In logic, statistical inference, and supervised learning,
transduction or transductive inference is reasoning from
observed, specific (training) cases to specific (test) cases. In contrast,
induction is reasoning from observed training cases
to general rules, which are then applied to the test cases. The distinction is
most interesting in cases where the predictions of the transductive model are
not achievable by any inductive model. Note that this is caused by transductive
inference on different test sets producing mutually inconsistent predictions.
Transduction was introduced in a computer science context by Vladimir Vapnik in the 1990s, motivated by
his view that transduction is preferable to induction since, according to him, induction requires
solving a more general problem (inferring a function) before solving a more
specific problem (computing outputs for new cases): "When solving a problem of
interest, do not solve a more general problem as an intermediate step. Try to
get the answer that you really need but not a more general one."
An example of learning which is not inductive would be in the case of binary
classification, where the inputs tend to cluster in two groups. A large set of
test inputs may help in finding the clusters, thus providing useful information
about the classification labels. The same predictions would not be obtainable
from a model which induces a function based only on the training cases. Some
people may call this an example of the closely related semi-supervised learning, since Vapnik's motivation is quite different. An example of an algorithm in this category is the Transductive Support Vector Machine (TSVM).
A third possible motivation of transduction arises through the need
to approximate. If exact inference is computationally prohibitive, one may at
least try to make sure that the approximations are good at the test inputs. In
this case, the test inputs could come from an arbitrary distribution (not
necessarily related to the distribution of the training inputs), which wouldn't
be allowed in semi-supervised learning. An example of an algorithm falling in
this category is the Bayesian Committee Machine (BCM).
Historical Context
The
mode of inference from particulars to particulars, which Vapnik came to
call transduction, was already distinguished from the mode of inference
from particulars to generalizations in part III of the Cambridge
philosopher and logician W.E. Johnson's 1924 textbook, Logic. In Johnson's work, the former mode was called 'eduction' and the latter was called 'induction'. Bruno de Finetti
developed a purely subjective form of Bayesianism in which claims about
objective chances could be translated into empirically respectable
claims about subjective credences with respect to observables through
exchangeability properties. An early statement of this view can be found
in his 1937 La Prévision: ses Lois Logiques, ses Sources Subjectives and a mature statement in his 1970 Theory of Probability.
Within de Finetti's subjective Bayesian framework, all inductive
inference is ultimately inference from particulars to particulars.
Example problem
The following example problem contrasts some of the unique properties of transduction against induction.
A collection of points is given, such that some of the points are
labeled (A, B, or C), but most of the points are unlabeled (?). The
goal is to predict appropriate labels for all of the unlabeled points.
The inductive approach to solving this problem is to use the labeled points to train a supervised learning
algorithm, and then have it predict labels for all of the unlabeled
points. With this problem, however, the supervised learning algorithm
will only have five labeled points to use as a basis for building a
predictive model. It will certainly struggle to build a model that
captures the structure of this data. For example, if a nearest-neighbor
algorithm is used, then the points near the middle will be labeled "A"
or "C", even though it is apparent that they belong to the same cluster
as the point labeled "B".
Transduction has the advantage of being able to consider all of
the points, not just the labeled points, while performing the labeling
task. In this case, transductive algorithms would label the unlabeled
points according to the clusters to which they naturally belong. The
points in the middle, therefore, would most likely be labeled "B",
because they are packed very close to that cluster.
An advantage of transduction is that it may be able to make
better predictions with fewer labeled points, because it uses the
natural breaks found in the unlabeled points. One disadvantage of
transduction is that it builds no predictive model. If a previously
unknown point is added to the set, the entire transductive algorithm
would need to be repeated with all of the points in order to predict a
label. This can be computationally expensive if the data is made
available incrementally in a stream. Further, this might cause the
predictions of some of the old points to change (which may be good or
bad, depending on the application). A supervised learning algorithm, on
the other hand, can label new points instantly, with very little
computational cost.
Transduction algorithms
Transduction
algorithms can be broadly divided into two categories: those that seek
to assign discrete labels to unlabeled points, and those that seek to
regress continuous labels for unlabeled points. Algorithms that seek to
predict discrete labels tend to be derived by adding partial supervision
to a clustering algorithm. Two classes of algorithms can be used: flat clustering and hierarchical clustering.
The latter can be further subdivided into two categories: those that
cluster by partitioning, and those that cluster by agglomerating.
Algorithms that seek to predict continuous labels tend to be derived by
adding partial supervision to a manifold learning algorithm.
