Search This Blog

Sunday, May 9, 2021

Relativism

From Wikipedia, the free encyclopedia

Relativism is a family of philosophical views which deny claims to objectivity within a particular domain and assert that facts in that domain are relative to the perspective of an observer or the context in which they are assessed. There are many different forms of relativism, with a great deal of variation in scope and differing degrees of controversy among them. Moral relativism encompasses the differences in moral judgments among people and cultures. Epistemic relativism holds that there are no absolute facts regarding norms of belief, justification, or rationality, and that there are only relative ones. Alethic relativism is the doctrine that there are no absolute truths, i.e., that truth is always relative to some particular frame of reference, such as a language or a culture (cultural relativism). Some forms of relativism also bear a resemblance to philosophical skepticism. Descriptive relativism seeks to describe the differences among cultures and people without evaluation, while normative relativism evaluates the morality or truthfulness of views within a given framework.

Forms of relativism

Anthropological versus philosophical relativism

Anthropological relativism refers to a methodological stance, in which the researcher suspends (or brackets) his or her own cultural prejudice while trying to understand beliefs or behaviors in their contexts. This has become known as methodological relativism, and concerns itself specifically with avoiding ethnocentrism or the application of one's own cultural standards to the assessment of other cultures. This is also the basis of the so-called "emic" and "etic" distinction, in which:

  • An emic or insider account of behavior is a description of a society in terms that are meaningful to the participant or actor's own culture; an emic account is therefore culture-specific, and typically refers to what is considered "common sense" within the culture under observation.
  • An etic or outsider account is a description of a society by an observer, in terms that can be applied to other cultures; that is, an etic account is culturally neutral, and typically refers to the conceptual framework of the social scientist. (This is complicated when it is scientific research itself that is under study, or when there is theoretical or terminological disagreement within the social sciences.)

Philosophical relativism, in contrast, asserts that the truth of a proposition depends on the metaphysical, or theoretical frame, or the instrumental method, or the context in which the proposition is expressed, or on the person, groups, or culture who interpret the proposition.

Methodological relativism and philosophical relativism can exist independently from one another, but most anthropologists base their methodological relativism on that of the philosophical variety.

Descriptive versus normative relativism

The concept of relativism also has importance both for philosophers and for anthropologists in another way. In general, anthropologists engage in descriptive relativism ("how things are" or "how things seem"), whereas philosophers engage in normative relativism ("how things ought to be"), although there is some overlap (for example, descriptive relativism can pertain to concepts, normative relativism to truth).

Descriptive relativism assumes that certain cultural groups have different modes of thought, standards of reasoning, and so forth, and it is the anthropologist's task to describe, but not to evaluate the validity of these principles and practices of a cultural group. It is possible for an anthropologist in his or her fieldwork to be a descriptive relativist about some things that typically concern the philosopher (e.g., ethical principles) but not about others (e.g., logical principles). However, the descriptive relativist's empirical claims about epistemic principles, moral ideals and the like are often countered by anthropological arguments that such things are universal, and much of the recent literature on these matters is explicitly concerned with the extent of, and evidence for, cultural or moral or linguistic or human universals.

The fact that the various species of descriptive relativism are empirical claims, may tempt the philosopher to conclude that they are of little philosophical interest, but there are several reasons why this isn't so. First, some philosophers, notably Kant, argue that certain sorts of cognitive differences between human beings (or even all rational beings) are impossible, so such differences could never be found to obtain in fact, an argument that places a priori limits on what empirical inquiry could discover and on what versions of descriptive relativism could be true. Second, claims about actual differences between groups play a central role in some arguments for normative relativism (for example, arguments for normative ethical relativism often begin with claims that different groups in fact have different moral codes or ideals). Finally, the anthropologist's descriptive account of relativism helps to separate the fixed aspects of human nature from those that can vary, and so a descriptive claim that some important aspect of experience or thought does (or does not) vary across groups of human beings tells us something important about human nature and the human condition.

Normative relativism concerns normative or evaluative claims that modes of thought, standards of reasoning, or the like are only right or wrong relative to a framework. ‘Normative’ is meant in a general sense, applying to a wide range of views; in the case of beliefs, for example, normative correctness equals truth. This does not mean, of course, that framework-relative correctness or truth is always clear, the first challenge being to explain what it amounts to in any given case (e.g., with respect to concepts, truth, epistemic norms). Normative relativism (say, in regard to normative ethical relativism) therefore implies that things (say, ethical claims) are not simply true in themselves, but only have truth values relative to broader frameworks (say, moral codes). (Many normative ethical relativist arguments run from premises about ethics to conclusions that assert the relativity of truth values, bypassing general claims about the nature of truth, but it is often more illuminating to consider the type of relativism under question directly.)

Related and contrasting positions

Relationism is the theory that there are only relations between individual entities, and no intrinsic properties. Despite the similarity in name, it is held by some to be a position distinct from relativism—for instance, because "statements about relational properties [...] assert an absolute truth about things in the world". On the other hand, others wish to equate relativism, relationism and even relativity, which is a precise theory of relationships between physical objects: Nevertheless, "This confluence of relativity theory with relativism became a strong contributing factor in the increasing prominence of relativism".

Whereas previous investigations of science only sought sociological or psychological explanations of failed scientific theories or pathological science, the 'strong programme' is more relativistic, assessing scientific truth and falsehood equally in a historic and cultural context.

