, p. 124). Thus, for Schopenhauer, it is desire, a "dark, dull driving", which is at the root of action, not reason. Furthermore, since this is the only form of insight we have of the
inner essence of any reality, we must apply this insight "to [the]
appearances in the inorganic [and organic] world as well." Schopenhauer
compares willing with many natural forces. As such, Will is "a name
signifying the being in itself of every thing in the world and the sole
kernel of every appearance" (WWR §23, pp. 142–3).
Because irrational Willing is the most foundational reality, life
is filled with frustration, irrationality and disappointment. This is
the metaphysical foundation of Schopenhauer's pessimistic
philosophy of life. The best we can hope for is to deny and try to
escape (however briefly) the incessant force of the Will, through art, aesthetic experience, asceticism, and compassion.
Gentile's actual idealism
Actual idealism is a form of idealism developed by Giovanni Gentile which argues that reality is the ongoing act of thinking, or in Italian "pensiero pensante" and thus, only thoughts exist. He further argued that our combined thoughts defined and produced reality. Gentile also nationalizes this idea, holding that the state is a
composition of many minds coming together to construct reality. Giovanni Gentile was a key supporter of fascism,
regarded by many as the "philosopher of fascism". His idealist theory
argued for the unity of all society under one leader, which allows it to
act as one body.
Anglo-American Idealism
Idealism was widespread in Anglo-American philosophy
during the nineteenth and twentieth centuries. It was the dominant
metaphysics in the English speaking world during the last decades of the
nineteenth century and the beginning of the twentieth century. During this time, the defenders of British idealism made significant contributions to all fields of philosophy. However, other philosophers, like McTaggart, broke from this trend and instead defended a pluralistic idealism in which the ultimate reality is a plurality of minds.
One of the early influential British idealists was Thomas Hill Green, known for his posthumous Prolegomena to Ethics.
Green argues for an idealist metaphysics in this text as a foundation
for free will and ethics. In a Kantian fashion, Green first argues that
knowledge consists in seeing relations in consciousness, and that any
sense of something being "real" or "objective" has no meaning outside of
consciousness. He then argues that experience as consciousness of related events
"cannot be explained by any natural history, properly so called" and
thus "the understanding which presents an order of nature to us is in
principle one with an understanding which constitutes that order
itself."
Green then further argues that individual human beings are aware
of an order of relations which extends beyond the bounds of their
individual mind. For Green, this greater order must be in a larger
transpersonal intelligence, while the world is "a system of related
facts" which is made possible and revealed to individual beings by the
larger intelligence. Furthermore, Green also holds that participation in the transpersonal
mind is constituted by the apprehension of a portion of the overall
order by animal organisms. As such, Green accepts the reality of biological bodies when he writes
that "in the process of our learning to know the world, an animal
organism, which has its history in time, gradually becomes the vehicle
of an eternally complete consciousness."
Another paradigmatic British absolute idealist is Francis Herbert Bradley, who affirms that "the Absolute is not many; there are no independent reals". This absolute reality "is one system, and ... its contents are nothing
but sentient experience. It will hence be a single and all-inclusive
experience, which embraces every partial diversity in concord." Bradley presents an anti-realist idealism which rejects the ultimate
reality of relations, which for him are mere appearance, "a makeshift, a
mere practical compromise, most necessary, but in the end most
indefensible."
Bradley presented his idealism in his Appearance and Reality
(1893) by arguing that the ideas we use to understand reality are
contradictory. He deconstructs numerous ideas including primary and
secondary qualities, substances and attributes, quality and relation,
space, time and causality and the self. Most famously, Bradley argued that any ultimate distinction between
qualities and relations is untenable since "qualities are nothing
without relations" since "their plurality depends on relation, and,
without that relation, they are not distinct. But, if not distinct, then
not different, and therefore not qualities." Furthermore, for Bradley, the same thing turns out to be true of
relations, and of both taken together, since for a relation to relate to
a quality, it would then require a further relation. As such, qualities
and relations are appearance, not ultimate truth, since "ultimate
reality is such that it does not contradict itself".