Partitioning transduction
Partitioning
transduction can be thought of as top-down transduction. It is a
semi-supervised extension of partition-based clustering. It is typically
performed as follows:
Consider the set of all points to be one large partition.
While any partition P contains two points with conflicting labels:
Partition P into smaller partitions.
For each partition P:
Assign the same label to all of the points in P.
Of course, any reasonable partitioning technique could be used with this algorithm. Max flow min cut partitioning schemes are very popular for this purpose.
Agglomerative transduction
Agglomerative
transduction can be thought of as bottom-up transduction. It is a
semi-supervised extension of agglomerative clustering. It is typically
performed as follows:
Compute the pair-wise distances, D, between all the points.
Sort D in ascending order.
Consider each point to be a cluster of size 1.
For each pair of points {a,b} in D:
If (a is unlabeled) or (b is unlabeled) or (a and b have the same label)
Merge the two clusters that contain a and b.
Label all points in the merged cluster with the same label.
Manifold transduction
Manifold-learning-based transduction is still a very young field of research.
Philosophy ('love of wisdom' in Ancient Greek) is a systematic study of general and fundamental questions concerning topics like existence, reason, knowledge, value, mind, and language. It is a rational and critical inquiry that reflects on its own methods and assumptions.
Historically, many of the individual sciences, such as physics and psychology,
formed part of philosophy. However, they are considered separate
academic disciplines in the modern sense of the term. Influential
traditions in the history of philosophy include Western, Arabic–Persian, Indian, and Chinese philosophy. Western philosophy originated in Ancient Greece
and covers a wide area of philosophical subfields. A central topic in
Arabic–Persian philosophy is the relation between reason and revelation. Indian philosophy combines the spiritual problem of how to reach enlightenment
with the exploration of the nature of reality and the ways of arriving
at knowledge. Chinese philosophy focuses principally on practical issues
in relation to right social conduct, government, and self-cultivation.
The word philosophy comes from the Ancient Greek words φίλος (philos) 'love' and σοφία (sophia) 'wisdom.' Some sources say that the term was coined by the pre-Socratic philosopher Pythagoras, but this is not certain.
The word entered the English language primarily from Old French and Anglo-Norman starting around 1175 CE. The French philosophie is itself a borrowing from the Latin philosophia. The term philosophy acquired the meanings of "advanced study of the speculative subjects (logic, ethics, physics, and metaphysics)",
"deep wisdom consisting of love of truth and virtuous living",
"profound learning as transmitted by the ancient writers", and "the
study of the fundamental nature of knowledge, reality, and existence, and the basic limits of human understanding".
Before the modern age, the term philosophy was used in a wide sense. It included most forms of rational inquiry, such as the individual sciences, as its subdisciplines. For instance, natural philosophy was a major branch of philosophy. This branch of philosophy encompassed a wide range of fields, including disciplines like physics, chemistry, and biology. An example of this usage is the 1687 book Philosophiæ Naturalis Principia Mathematica by Isaac Newton. This book referred to natural philosophy in its title, but it is today considered a book of physics.
The meaning of philosophy changed toward the end of the
modern period when it acquired the more narrow meaning common today. In
this new sense, the term is mainly associated with philosophical
disciplines like metaphysics, epistemology, and ethics. Among other
topics, it covers the rational study of reality, knowledge, and values.
It is distinguished from other disciplines of rational inquiry such as
the empirical sciences and mathematics.
The practice of philosophy is characterized by several general
features: it is a form of rational inquiry, it aims to be systematic,
and it tends to critically reflect on its own methods and
presuppositions.
It requires attentively thinking long and carefully about the
provocative, vexing, and enduring problems central to the human
condition.
The philosophical pursuit of wisdom involves asking general and
fundamental questions. It often does not result in straightforward
answers but may help a person to better understand the topic, examine
their life, dispel confusion, and overcome prejudices and self-deceptive
ideas associated with common sense. For example, Socrates stated that "the unexamined life is not worth living" to highlight the role of philosophical inquiry in understanding one's own existence. And according to Bertrand Russell,
"the man who has no tincture of philosophy goes through life imprisoned
in the prejudices derived from common sense, from the habitual beliefs
of his age or his nation, and from convictions which have grown up in
his mind without the cooperation or consent of his deliberate reason."
Attempts to provide more precise definitions of philosophy are controversial and are studied in metaphilosophy.
Some approaches argue that there is a set of essential features shared
by all parts of philosophy. Others see only weaker family resemblances
or contend that it is merely an empty blanket term. Precise definitions are often only accepted by theorists belonging to a certain philosophical movement
and are revisionistic according to Søren Overgaard et al. in that many
presumed parts of philosophy would not deserve the title "philosophy" if
they were true.