Criticisms

A common argument against relativism suggests that it inherently contradicts, refutes, or stultifies itself: the statement "all is relative" classes either as a relative statement or as an absolute one. If it is relative, then this statement does not rule out absolutes. If the statement is absolute, on the other hand, then it provides an example of an absolute statement, proving that not all truths are relative. However, this argument against relativism only applies to relativism that positions truth as relative–i.e. epistemological/truth-value relativism. More specifically, it is only extreme forms of epistemological relativism that can come in for this criticism as there are many epistemological relativists who posit that some aspects of what is regarded as factually "true" are not universal, yet still accept that other universal truths exist (e.g. gas laws or moral laws).

Another argument against relativism posits a Natural Law. Simply put, the physical universe works under basic principles: the "Laws of Nature". Some contend that a natural Moral Law may also exist, for example as argued by Richard Dawkins in The God Delusion (2006) and addressed by C. S. Lewis in "Mere Christianity" (1952). Dawkins said "I think we face an equal but much more sinister challenge from the left, in the shape of cultural relativism - the view that scientific truth is only one kind of truth and it is not to be especially privileged". Philosopher Hilary Putnam, among others, states that some forms of relativism make it impossible to believe one is in error. If there is no truth beyond an individual's belief that something is true, then an individual cannot hold their own beliefs to be false or mistaken. A related criticism is that relativizing truth to individuals destroys the distinction between truth and belief.

Views

Ancient India

Ancient Indian philosophers Mahavira (c. 599 – c. 527 BC) and Nagarjuna (c. 150 – c. 250 BC) made contributions to the development of relativist philosophy.

Sophism

Sophists are considered the founding fathers of relativism in Western philosophy. Elements of relativism emerged among the Sophists in the 5th century BC. Notably, it was Protagoras who coined the phrase, "Man is the measure of all things: of things which are, that they are, and of things which are not, that they are not." The thinking of the Sophists is mainly known through their opponent, Plato. In a paraphrase from Plato's dialogue Protagoras, Protagoras said: "What is true for you is true for you, and what is true for me is true for me."

Pyrrhonism

Pyrrhonist philosophy views relativity as a reason for philosophical skepticism, as it is one of the reasons that truth cannot be grasped. All perception is relative to a perceiver, and perception differs according to position. Hence, no particular perception can be judged as representing the truth about what is perceived. Arguments from relativity form the basis of trope 8 of the ten modes of Aenesidemus and trope 3 of the five modes of Agrippa.

Modern

Bernard Crick

Bernard Crick, a British political scientist and advocate of relativism, wrote the book In Defence of Politics (first published in 1962), suggesting the inevitability of moral conflict between people. Crick stated that only ethics could resolve such conflict, and when that occurred in public it resulted in politics. Accordingly, Crick saw the process of dispute resolution, harms reduction, mediation or peacemaking as central to all of moral philosophy. He became an important influence on the feminists and later on the Greens.

Paul Feyerabend

The philosopher of science Paul Feyerabend is often considered to be a relativist, though he denied being one.

Feyerabend argued that modern science suffers from being methodologically monistic (the belief that only a single methodology can produce scientific progress). Feyerabend summarises his case in his work Against Method with the phrase "anything goes".

In an aphorism [Feyerabend] often repeated, "potentially every culture is all cultures". This is intended to convey that world views are not hermetically closed, since their leading concepts have an "ambiguity" - better, an open-endedness - which enables people from other cultures to engage with them. [...] It follows that relativism, understood as the doctrine that truth is relative to closed systems, can get no purchase. [...] For Feyerabend, both hermetic relativism and its absolutist rival [realism] serve, in their different ways, to "devalue human existence". The former encourages that unsavoury brand of political correctness which takes the refusal to criticise "other cultures" to the extreme of condoning murderous dictatorship and barbaric practices. The latter, especially in its favoured contemporary form of "scientific realism", with the excessive prestige it affords to the abstractions of "the monster 'science'", is in bed with a politics which likewise disdains variety, richness and everyday individuality - a politics which likewise "hides" its norms behind allegedly neutral facts, "blunts choices and imposes laws".
Thomas Kuhn

Thomas Kuhn's philosophy of science, as expressed in The Structure of Scientific Revolutions is often interpreted as relativistic. He claimed that as well as progressing steadily and incrementally ("normal science"), science undergoes periodic revolutions or "paradigm shifts", leaving scientists working in different paradigms with difficulty in even communicating. Thus the truth of a claim, or the existence of a posited entity is relative to the paradigm employed. However, it isn't necessary for him to embrace relativism because every paradigm presupposes the prior, building upon itself through history and so on. This leads to there being a fundamental, incremental, and referential structure of development which is not relative but again, fundamental.

From these remarks, one thing is however certain: Kuhn is not saying that incommensurable theories cannot be compared - what they can’t be is compared in terms of a system of common measure. He very plainly says that they can be compared, and he reiterates this repeatedly in later work, in a (mostly in vain) effort to avert the crude and sometimes catastrophic misinterpretations he suffered from mainstream philosophers and post-modern relativists alike.