Even though all appearances are "not truth", it is still possible
to have true knowledge of ultimate reality, which must be a unity
beyond contradictions but which still allows for diversity. Bradley
thinks that this character of reality as a diverse unity is revealed to
us in sentient experience, since our various experiences must be
grounded and caused by some undifferentiated and pre-abstract reality.
However he also admits "our complete inability to understand this
concrete unity in detail".
American idealism
Charles Sanders Peirce
Idealism also became popular in the United States with thinkers like Charles Sanders Peirce
(1839–1914), who defended an "objective idealism" in which, as he put
it, "matter is effete mind, inveterate habits becoming physical laws". Peirce initially defended a type of representationalism alongside his form of Pragmatism which was metaphysically neutral since it is "no doctrine of metaphysics". However, in later years (after c.1905), Peirce defended an objective
idealism which held that the universe evolved from a state of maximum
spontaneous freedom (which he associated with mind) into its present
state where matter were merely "congealed" mind. In arguing for this view, he followed the classic idealist premise that states there must be a metaphysical equality (an isomorphism) between thought and being, and as such, "the root of all being is One". A key feature of Peirce's idealism is "Tychism", which he defined as "the doctrine that absolute chance is a factor of the universe." This allows for an element of chance or indeterminism in the universe which allows for cosmological evolution.
Under the influence of Peirce, it was Josiah Royce (1855–1916) who became the leading American idealist at the turn of the century. Royce's idealism incorporated aspects of Peirce's Pragmatism and is defended in his The Spirit of Modern Philosophy (1892). One of Royce's arguments for idealism is his argument from meaning, which states the possibility of there being meaning at all requires an identity between what is meant (ordinary objects) and what makes meaning (ordinary subjects).
In his The World and the Individual (2 vols, 1899 and 1901), Royce also links meaning with purpose, seeing the meaning of a term as its intended purpose. Royce was an absolute idealist who held that ultimately reality was a super-self, an absolute mind. Royce argues that for a mind to be able represent itself and its
representations (and not lead to a vicious infinite regress), it must be
complex and capacious enough, and only an absolute mind has this
capacity.
The American philosopher Brand Blanshard (1892–1987) was also a proponent of idealism who accepted a "necessary isomorphism between knowledge and its object". His idealism is most obvious in The Nature of Thought (1939), where he discusses how all perception is infused with concepts. He then argues from a coherence theory of truth that the "character of
reality" must also include coherence itself, and thus, knowledge must be
similar to what it knows. Not only that, but knowledge must be part of a single system with the
world it knows, and causal relations must be also involve logical
relations. These considerations lead to an idealism which sees the world
as system of relations that cannot be merely physical.
Pluralistic idealism
Pluralistic idealism takes the view that there are many individual minds, monads,
or processes that together underlie the existence of the observed world
and which make possible the existence of the physical universe. Pluralistic idealism does not assume the existence of a single ultimate mind or absolute as with the total monism of absolute idealism, instead it affirms an ultimate plurality of ideas or beings.
Personalism
Personalism
is the view that the individual minds of persons or selves are the
basis for ultimate reality and value and as such emphasizes the
fundamentality and inherent worth of persons. Modern personalist idealism emerged during the reaction against what
was seen as a dehumanizing impersonalism of absolute idealism, a
reaction which was led by figures like Hermann Lotze (1817–1881). Personalists affirmed personal freedom against what they saw as a
monism that lead to totalitarianism by subordinating the individual to
the collective.
Some idealistic personalists defended a theistic personalism (often influenced by Aquinas) in which reality is a society of minds ultimately dependent on a supreme person (God). Defenders of a Theistic and idealistic personalism include Borden Parker Bowne (1847–1910), Andrew Seth Pringle-Pattison (1856–1931), Edgar S. Brightman and George Holmes Howison (1834–1916). These theistic personalists emphasize the dependence of all individual minds on God.
However, other personalists like British idealist J. M. E. McTaggart and Thomas Davidson
merely argued for a community of individual minds or spirits, without
positing a supreme personal deity who creates or grounds them. Similarly, James Ward (1843–1925) was inspired by Leibniz
to defend a form of pluralistic idealism in which the universe is
composed of "psychic monads" of different levels, interacting for mutual
self-betterment.