Some definitions characterize philosophy in relation to its
method, like pure reasoning. Others focus on its topic, for example, as
the study of the biggest patterns of the world as a whole or as the
attempt to answer the big questions. Such an approach is pursued by Immanuel Kant,
who holds that the task of philosophy is united by four questions:
"What can I know?"; "What should I do?"; "What may I hope?"; and "What
is the human being?"
Both approaches have the problem that they are usually either too wide,
by including non-philosophical disciplines, or too narrow, by excluding
some philosophical sub-disciplines.
Many definitions of philosophy emphasize its intimate relation to science. In this sense, philosophy is sometimes understood as a proper science in its own right. According to some naturalistic philosophers, such as W. V. O. Quine,
philosophy is an empirical yet abstract science that is concerned with
wide-ranging empirical patterns instead of particular observations.
Science-based definitions usually face the problem of explaining why
philosophy in its long history has not progressed to the same extent or
in the same way as the sciences.
This problem is avoided by seeing philosophy as an immature or
provisional science whose subdisciplines cease to be philosophy once
they have fully developed. In this sense, philosophy is sometimes described as "the midwife of the sciences".
Other definitions focus on the contrast between science and
philosophy. A common theme among many such conceptions is that
philosophy is concerned with meaning, understanding, or the clarification of language. According to one view, philosophy is conceptual analysis, which involves finding the necessary and sufficient conditions for the application of concepts. Another definition characterizes philosophy as thinking about thinking to emphasize its self-critical, reflective nature. A further approach presents philosophy as a linguistic therapy. According to Ludwig Wittgenstein,
for instance, philosophy aims at dispelling misunderstandings to which
humans are susceptible due to the confusing structure of ordinary language.
Phenomenologists, such as Edmund Husserl, characterize philosophy as a "rigorous science" investigating essences. They practice a radical suspension
of theoretical assumptions about reality to get back to the "things
themselves", that is, as originally given in experience. They contend
that this base-level of experience provides the foundation for
higher-order theoretical knowledge, and that one needs to understand the
former to understand the latter.
An early approach found in ancient Greek and Roman philosophy is that philosophy is the spiritual practice of developing one's rational capacities. This practice is an expression of the philosopher's love of wisdom and has the aim of improving one's well-being by leading a reflective life. For example, the Stoics saw philosophy as an exercise to train the mind and thereby achieve eudaimonia and flourish in life.
As a discipline, the history of philosophy aims to provide a
systematic and chronological exposition of philosophical concepts and
doctrines. Some theorists see it as a part of intellectual history,
but it also investigates questions not covered by intellectual history
such as whether the theories of past philosophers are true and have
remained philosophically relevant.
The history of philosophy is primarily concerned with theories based on
rational inquiry and argumentation; some historians understand it in a
looser sense that includes myths, religious teachings, and proverbial lore.
Aristotle
was a major figure in ancient philosophy and developed a comprehensive
system of thought including metaphysics, logic, ethics, politics, and
natural science.
Western philosophy originated in Ancient Greece in the 6th century BCE with the pre-Socratics. They attempted to provide rational explanations of the cosmos as a whole. The philosophy following them was shaped by Socrates (469–399 BCE), Plato (427–347 BCE), and Aristotle (384–322 BCE). They expanded the range of topics to questions like how people should act, how to arrive at knowledge, and what the nature of reality and mind is. The later part of the ancient period was marked by the emergence of philosophical movements, for example, Epicureanism, Stoicism, Skepticism, and Neoplatonism.
The medieval period started in the 5th century CE. Its focus was on
religious topics and many thinkers used ancient philosophy to explain
and further elaborate Christian doctrines.
The Renaissance period started in the 14th century and saw a renewed interest in schools of ancient philosophy, in particular Platonism. Humanism also emerged in this period.
The modern period started in the 17th century. One of its central
concerns was how philosophical and scientific knowledge are created.
Specific importance was given to the role of reason and sensory experience. Many of these innovations were used in the Enlightenment movement to challenge traditional authorities. Several attempts to develop comprehensive systems of philosophy were made in the 19th century, for instance, by German idealism and Marxism. Influential developments in 20th-century philosophy were the emergence and application of formal logic, the focus on the role of language as well as pragmatism, and movements in continental philosophy like phenomenology, existentialism, and post-structuralism.
The 20th century saw a rapid expansion of academic philosophy in terms
of the number of philosophical publications and philosophers working at academic institutions. There was also a noticeable growth in the number of female philosophers, but they still remained underrepresented.