But Thomas Kuhn denied the accusation of being a relativist later in his postscript.

scientific development is ... a unidirectional and irreversible process. Latter scientific theories are better than earlier ones for solving puzzles ... That is not a relativist's position, and it displays the sense in which I am a convinced believer in scientific progress.

Some have argued that one can also read Kuhn's work as essentially positivist in its ontology: the revolutions he posits are epistemological, lurching toward a presumably 'better' understanding of an objective reality through the lens presented by the new paradigm. However, a number of passages in Structures do indeed appear to be distinctly relativist, and to directly challenge the notion of an objective reality and the ability of science to progress towards an ever-greater grasp of it, particularly through the process of paradigm change.

In the sciences there need not be progress of another sort. We may, to be more precise, have to relinquish the notion, explicit or implicit, that changes of paradigm carry scientists and those who learn from them closer and closer to the truth.
We are all deeply accustomed to seeing science as the one enterprise that draws constantly nearer to some goal set by nature in advance. But need there be any such goal? Can we not account for both science’s existence and its success in terms of evolution from the community’s state of knowledge at any given time? Does it really help to imagine that there is some one full, objective, true account of nature and that the proper measure of scientific achievement is the extent to which it brings us closer to that ultimate goal?
George Lakoff and Mark Johnson

George Lakoff and Mark Johnson define relativism in their book Metaphors We Live By as the rejection of both subjectivism and metaphysical objectivism in order to focus on the relationship between them, i.e. the metaphor by which we relate our current experience to our previous experience. In particular, Lakoff and Johnson characterize "objectivism" as a "straw man", and, to a lesser degree, criticize the views of Karl Popper, Kant and Aristotle.

Robert Nozick

In his book Invariances, Robert Nozick expresses a complex set of theories about the absolute and the relative. He thinks the absolute/relative distinction should be recast in terms of an invariant/variant distinction, where there are many things a proposition can be invariant with regard to or vary with. He thinks it is coherent for truth to be relative, and speculates that it might vary with time. He thinks necessity is an unobtainable notion, but can be approximated by robust invariance across a variety of conditions—although we can never identify a proposition that is invariant with regard to everything. Finally, he is not particularly warm to one of the most famous forms of relativism, moral relativism, preferring an evolutionary account.

Joseph Margolis

Joseph Margolis advocates a view he calls "robust relativism" and defends it in his books: Historied Thought, Constructed World, Chapter 4 (California, 1995) and The Truth about Relativism (Blackwells, 1991). He opens his account by stating that our logics should depend on what we take to be the nature of the sphere to which we wish to apply our logics. Holding that there can be no distinctions which are not "privileged" between the alethic, the ontic, and the epistemic, he maintains that a many valued logic just might be the most apt for aesthetics or history since, because in these practices, we are loath to hold to simple binary logic; and he also holds that many-valued logic is relativistic. (This is perhaps an unusual definition of "relativistic". Compare with his comments on "relationism"). "True" and "False" as mutually exclusive and exhaustive judgements on Hamlet, for instance, really does seem absurd. A many valued logic—"apt", "reasonable", "likely", and so on—seems intuitively more applicable to Hamlet interpretation. Where apparent contradictions arise between such interpretations, we might call the interpretations "incongruent", rather than dubbing either "false", because using many-valued logic implies that a measured value is a mixture of two extreme possibilities. Using the subset of many-valued logic, fuzzy logic, it can be said that various interpretations can be represented by membership in more than one possible truth sets simultaneously. Fuzzy logic is therefore probably the best mathematical structure for understanding "robust relativism" and has been interpreted by Bart Kosko as philosophically being related to Zen Buddhism.

It was Aristotle who held that relativism implied we should, sticking with appearances only, end up contradicting ourselves somewhere if we could apply all attributes to all ousiai (beings). Aristotle, however, made non-contradiction dependent upon his essentialism. If his essentialism is false, then so too is his ground for disallowing relativism. (Subsequent philosophers have found other reasons for supporting the principle of non-contradiction).

Beginning with Protagoras and invoking Charles Sanders Peirce, Margolis shows that the historic struggle to discredit relativism is an attempt to impose an unexamined belief in the world's essentially rigid rule-like nature. Plato and Aristotle merely attacked "relationalism"—the doctrine of true-for l or true for k, and the like, where l and k are different speakers or different worlds, or the something similar (Most philosophers would call this position "relativism"). For Margolis, "true" means true; that is, the alethic use of "true" remains untouched. However, in real world contexts, and context is ubiquitous in the real world, we must apply truth values. Here, in epistemic terms, we might retire "true" tout court as an evaluation and keep "false". The rest of our value-judgements could be graded from "extremely plausible" down to "false". Judgements which on a bivalent logic would be incompatible or contradictory are further seen as "incongruent", though one may well have more weight than the other. In short, relativistic logic is not, or need not be, the bugbear it is often presented to be. It may simply be the best type of logic to apply to certain very uncertain spheres of real experiences in the world (although some sort of logic needs to be applied to make that judgement). Those who swear by bivalent logic might simply be the ultimate keepers of the great fear of the flux.

Richard Rorty

Philosopher Richard Rorty has a somewhat paradoxical role in the debate over relativism: he is criticized for his relativistic views by many commentators, but has always denied that relativism applies to much anybody, being nothing more than a Platonic scarecrow. Rorty claims, rather, that he is a pragmatist, and that to construe pragmatism as relativism is to beg the question.