American personalism was particularly associated with idealism and with Boston university, where Bowne (who had studied with Lotze) developed his personalist idealism and published his Personalism (1908). Bowne's students, like Edgar Sheffield Brightman, Albert C. Knudson (1873–1953), Francis J. McConnell (1871–1953), and Ralph T. Flewelling (1871–1960), continued to develop his personal idealism after his death. The "Boston personalism" tradition also influenced the later work of Peter A. Bertocci (1910–1989), as well as the ideas of Martin Luther King Jr., who studied at Boston University with personalist philosophers and was shaped by their worldview.
George Holmes Howison
meanwhile, developed his own brand of "California personalism". Howison
argued that both impersonal monistic idealism and materialism run
contrary to the experience of moral freedom,
while "personal idealism" affirms it. To deny freedom to pursue truth,
beauty, and "benignant love" is to undermine every profound human
venture, including science, morality, and philosophy. Howison, in his book The Limits of Evolution and Other Essays Illustrating the Metaphysical Theory of Personal Idealism,
developed a democratic idealism that extended all the way to God, who
instead of a monarch, was seen as the ultimate democrat in eternal
relation to other eternal persons.
Another pluralistic idealism was Thomas Davidson's (1840–1900) "apeirotheism", which he defined as "a theory of Gods infinite in number". The theory was indebted to Aristotle's view of the eternal rational soul and the nous. Identifying Aristotle's God with rational thought, Davidson argued,
contrary to Aristotle, that just as the soul cannot exist apart from the
body, God cannot exist apart from the world.
Another influential British idealist, J. M. E. McTaggart (1866–1925), defended a theory in which reality is a community of individual spirits connected by the relation of love. McTaggart defends ontological idealism through a mereological
argument which argues only spirits can be substances, as well as
through an argument for the unreality of time (a position he also
defends in The Unreality of Time).
In The Nature of Existence (1927), McTaggart's argument
relies on the premise that substances are infinitely divisible and
cannot have simple parts. Furthermore, each of their infinite parts
determines every other part. He then analyzes various characteristics of
reality such as time, matter, sensation, and cogitation and attempts to
show they cannot be real elements of real substances, but must be mere
appearances. For example, the existence of matter cannot be inferred based on
sensations, since they cannot be divided to infinity (and thus cannot be
substances). Spirits on the other hand are true infinitely divisible
substances. They have "the quality of having content, all of which is
the content of one or more selves", and know themselves through direct
perception as substances persisting through time. For McTaggart, there is a multiplicity of spirits, which are
nevertheless related to each other harmoniously through their love for
each other.
McTaggart also criticizes Hegel's view of the state in his Studies in Hegelian Cosmology (1901),
arguing that metaphysics can give very little guidance to social and
political action, just like it can give us very little guidance in other
practical matters, like engineering.
Contemporary idealism
The 20th-century British scientist Sir James Jeans wrote that "the Universe begins to look more like a great thought than like a great machine."
Today, idealism remains a minority view in Western analytic circles. In spite of this, the study of the work of the Anglo-American idealists
saw a revival in the 21st century with an increase in publications at
the turn of the century, and they are now considered to have made
important contributions to philosophy.
Several modern figures continue to defend idealism. Recent idealist philosophers include A. A. Luce (Sense without Matter, 1954), Timothy Sprigge (The Vindication of Absolute Idealism, 1984), Leslie Armour, Vittorio Hösle (Objective Idealism, 1998), John Andrew Foster (A World for Us, 2008), John A. Leslie (Infinite Minds: A Philosophical Cosmology, 2002), and Bernardo Kastrup (The Idea of the World, 2018). In 2022, Howard Robinson authored Perception and Idealism.
Both Foster and Sprigge defend idealism through an epistemic argument for the unity of the act of perception with its object. Sprigge also made an argument from grounding, which held that our phenomenal objects presuppose some noumenal
ground. As such For Sprigge, the physical world "consists in
innumerable mutually interacting centres of experience, or, what comes
to the same, of pulses and flows of experience." Thus, the noumenal ground is the totality of all experiences, which are
one "concrete universal", that resembles Bradley's absolute.