Arabic–Persian philosophy arose in the early 9th century CE as a response to discussions in the Islamic theological tradition.
Its classical period lasted until the 12th century CE and was strongly
influenced by ancient Greek philosophers. It employed their ideas to
elaborate and interpret the teachings of the Quran.
Al-Kindi
(801–873 CE) is usually regarded as the first philosopher of this
tradition. He translated and interpreted many works of Aristotle and
Neoplatonists in his attempt to show that there is a harmony between reason and faith. Avicenna
(980–1037 CE) also followed this goal and developed a comprehensive
philosophical system to provide a rational understanding of reality
encompassing science, religion, and mysticism. Al-Ghazali
(1058–1111 CE) was a strong critic of the idea that reason can arrive
at a true understanding of reality and God. He formulated a detailed critique of philosophy and tried to assign philosophy a more limited place besides the teachings of the Quran and mystical insight. Following Al-Ghazali and the end of the classical period, the influence of philosophical inquiry waned. Mulla Sadra (1571–1636 CE) is often regarded as one of the most influential philosophers of the subsequent period.
The increasing influence of Western thought and institutions in the
19th and 20th centuries gave rise to the intellectual movement of Islamic modernism, which aims to understand the relation between traditional Islamic beliefs and modernity.
One of the distinguishing features of Indian philosophy is that it
integrates the exploration of the nature of reality, the ways of
arriving at knowledge, and the spiritual question of how to reach enlightenment. It started around 900 BCE when the Vedas were written. They are the foundational scriptures of Hinduism and contemplate issues concerning the relation between the self and ultimate reality as well as the question of how souls are reborn based on their past actions. This period also saw the emergence of non-Vedic teachings, like Buddhism and Jainism. Buddhism was founded by Gautama Siddhartha (563–483 BCE), who challenged the Vedic idea of a permanent self and proposed a path to liberate oneself from suffering. Jainism was founded by Mahavira (599–527 BCE), who emphasized non-violence as well as respect toward all forms of life.
The subsequent classical period started roughly 200 BCE and was characterized by the emergence of the six orthodox schools of Hinduism: Nyāyá, Vaiśeṣika, Sāṃkhya, Yoga, Mīmāṃsā, and Vedanta. The school of Advaita Vedanta developed later in this period. It was systematized by Adi Shankara (c. 700–750 CE), who held that everything is one and that the impression of a universe consisting of many distinct entities is an illusion. A slightly different perspective was defended by Ramanuja (1017–1137 CE),[c] who founded the school of Vishishtadvaita Vedanta and argued that individual entities are real as aspects or parts of the underlying unity. He also helped to popularize the Bhakti movement, which taught devotion toward the divine as a spiritual path and lasted until the 17th to 18th centuries CE. The modern period began roughly 1800 CE and was shaped by encounters with Western thought. Philosophers tried to formulate comprehensive systems to harmonize diverse philosophical and religious teachings. For example, Swami Vivekananda
(1863–1902 CE) used the teachings of Advaita Vedanta to argue that all
the different religions are valid paths toward the one divine.
The teachings of Confucius on ethics and society shaped subsequent Chinese philosophy.
Chinese philosophy is particularly interested in practical questions associated with right social conduct, government, and self-cultivation. Many schools of thought
emerged in the 6th century BCE in competing attempts to resolve the
political turbulence of that period. The most prominent among them were Confucianism and Daoism. Confucianism was founded by Confucius (551–479 BCE). It focused on different forms of moral virtues and explored how they lead to harmony in society. Daoism was founded by Laozi (6th century BCE) and examined how humans can live in harmony with nature by following the Dao or the natural order of the universe. Other influential early schools of thought were Mohism, which developed an early form of altruistic consequentialism, and Legalism, which emphasized the importance of a strong state and strict laws.
Buddhism was introduced to China in the 1st century CE and diversified into new forms of Buddhism. Starting in the 3rd century CE, the school of Xuanxue emerged. It interpreted earlier Daoist works with a specific emphasis on metaphysical explanations. Neo-Confucianism developed in the 11th century CE. It systematized previous Confucian teachings and sought a metaphysical foundation of ethics.
The modern period in Chinese philosophy began in the early 20th century
and was shaped by the influence of and reactions to Western philosophy.
The emergence of Chinese Marxism—which focused on class struggle, socialism, and communism—resulted in a significant transformation of the political landscape. Another development was the emergence of New Confucianism,
which aims to modernize and rethink Confucian teachings to explore
their compatibility with democratic ideals and modern science.