'"Relativism" is the traditional epithet applied to pragmatism by realists'
'"Relativism" is the view that every belief on a certain topic, or perhaps about any topic, is as good as every other. No one holds this view. Except for the occasional cooperative freshman, one cannot find anybody who says that two incompatible opinions on an important topic are equally good. The philosophers who get called 'relativists' are those who say that the grounds for choosing between such opinions are less algorithmic than had been thought.'
'In short, my strategy for escaping the self-referential difficulties into which "the Relativist" keeps getting himself is to move everything over from epistemology and metaphysics into cultural politics, from claims to knowledge and appeals to self-evidence to suggestions about what we should try.'

Rorty takes a deflationary attitude to truth, believing there is nothing of interest to be said about truth in general, including the contention that it is generally subjective. He also argues that the notion of warrant or justification can do most of the work traditionally assigned to the concept of truth, and that justification is relative; justification is justification to an audience, for Rorty.

In Contingency, Irony, and Solidarity he argues that the debate between so-called relativists and so-called objectivists is beside the point because they don't have enough premises in common for either side to prove anything to the other.

Nalin de Silva

In his book Mage Lokaya (My World), 1986, Nalin de Silva criticized the basis of the established western system of knowledge, and its propagation, which he refers as "domination throughout the world".He explained in this book that mind independent reality is impossible and knowledge is not found but constructed. Further he has introduced and developed the concept of "Constructive Relativism" as the basis on which knowledge is constructed relative to the sense organs, culture and the mind completely based on Avidya.

Postmodernism

The term "relativism" often comes up in debates over postmodernism, poststructuralism and phenomenology. Critics of these perspectives often identify advocates with the label "relativism". For example, the Sapir–Whorf hypothesis is often considered a relativist view because it posits that linguistic categories and structures shape the way people view the world. Stanley Fish has defended postmodernism and relativism.

These perspectives do not strictly count as relativist in the philosophical sense, because they express agnosticism on the nature of reality and make epistemological rather than ontological claims. Nevertheless, the term is useful to differentiate them from realists who believe that the purpose of philosophy, science, or literary critique is to locate externally true meanings. Important philosophers and theorists such as Michel Foucault, Max Stirner, political movements such as post-anarchism or post-Marxism can also be considered as relativist in this sense - though a better term might be social constructivist.

The spread and popularity of this kind of "soft" relativism varies between academic disciplines. It has wide support in anthropology and has a majority following in cultural studies. It also has advocates in political theory and political science, sociology, and continental philosophy (as distinct from Anglo-American analytical philosophy). It has inspired empirical studies of the social construction of meaning such as those associated with labelling theory, which defenders can point to as evidence of the validity of their theories (albeit risking accusations of performative contradiction in the process). Advocates of this kind of relativism often also claim that recent developments in the natural sciences, such as Heisenberg's uncertainty principle, quantum mechanics, chaos theory and complexity theory show that science is now becoming relativistic. However, many scientists who use these methods continue to identify as realist or post-positivist, and some sharply criticize the association.

Religious

Jainism

Mahavira (599-527 BC), the 24th Tirthankara of Jainism, developed an early philosophy regarding relativism and subjectivism known as Anekantavada.

Hinduism

Hindu religion has no theological difficulties in accepting degrees of truth in other religions. A Rig Vedic hymn states that "Truth is One, though the sages tell it variously." (Ékam sat vipra bahudā vadanti)

Buddhism

Madhyamaka Buddhism, which forms the basis for many Mahayana Buddhist schools and which was founded by Nagarjuna. Nāgārjuna taught the idea of relativity. In the Ratnāvalī, he gives the example that shortness exists only in relation to the idea of length. The determination of a thing or object is only possible in relation to other things or objects, especially by way of contrast. He held that the relationship between the ideas of "short" and "long" is not due to intrinsic nature (svabhāva). This idea is also found in the Pali Nikāyas and Chinese Āgamas, in which the idea of relativity is expressed similarly: "That which is the element of light ... is seen to exist on account of [in relation to] darkness; that which is the element of good is seen to exist on account of bad; that which is the element of space is seen to exist on account of form."

Madhyamaka Buddhism discerns two levels of truth, absolute and relative. The two truths doctrine states that there is Relative or common-sense truth, which describes our daily experience of a concrete world, and Ultimate truth, which describes the ultimate reality as sunyata, empty of concrete and inherent characteristics. The conventional truth may be interpreted as "obscurative truth" or "that which obscures the true nature" as a result. It is constituted by the appearances of mistaken awareness. Conventional truth would be the appearance that includes a duality of apprehender and apprehended, and objects perceived within that. Ultimate truths, are phenomena free from the duality of apprehender and apprehended.

Sikhism

In Sikhism the Gurus (spiritual teacher ) have propagated the message of "many paths" leading to the one God and ultimate salvation for all souls who tread on the path of righteousness. They have supported the view that proponents of all faiths can, by doing good and virtuous deeds and by remembering the Lord, certainly achieve salvation. The students of the Sikh faith are told to accept all leading faiths as possible vehicles for attaining spiritual enlightenment provided the faithful study, ponder and practice the teachings of their prophets and leaders. The holy book of the Sikhs called the Sri Guru Granth Sahib says: "Do not say that the Vedas, the Bible and the Koran are false. Those who do not contemplate them are false." Guru Granth Sahib page 1350; later stating "The seconds, minutes, and hours, days, weeks and months, and the various seasons originate from the one Sun; O nanak, in just the same way, the many forms originate from the Creator." Guru Granth Sahib page 12,13.