Helen Yetter-Chappell has defended nontheistic (quasi-)Berkeleyan idealism.
Analytic idealism
A
recent strand of idealist metaphysics has been developed within
analytic philosophy by Bernardo Kastrup. In his doctoral dissertation
Analytic Idealism (2019), he argues that reality is constituted by
universal consciousness and introduces the notion of dissociation as a
mechanism to explain how individual conscious agents arise within a
single underlying mind. His later work Analytic Idealism in a Nutshell has been the subject of
reviews and discussion in contemporary philosophy (e.g. Sjöstedt-Hughes
2025). Building on this approach, Bruno Tonetto’s Return to Consciousness
(2025) synthesizes consciousness-first arguments from science,
metaphysics, and cultural analysis, presenting idealism as a unifying
worldview. These contributions exemplify a small but ongoing effort to revive idealist metaphysics in analytic philosophy of mind.
Idealistic theories based on 20th-century science
Idealist notions took a strong hold among physicists of the early 20th century confronted with the paradoxes of quantum physics and the theory of relativity.
Arthur Eddington, a British astrophysicist of the early 20th century, wrote in his book The Nature of the Physical World
that the stuff of the world is mind-stuff, adding that "The mind-stuff
of the world is, of course, something more general than our individual
conscious minds." Ian Barbour, in his book Issues in Science and Religion, cites Arthur Eddington's The Nature of the Physical World
(1928) as a text that argues The Heisenberg Uncertainty Principles
provides a scientific basis for "the defense of the idea of human
freedom" and his Science and the Unseen World (1929) for support of philosophical idealism "the thesis that reality is basically mental."
The physicist Sir James Jeans
wrote: "The stream of knowledge is heading towards a non-mechanical
reality; the Universe begins to look more like a great thought than like
a great machine. Mind no longer appears to be an accidental intruder
into the realm of matter... we ought rather hail it as the creator and
governor of the realm of matter."
The chemist Ernest Lester Smith, a member of the occult movement Theosophy, wrote a book Intelligence Came First
(1975) in which he claimed that consciousness is a fact of nature and
that the cosmos is grounded in and pervaded by mind and intelligence.
Moore famously critiqued idealism and defended realism in The Refutation of Idealism (1903), and A Defence of Common Sense (1925). In the Refutation, Moore argues that arguments for idealism most often rely on the premise that to be is to be perceived (esse est percipi),
but that if this is true "how can we infer that anything whatever, let
alone everything is an inseparable aspect of any experience?". Bertrand Russell's popular 1912 book The Problems of Philosophy also contained a similar critique. Their main objection is that idealists falsely presuppose that the
mind's relation to any object is a necessary condition for the existence
of the object. Russell thinks this fallacy fails to make "the
distinction between act and object in our apprehending of things" (1912
[1974: 42]). Guyer et al. write that the success of these arguments might be
controversial and that "the charge that they simply conflate knowledge
and object hardly seems to do justice to the elaborate arguments of the
late nineteenth-century idealists." It also relies on a realist epistemology in which knowledge stands "in
an immediate relation to an independent individual object".
Regarding positive arguments, Moore's most famous argument for the existence of external matter (found in Proof of an External World, 1939) was an epistemological argument from common sense facts, sometimes known as "Here is one hand". Idealism was also more recently critiqued in the works of Australian philosopher David Stove, and by Alan Musgrave, and John Searle.
Physicist Milton A. Rothman has written that idealism is incompatible with science and is not considered an empirical system of knowledge unlike realism which is pragmatical and makes testable predictions. Rothman commented that "idealism saying nothing about why ten different
observers in different parts of the world measure the speed of light to
be the same. If the light beam exists only a construct in my mind, then
how does an experimenter in Moscow always get the same result that I do
in, say Princeton".
Philosopher and physicist Mario Bunge has written that idealistic thinking is often found in pseudosciences as it postulates immaterial entities that disregard scientific laws.
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