Other traditions
Traditional Japanese philosophy assimilated and synthesized ideas from different traditions, including the indigenous Shinto
religion and Chinese and Indian thought in the forms of Confucianism
and Buddhism, both of which entered Japan in the 6th and 7th centuries.
Its practice is characterized by active interaction with reality rather
than disengaged examination. Neo-Confucianism became an influential school of thought in the 16th century and the following Edo period and prompted a greater focus on language and the natural world. The Kyoto School
emerged in the 20th century and integrated Eastern spirituality with
Western philosophy in its exploration of concepts like absolute
nothingness (zettai-mu), place (basho), and the self.
Latin American philosophy in the pre-colonial period was practiced by indigenous civilizations and explored questions concerning the nature of reality and the role of humans. It has similarities to indigenous North American philosophy, which covered themes such as the interconnectedness of all things. Latin American philosophy during the colonial period, starting around 1550, was dominated by religious philosophy in the form of scholasticism. Influential topics in the post-colonial period were positivism, the philosophy of liberation, and the exploration of identity and culture.
Early African philosophy, like Ubuntu philosophy, was focused on community, morality, and ancestral ideas. Systematic African philosophy emerged at the beginning of the 20th century. It discusses topics such as ethnophilosophy, négritude, pan-Africanism, Marxism, postcolonialism, the role of cultural identity, and the critique of Eurocentrism.
Philosophical questions can be grouped into several branches. These
groupings allow philosophers to focus on a set of similar topics and
interact with other thinkers who are interested in the same questions.
Epistemology, ethics, logic, and metaphysics are sometimes listed as the
main branches.
There are many other subfields besides them and the different divisions
are neither exhaustive nor mutually exclusive. For example, political
philosophy, ethics, and aesthetics are sometimes linked under the general heading of value theory as they investigate normative or evaluative aspects.
Furthermore, philosophical inquiry sometimes overlaps with other
disciplines in the natural and social sciences, religion, and
mathematics.
Epistemology is the branch of philosophy that studies knowledge. It is also known as theory of knowledge
and aims to understand what knowledge is, how it arises, what its
limits are, and what value it has. It further examines the nature of truth, belief, justification, and rationality.
Some of the questions addressed by epistemologists include "By what
method(s) can one acquire knowledge?"; "How is truth established?"; and
"Can we prove causal relations?"
Epistemology is primarily interested in declarative knowledge or knowledge of facts, like knowing that Princess Diana died in 1997. But it also investigates practical knowledge, such as knowing how to ride a bicycle, and knowledge by acquaintance, for example, knowing a celebrity personally.
One area in epistemology is the analysis of knowledge.
It assumes that declarative knowledge is a combination of different
parts and attempts to identify what those parts are. An influential
theory in this area claims that knowledge has three components: it is a belief that is justified and true. This theory is controversial and the difficulties associated with it are known as the Gettier problem.
Alternative views state that knowledge requires additional components,
like the absence of luck; different components, like the manifestation
of cognitive virtues instead of justification; or they deny that knowledge can be analyzed in terms of other phenomena.
Another area in epistemology asks how people acquire knowledge. Often-discussed sources of knowledge are perception, introspection, memory, inference, and testimony. According to empiricists, all knowledge is based on some form of experience. Rationalists reject this view and hold that some forms of knowledge, like innate knowledge, are not acquired through experience. The regress problem
is a common issue in relation to the sources of knowledge and the
justification they offer. It is based on the idea that beliefs require
some kind of reason or evidence to be justified. The problem is that the
source of justification may itself be in need of another source of
justification. This leads to an infinite regress or circular reasoning. Foundationalists avoid this conclusion by arguing that some sources can provide justification without requiring justification themselves. Another solution is presented by coherentists, who state that a belief is justified if it coheres with other beliefs of the person.
Many discussions in epistemology touch on the topic of philosophical skepticism,
which raises doubts about some or all claims to knowledge. These doubts
are often based on the idea that knowledge requires absolute certainty
and that humans are unable to acquire it.
"The
utilitarian doctrine is, that happiness is desirable, and the only
thing desirable, as an end; all other things being only desirable as
means to that end." — John Stuart Mill, Utilitarianism (1863)
Ethics, also known as moral philosophy, studies what constitutes right conduct. It is also concerned with the moral evaluation of character traits and institutions. It explores what the standards of morality are and how to live a good life.
Philosophical ethics addresses such basic questions as "Are moral
obligations relative?"; "Which has priority: well-being or obligation?";
and "What gives life meaning?"