Catholicism

The Catholic Church, especially under John Paul II and Pope Benedict XVI, has identified relativism as one of the most significant problems for faith and morals today.

According to the Church and to some theologians, relativism, as a denial of absolute truth, leads to moral license and a denial of the possibility of sin and of God. Whether moral or epistemological, relativism constitutes a denial of the capacity of the human mind and reason to arrive at truth. Truth, according to Catholic theologians and philosophers (following Aristotle) consists of adequatio rei et intellectus, the correspondence of the mind and reality. Another way of putting it states that the mind has the same form as reality. This means when the form of the computer in front of someone (the type, color, shape, capacity, etc.) is also the form that is in their mind, then what they know is true because their mind corresponds to objective reality.

The denial of an absolute reference, of an axis mundi, denies God, who equates to Absolute Truth, according to these Christian theologians. They link relativism to secularism, an obstruction of religion in human life.

Leo XIII

Pope Leo XIII (1810–1903) was the first known Pope to use the word relativism in the encyclical Humanum genus (1884). Leo XIII condemned Freemasonry and claimed that its philosophical and political system was largely based on relativism.

John Paul II

John Paul II in Veritatis Splendor

As is immediately evident, the crisis of truth is not unconnected with this development. Once the idea of a universal truth about the good, knowable by human reason, is lost, inevitably the notion of conscience also changes. Conscience is no longer considered in its primordial reality as an act of a person's intelligence, the function of which is to apply the universal knowledge of the good in a specific situation and thus to express a judgment about the right conduct to be chosen here and now. Instead, there is a tendency to grant to the individual conscience the prerogative of independently determining the criteria of good and evil and then acting accordingly. Such an outlook is quite congenial to an individualist ethic, wherein each individual is faced with his own truth, different from the truth of others. Taken to its extreme consequences, this individualism leads to a denial of the very idea of human nature.

In Evangelium Vitae (The Gospel of Life), he says:

Freedom negates and destroys itself, and becomes a factor leading to the destruction of others, when it no longer recognizes and respects its essential link with the truth. When freedom, out of a desire to emancipate itself from all forms of tradition and authority, shuts out even the most obvious evidence of an objective and universal truth, which is the foundation of personal and social life, then the person ends up by no longer taking as the sole and indisputable point of reference for his own choices the truth about good and evil, but only his subjective and changeable opinion or, indeed, his selfish interest and whim.
Benedict XVI

In April 2005, in his homily during Mass prior to the conclave which would elect him as Pope, then Cardinal Joseph Ratzinger talked about the world "moving towards a dictatorship of relativism":

How many winds of doctrine we have known in recent decades, how many ideological currents, how many ways of thinking. The small boat of thought of many Christians has often been tossed about by these waves – thrown from one extreme to the other: from Marxism to liberalism, even to libertinism; from collectivism to radical individualism; from atheism to a vague religious mysticism; from agnosticism to syncretism, and so forth. Every day new sects are created and what Saint Paul says about human trickery comes true, with cunning which tries to draw those into error (cf Ephesians 4, 14). Having a clear Faith, based on the Creed of the Church, is often labeled today as a fundamentalism. Whereas, relativism, which is letting oneself be tossed and "swept along by every wind of teaching", looks like the only attitude acceptable to today's standards. We are moving towards a dictatorship of relativism which does not recognize anything as certain and which has as its highest goal one's own ego and one's own desires. However, we have a different goal: the Son of God, true man. He is the measure of true humanism. Being an "Adult" means having a faith which does not follow the waves of today's fashions or the latest novelties. A faith which is deeply rooted in friendship with Christ is adult and mature. It is this friendship which opens us up to all that is good and gives us the knowledge to judge true from false, and deceit from truth.

On June 6, 2005, Pope Benedict XVI told educators:

Today, a particularly insidious obstacle to the task of education is the massive presence in our society and culture of that relativism which, recognizing nothing as definitive, leaves as the ultimate criterion only the self with its desires. And under the semblance of freedom it becomes a prison for each one, for it separates people from one another, locking each person into his or her own 'ego'.

Then during the World Youth Day in August 2005, he also traced to relativism the problems produced by the communist and sexual revolutions, and provided a counter-counter argument.

In the last century we experienced revolutions with a common programme–expecting nothing more from God, they assumed total responsibility for the cause of the world in order to change it. And this, as we saw, meant that a human and partial point of view was always taken as an absolute guiding principle. Absolutizing what is not absolute but relative is called totalitarianism. It does not liberate man, but takes away his dignity and enslaves him. It is not ideologies that save the world, but only a return to the living God, our Creator, the Guarantor of our freedom, the Guarantor of what is really good and true.

Münchhausen trilemma

From Wikipedia, the free encyclopedia
 
Baron Munchausen pulls himself out of a mire by his own hair.