The main branches of ethics are meta-ethics, normative ethics, and applied ethics.
Meta-ethics asks abstract questions about the nature and sources of
morality. It analyzes the meaning of ethical concepts, like right action and obligation. It also investigates whether ethical theories can be true in an absolute sense and how to acquire knowledge of them.
Normative ethics encompasses general theories of how to distinguish
between right and wrong conduct. It helps guide moral decisions by
examining what moral obligations and rights people have. Applied ethics
studies the consequences of the general theories developed by normative
ethics in specific situations, for example, in the workplace or for
medical treatments.
Within contemporary normative ethics, consequentialism, deontology, and virtue ethics are influential schools of thought. Consequentialists judge actions based on their consequences. One such view is utilitarianism, which argues that actions should increase overall happiness while minimizing suffering. Deontologists
judge actions based on whether they follow moral duties, such as
abstaining from lying or killing. According to them, what matters is
that actions are in tune with those duties and not what consequences
they have. Virtue theorists judge actions based on how the moral
character of the agent is expressed. According to this view, actions
should conform to what an ideally virtuous agent would do by manifesting
virtues like generosity and honesty.
Logic is the study of correct reasoning. It aims to understand how to distinguish good from bad arguments. It is usually divided into formal and informal logic. Formal logic uses artificial languages
with a precise symbolic representation to investigate arguments. In its
search for exact criteria, it examines the structure of arguments to
determine whether they are correct or incorrect. Informal logic uses
non-formal criteria and standards to assess the correctness of
arguments. It relies on additional factors such as content and context.
Logic examines a variety of arguments. Deductive arguments are mainly studied by formal logic. An argument is deductively valid if the truth of its premises ensures the truth of its conclusion. Deductively valid arguments follow a rule of inference, like modus ponens, which has the following logical form: "p; if p then q; therefore q".
An example is the argument "today is Sunday; if today is Sunday then I
don't have to go to work today; therefore I don't have to go to work
today".
The premises of non-deductive arguments also support their
conclusion, although this support does not guarantee that the conclusion
is true. One form is inductive reasoning.
It starts from a set of individual cases and uses generalization to
arrive at a universal law governing all cases. An example is the
inference that "all ravens are black" based on observations of many
individual black ravens. Another form is abductive reasoning.
It starts from an observation and concludes that the best explanation
of this observation must be true. This happens, for example, when a
doctor diagnoses a disease based on the observed symptoms.
Logic also investigates incorrect forms of reasoning. They are called fallacies and are divided into formal and informal fallacies based on whether the source of the error lies only in the form of the argument or also in its content and context.
Metaphysics is the study of the most general features of reality, such as existence, objects and their properties, wholes and their parts, space and time, events, and causation. There are disagreements about the precise definition of the term and its meaning has changed throughout the ages. Metaphysicians attempt to answer basic questions including "Why is there something rather than nothing?"; "Of what does reality ultimately consist?"; and "Are humans free?"
Metaphysics is sometimes divided into general metaphysics and
specific or special metaphysics. General metaphysics investigates being
as such. It examines the features that all entities have in common.
Specific metaphysics is interested in different kinds of being, the
features they have, and how they differ from one another.
An important area in metaphysics is ontology. Some theorists identify it with general metaphysics. Ontology investigates concepts like being, becoming, and reality. It studies the categories of being and asks what exists on the most fundamental level. Another subfield of metaphysics is philosophical cosmology.
It is interested in the essence of the world as a whole. It asks
questions including whether the universe has a beginning and an end and
whether it was created by something else.
A key topic in metaphysics concerns the question of whether
reality only consists of physical things like matter and energy.
Alternative suggestions are that mental entities (such as souls and experiences) and abstract entities (such as numbers) exist apart from physical things. Another topic in metaphysics concerns the problem of identity. One question is how much an entity can change while still remaining the same entity. According to one view, entities have essential and accidental features. They can change their accidental features but they cease to be the same entity if they lose an essential feature. A central distinction in metaphysics is between particulars and universals.
Universals, like the color red, can exist at different locations at the
same time. This is not the case for particulars including individual
persons or specific objects. Other metaphysical questions are whether the past fully determines the present and what implications this would have for the existence of free will.
There are many other subfields of philosophy besides its core
branches. Some of the most prominent are aesthetics, philosophy of
language, philosophy of mind, philosophy of religion, philosophy of
science, and political philosophy.
Aesthetics in the philosophical sense is the field that studies the nature and appreciation of beauty and other aesthetic properties, like the sublime. Although it is often treated together with the philosophy of art, aesthetics is a broader category that encompasses other aspects of experience, such as natural beauty. In a more general sense, aesthetics is "critical reflection on art, culture, and nature". A key question in aesthetics is whether beauty is an objective feature of entities or a subjective aspect of experience. Aesthetic philosophers also investigate the nature of aesthetic experiences and judgments. Further topics include the essence of works of art and the processes involved in creating them.
The philosophy of language studies the nature and function of language. It examines the concepts of meaning, reference, and truth. It aims to answer questions such as how words are related to things and how language affects human thought and understanding. It is closely related to the disciplines of logic and linguistics. The philosophy of language rose to particular prominence in the early 20th century in analytic philosophy due to the works of Frege
and Russell. One of its central topics is to understand how sentences
get their meaning. There are two broad theoretical camps: those
emphasizing the formal truth conditions of sentences
and those investigating circumstances that determine when it is
suitable to use a sentence, the latter of which is associated with speech act theory.
The philosophy of mind studies the nature of mental phenomena and how they are related to the physical world. It aims to understand different types of conscious and unconsciousmental states, like beliefs, desires, intentions, feelings, sensations, and free will.
An influential intuition in the philosophy of mind is that there is a
distinction between the inner experience of objects and their existence
in the external world. The mind-body problem is the problem of explaining how these two types of thing—mind and matter—are related. The main traditional responses are materialism, which assumes that matter is more fundamental; idealism, which assumes that mind is more fundamental; and dualism, which assumes that mind and matter are distinct types of entities. In contemporary philosophy, another common view is functionalism, which understands mental states in terms of the functional or causal roles they play. The mind-body problem is closely related to the hard problem of consciousness, which asks how the physical brain can produce qualitatively subjective experiences.
The philosophy of religion investigates the basic concepts, assumptions, and arguments associated with religion. It critically reflects on what religion is, how to define the divine, and whether one or more gods exist. It also includes the discussion of worldviews that reject religious doctrines. Further questions addressed by the philosophy of religion are: "How are we to interpret religious language, if not literally?"; "Is divine omniscience compatible with free will?";
and, "Are the great variety of world religions in some way compatible
in spite of their apparently contradictory theological claims?" It includes topics from nearly all branches of philosophy. It differs from theology
since theological debates typically take place within one religious
tradition, whereas debates in the philosophy of religion transcend any
particular set of theological assumptions.
The philosophy of science
examines the fundamental concepts, assumptions, and problems associated
with science. It reflects on what science is and how to distinguish it
from pseudoscience.
It investigates the methods employed by scientists, how their
application can result in knowledge, and on what assumptions they are
based. It also studies the purpose and implications of science. Some of its questions are "What counts as an adequate explanation?"; "Is a scientific law anything more than a description of a regularity?"; and "Can some special sciences be explained entirely in the terms of a more general science?" It is a vast field that is commonly divided into the philosophy of the natural sciences and the philosophy of the social sciences,
with further subdivisions for each of the individual sciences under
these headings. How these branches are related to one another is also a
question in the philosophy of science. Many of its philosophical issues
overlap with the fields of metaphysics or epistemology.
Political philosophy
is the philosophical inquiry into the fundamental principles and ideas
governing political systems and societies. It examines the basic
concepts, assumptions, and arguments in the field of politics. It investigates the nature and purpose of government and compares its different forms. It further asks under what circumstances the use of political power is legitimate, rather than a form of simple violence. In this regard, it is concerned with the distribution of political power, social and material goods, and legal rights. Other topics are justice, liberty, equality, sovereignty, and nationalism. Political philosophy involves a general inquiry into normative matters and differs in this respect from political science, which aims to provide empirical descriptions of actually existing states. Political philosophy is often treated as a subfield of ethics. Influential schools of thought in political philosophy are liberalism, conservativism, socialism, and anarchism.
Methods of philosophy are ways of conducting philosophical inquiry.
They include techniques for arriving at philosophical knowledge and
justifying philosophical claims as well as principles used for choosing
between competing theories.
A great variety of methods have been employed throughout the history of
philosophy. Many of them differ significantly from the methods used in
the natural sciences in that they do not use experimental data obtained through measuring equipment.
The choice of one's method usually has important implications both for
how philosophical theories are constructed and for the arguments cited
for or against them. This choice is often guided by epistemological considerations about what constitutes philosophical evidence.
Methodological disagreements can cause conflicts among
philosophical theories or about the answers to philosophical questions.
The discovery of new methods has often had important consequences both
for how philosophers conduct their research and for what claims they
defend.