In epistemology, the Münchhausen trilemma is a thought experiment used to demonstrate the impossibility of proving any truth, even in the fields of logic and mathematics. If it is asked how any given proposition is known to be true, proof may be provided. Yet that same question can be asked of the proof, and any subsequent proof. The Münchhausen trilemma is that there are only three ways of completing a proof:

The trilemma, then, is the decision among the three equally unsatisfying options.

The name Münchhausen-Trilemma was coined by the German philosopher Hans Albert in 1968 in reference to a trilemma of "dogmatism versus infinite regress versus psychologism" used by Karl Popper. It is a reference to the problem of "bootstrapping", based on the story of Baron Munchausen (in German, "Münchhausen") pulling himself and the horse on which he was sitting out of a mire by his own hair. Like Munchausen, who cannot make progress because he has no solid ground to stand on, any purported justification of all knowledge must fail, because it must start from a position of no knowledge, and therefore cannot make progress. It must either start with some knowledge, as with dogmatism, not start at all, as with infinite regress, or be a circular argument, justified only by itself and have no solid foundation, much like Munchausen is only pulling on himself rather than some external handhold.

It is also known as Agrippa's trilemma or the Agrippan trilemma after a similar argument reported by Sextus Empiricus, which was attributed to Agrippa the Skeptic by Diogenes Laërtius. Sextus' argument, however, consists of five (not three) "modes". Popper in his original 1935 publication mentions neither Sextus nor Agrippa, but instead attributes his trilemma to German philosopher Jakob Friedrich Fries, leading some to call it Fries's trilemma as a result.

In contemporary epistemology, advocates of coherentism are supposed to accept the "circular" horn of the trilemma; foundationalists rely on the axiomatic argument. The view that accepts infinite regress is called infinitism.

Agrippa and the Pyrrhonists

The following tropes or "modes" for Pyrrhonism are given by Sextus Empiricus, in his Outlines of Pyrrhonism. According to Sextus, they are attributed "to the more recent Pyrrhonists" and by Diogenes Laërtius attributed to Agrippa the Skeptic. The tropes are:

  • Dissent – The uncertainty demonstrated by the differences of opinions among philosophers and people in general.
  • Progress ad infinitum – All proof rests on matters themselves in need of proof, and so on to infinity. https://en.wikipedia.org/wiki/M%C3%BCnchhausen_trilemma?
  • Relation – All things are changed as their relations become changed, or, as they are looked upon from different points of view.
  • Assumption – The truth asserted is based on an unsupported assumption.
  • Circularity – the truth asserted involves a circularity of proofs (known in scholasticism as "diallelus")

According to the mode deriving from dispute, we find that undecidable dissension about the matter proposed has come about both in ordinary life and among philosophers. Because of this we are not able to choose or to rule out anything, and we end up with suspension of judgement. In the mode deriving from infinite regress, we say that what is brought forward as a source of conviction for the matter proposed itself needs another such source, which itself needs another, and so ad infinitum, so that we have no point from which to begin to establish anything, and suspension of judgement follows. In the mode deriving from relativity, as we said above, the existing object appears to be such-and-such relative to the subject judging and to the things observed together with it, but we suspend judgement on what it is like in its nature. We have the mode from hypothesis when the Dogmatists, being thrown back ad infinitum, begin from something which they do not establish but claim to assume simply and without proof in virtue of a concession. The reciprocal mode occurs when what ought to be confirmatory of the object under investigation needs to be made convincing by the object under investigation; then, being unable to take either in order to establish the other, we suspend judgement about both.

With reference to these five tropes, the first and third are a short summary of the ten modes of Aenesidemus which were the basis of earlier Pyrrhonism. The three additional ones show a progress in the Pyrrhonist system, and a transition from the common objections derived from the fallibility of sense and opinion, to more abstract and metaphysical grounds of skepticism.

According to Victor Brochard, "the five tropes can be regarded as the most radical and most precise formulation of skepticism that has ever been given. In a sense, they are still irresistible today."

Fries's trilemma

Jakob Friedrich Fries formulated a similar trilemma in which statements can be accepted either:

The first two possibilities are rejected by Fries as unsatisfactory, requiring his adopting the third option. Karl Popper argued that a way to avoid the trilemma was to use an intermediate approach incorporating some dogmatism, some infinite regress, and some perceptual experience.

Albert's formulation

The argument proposed by Hans Albert runs as follows: All of the only three possible attempts to get a certain justification must fail:

  • All justifications in pursuit of "certain" knowledge have also to justify the means of their justification and doing so they have to justify anew the means of their justification. Therefore, there can be no end, only the hopeless situation of infinite regression
  • A circular argument can be used to justify by its mock impression of validity and soundness, but this sacrifices its usefulness (as the conclusion and premise are one and the same, no advancement in knowledge has taken place).
  • One can stop at self-evidence or common sense or fundamental principles or speaking ex cathedra or at any other evidence, but in doing so, the intention to install 'certain' justification is abandoned.

An English translation of a quote from the original German text by Albert is as follows:

Here, one has a mere choice between:

  1. An infinite regression, which appears because of the necessity to go ever further back, but is not practically feasible and does not, therefore, provide a certain foundation.
  2. A logical circle in the deduction, which is caused by the fact that one, in the need to found, falls back on statements which had already appeared before as requiring a foundation, and which circle does not lead to any certain foundation either.
  3. A break of searching at a certain point, which indeed appears principally feasible, but would mean a random suspension of the principle of sufficient reason.

Albert stressed repeatedly that there is no limitation of the Münchhausen trilemma to deductive conclusions. The verdict concerns also inductive, causal, transcendental, and all otherwise structured justifications. They all will be in vain.

Therefore, certain justification is impossible to attain. Once having given up the classical idea of certain knowledge, one can stop the process of justification where one wants to stop, presupposed one is ready to start critical thinking at this point always anew if necessary.

This trilemma rounds off the classical problem of justification in the theory of knowledge.

The failure of proving exactly any truth as expressed by the Münchhausen trilemma does not have to lead to dismissal of objectivity, as with relativism. One example of an alternative is the fallibilism of Karl Popper and Hans Albert, accepting that certainty is impossible, but that it is best to get as close as possible to truth, while remembering our uncertainty.

In Albert's view, the impossibility to prove any certain truth is not in itself a certain truth. After all, one needs to assume some basic rules of logical inference to derive his result, and in doing so must either abandon the pursuit of "certain" justification, as above, or attempt to justify these rules, etc. He suggests that it has to be taken as true as long as nobody has come forward with a truth which is scrupulously justified as a certain truth. Several philosophers defied Albert's challenge; his responses to such criticisms can be found in his long addendum to his Treatise on Critical Reason and later articles.

Circulatory system

From Wikipedia, the free encyclopedia

Circulatory system
Circulatory System en.svg
The human circulatory system (simplified). Red indicates oxygenated blood carried in arteries. Blue indicates deoxygenated blood carried in veins. Capillaries, which join the arteries and veins, and the lymphatic vessels are not shown.
 
Identifiers
MeSHD002319
TA98A12.0.00.000
TA23891
FMA7161

The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that permits blood to circulate and transport nutrients (such as amino acids and electrolytes), oxygen, carbon dioxide, hormones, and blood cells to and from the cells in the body to provide nourishment and help in fighting diseases, stabilize temperature and pH, and maintain homeostasis.

The circulatory system includes the lymphatic system, which circulates lymph. The passage of lymph takes much longer than that of blood. Blood is a fluid consisting of plasma, red blood cells, white blood cells, and platelets that is circulated by the heart through the vertebrate vascular system, carrying oxygen and nutrients to and waste materials away from all body tissues. Lymph is essentially recycled excess blood plasma after it has been filtered from the interstitial fluid (between cells) and returned to the lymphatic system. The cardiovascular (from Latin words meaning "heart" and "vessel") system comprises the blood, heart, and blood vessels. The lymph, lymph nodes, and lymph vessels form the lymphatic system, which returns filtered blood plasma from the interstitial fluid (between cells) as lymph.

The circulatory system of the blood has two components, a systemic circulation and a pulmonary circulation. While humans and other vertebrates have a closed cardiovascular system (which means that the blood never leaves the network of arteries, veins and capillaries), some invertebrate groups have an open cardiovascular system. The lymphatic system, in contrast, is an open system providing an accessory route for excess interstitial fluid to be returned to the blood. The more primitive, diploblastic animal phyla lack circulatory systems.

Many diseases affect the circulatory system. This includes cardiovascular disease, affecting the cardiovascular system, and lymphatic disease affecting the lymphatic system. Cardiologists are medical professionals which specialise in the heart, and cardiothoracic surgeons specialise in operating on the heart and its surrounding areas. Vascular surgeons focus on other parts of the circulatory system.

Structure

Cardiovascular system

Depiction of the heart, major veins and arteries constructed from body scans
 
Cross section of a human artery

The essential components of the human cardiovascular system are the heart, blood and blood vessels. It includes the pulmonary circulation, a "loop" through the lungs where blood is oxygenated; and the systemic circulation, a "loop" through the rest of the body to provide oxygenated blood. The systemic circulation can also be seen to function in two parts – a macrocirculation and a microcirculation. An average adult contains five to six quarts (roughly 4.7 to 5.7 liters) of blood, accounting for approximately 7% of their total body weight. Blood consists of plasma, red blood cells, white blood cells, and platelets. Also, the digestive system works with the circulatory system to provide the nutrients the system needs to keep the heart pumping.

The cardiovascular systems of humans are closed, meaning that the blood never leaves the network of blood vessels. In contrast, oxygen and nutrients diffuse across the blood vessel layers and enter interstitial fluid, which carries oxygen and nutrients to the target cells, and carbon dioxide and wastes in the opposite direction. The other component of the circulatory system, the lymphatic system, is open.

Arteries

Oxygenated blood enters the systemic circulation when leaving the left ventricle, through the aortic semilunar valve. The first part of the systemic circulation is the aorta, a massive and thick-walled artery. The aorta arches and gives branches supplying the upper part of the body after passing through the aortic opening of the diaphragm at the level of thoracic ten vertebra, it enters the abdomen. Later it descends down and supplies branches to abdomen, pelvis, perineum and the lower limbs. The walls of aorta are elastic. This elasticity helps to maintain the blood pressure throughout the body. When the aorta receives almost five litres of blood from the heart, it recoils and is responsible for pulsating blood pressure. Moreover, as aorta branches into smaller arteries, their elasticity goes on decreasing and their compliance goes on increasing.

Capillaries

Arteries branch into small passages called arterioles and then into the capillaries. The capillaries merge to bring blood into the venous system.