Some philosophers engage in most of their theorizing using one
particular method while others employ a wider range of methods based on
which one fits the specific problem investigated best.
Conceptual analysis is a common method in analytic philosophy. It
aims to clarify the meaning of concepts by analyzing them into their
component parts. Another method often employed in analytic philosophy is based on common sense.
It starts with commonly accepted beliefs and tries to draw unexpected
conclusions from them, which it often employs in a negative sense to
criticize philosophical theories that are too far removed from how the
average person sees the issue. It is similar to how ordinary language philosophy approaches philosophical questions by investigating how ordinary language is used.
The trolley problem
is a thought experiment that investigates the moral difference between
doing and allowing harm. This issue is explored in an imaginary
situation in which a person can sacrifice a single person by redirecting
a trolley to save a group of people.
Various methods in philosophy give particular importance to intuitions, that is, non-inferential impressions about the correctness of specific claims or general principles. For example, they play an important role in thought experiments, which employ counterfactual thinking
to evaluate the possible consequences of an imagined situation. These
anticipated consequences can then be used to confirm or refute
philosophical theories. The method of reflective equilibrium also employs intuitions. It seeks to form a coherent
position on a certain issue by examining all the relevant beliefs and
intuitions, some of which often have to be deemphasized or reformulated
to arrive at a coherent perspective.
Pragmatists stress the significance of concrete practical consequences for assessing whether a philosophical theory is true. According to the pragmatic maxim as formulated by Charles Sanders Peirce,
the idea a person has of an object is nothing more than the totality of
practical consequences they associate with this object. Pragmatists
have also used this method to expose disagreements as merely verbal,
that is, to show they make no genuine difference on the level of
consequences.
Phenomenologists seek knowledge of the realm of appearance and
the structure of human experience. They insist upon the first-personal
character of all experience and proceed by suspending theoretical
judgments about the external world. This technique of phenomenological
reduction is known as "bracketing" or epoché. The goal is to give an unbiased description of the appearances of things.
Methodological naturalism
places great emphasis on the empirical approach and the resulting
theories found in the natural sciences. In this way, it contrasts with
methodologies that give more weight to pure reasoning and introspection.
Relation to other fields
Philosophy is closely related to many other fields. It is sometimes
understood as a metadiscipline that clarifies their nature and limits.
It does this by critically examining their basic concepts, background
assumptions, and methods. In this regard, it plays a key role in
providing an interdisciplinary
perspective. It bridges the gap between different disciplines by
analyzing which concepts and problems they have in common. It shows how
they overlap while also delimiting their scope. Historically, most of the individual sciences originated from philosophy.
The influence of philosophy is felt in several fields that require difficult practical decisions. In medicine, philosophical considerations related to bioethics affect issues like whether an embryo is already a person and under what conditions abortion
is morally permissible. A closely related philosophical problem is how
humans should treat other animals, for instance, whether it is
acceptable to use non-human animals as food or for research experiments. In relation to business
and professional life, philosophy has contributed by providing ethical
frameworks. They contain guidelines on which business practices are
morally acceptable and cover the issue of corporate social responsibility.
Philosophical inquiry is relevant to many fields that are
concerned with what to believe and how to arrive at evidence for one's
beliefs.
This is a key issue for the sciences, which have as one of their prime
objectives the creation of scientific knowledge. Scientific knowledge is
based on empirical evidence but it is often not clear whether empirical observations are neutral or already include theoretical assumptions. A closely connected problem is whether the available evidence is sufficient to decide between competing theories. Epistemological problems in relation to the law include what counts as evidence and how much evidence is required to find a person guilty of a crime. A related issue in journalism is how to ensure truth and objectivity when reporting on events.
In the fields of theology
and religion, there are many doctrines associated with the existence
and nature of God as well as rules governing correct behavior. A key
issue is whether a rational person should believe these doctrines, for
example, whether revelation in the form of holy books and religious experiences of the divine are sufficient evidence for these beliefs.
Judith Butler is one of the philosophers responsible for the cultural influence of philosophy on the feminist movement.
Philosophy in the form of logic has been influential in the fields of mathematics and computer science. Further fields influenced by philosophy include psychology, sociology, linguistics, education, and the arts.
The close relation between philosophy and other fields in the
contemporary period is reflected in the fact that many philosophy
graduates go on to work in related fields rather than in philosophy
itself.
The idea that philosophy is useful for many aspects of life and
society is sometimes rejected. According to one such view, philosophy is
mainly undertaken for its own sake and does not make significant
contributions to existing practices or external goals.
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