Veins

Capillaries merge into venules, which merge into veins. The venous system feeds into the two major veins: the superior vena cava – which mainly drains tissues above the heart – and the inferior vena cava – which mainly drains tissues below the heart. These two large veins empty into the right atrium of the heart.

Portal veins

The general rule is that arteries from the heart branch out into capillaries, which collect into veins leading back to the heart. Portal veins are a slight exception to this. In humans the only significant example is the hepatic portal vein which combines from capillaries around the gastrointestinal tract where the blood absorbs the various products of digestion; rather than leading directly back to the heart, the hepatic portal vein branches into a second capillary system in the liver.

Heart

View from the front

The heart pumps oxygenated blood to the body and deoxygenated blood to the lungs. In the human heart there is one atrium and one ventricle for each circulation, and with both a systemic and a pulmonary circulation there are four chambers in total: left atrium, left ventricle, right atrium and right ventricle. The right atrium is the upper chamber of the right side of the heart. The blood that is returned to the right atrium is deoxygenated (poor in oxygen) and passed into the right ventricle to be pumped through the pulmonary artery to the lungs for re-oxygenation and removal of carbon dioxide. The left atrium receives newly oxygenated blood from the lungs as well as the pulmonary vein which is passed into the strong left ventricle to be pumped through the aorta to the different organs of the body.

Coronary vessels

The heart itself is supplied with oxygen and nutrients through a small "loop" of the systemic circulation and derives very little from the blood contained within the four chambers. The coronary circulation system provides a blood supply to the heart muscle itself. The coronary circulation begins near the origin of the aorta by two coronary arteries: the right coronary artery and the left coronary artery. After nourishing the heart muscle, blood returns through the coronary veins into the coronary sinus and from this one into the right atrium. Back flow of blood through its opening during atrial systole is prevented by Thebesian valve. The smallest cardiac veins drain directly into the heart chambers.

Lungs

The pulmonary circulation as it passes from the heart. Showing both the pulmonary and bronchial arteries.

The circulatory system of the lungs is the portion of the cardiovascular system in which oxygen-depleted blood is pumped away from the heart, via the pulmonary artery, to the lungs and returned, oxygenated, to the heart via the pulmonary vein.

Oxygen-deprived blood from the superior and inferior vena cava enters the right atrium of the heart and flows through the tricuspid valve (right atrioventricular valve) into the right ventricle, from which it is then pumped through the pulmonary semilunar valve into the pulmonary artery to the lungs. Gas exchange occurs in the lungs, whereby CO
2
is released from the blood, and oxygen is absorbed. The pulmonary vein returns the now oxygen-rich blood to the left atrium.

A separate system known as the bronchial circulation supplies blood to the tissue of the larger airways of the lung.

Systemic circulation

The systemic circulation and capillary networks shown and also as separate from the pulmonary circulation

Systemic circulation is the portion of the cardiovascular system which transports oxygenated blood away from the heart through the aorta from the left ventricle where the blood has been previously deposited from pulmonary circulation, to the rest of the body, and returns oxygen-depleted blood back to the heart.

Brain

The brain has a dual blood supply that comes from arteries at its front and back. These are called the "anterior" and "posterior" circulation respectively. The anterior circulation arises from the internal carotid arteries and supplies the front of the brain. The posterior circulation arises from the vertebral arteries, and supplies the back of the brain and brainstem. The circulation from the front and the back join together (anastomise) at the Circle of Willis.

Kidneys

The renal circulation receives around 20% of the cardiac output. It branches from the abdominal aorta and returns blood to the ascending vena cava. It is the blood supply to the kidneys, and contains many specialized blood vessels.

Lymphatic system

The lymphatic system is part of the circulatory system in many complex animals such as mammals and birds. It is a network of lymphatic vessels and lymph capillaries, lymph nodes and organs, and lymphatic tissues and circulating lymph. One of its major functions is to carry the lymph, draining and returning interstitial fluid back towards the heart for return to the cardiovascular system, by emptying into the lymphatic ducts. Its other main function is in the adaptive immune system.

Development

The development of the circulatory system starts with vasculogenesis in the embryo. The human arterial and venous systems develop from different areas in the embryo. The arterial system develops mainly from the aortic arches, six pairs of arches that develop on the upper part of the embryo. The venous system arises from three bilateral veins during weeks 4 – 8 of embryogenesis. Fetal circulation begins within the 8th week of development. Fetal circulation does not include the lungs, which are bypassed via the truncus arteriosus. Before birth the fetus obtains oxygen (and nutrients) from the mother through the placenta and the umbilical cord.

Heart

Arteries

Animation of a typical human red blood cell cycle in the circulatory system. This animation occurs at a faster rate (~20 seconds of the average 60-second cycle) and shows the red blood cell deforming as it enters capillaries, as well as the bars changing color as the cell alternates in states of oxygenation along the circulatory system.

The human arterial system originates from the aortic arches and from the dorsal aortae starting from week 4 of embryonic life. The first and second aortic arches regress and form only the maxillary arteries and stapedial arteries respectively. The arterial system itself arises from aortic arches 3, 4 and 6 (aortic arch 5 completely regresses).

The dorsal aortae, present on the dorsal side of the embryo, are initially present on both sides of the embryo. They later fuse to form the basis for the aorta itself. Approximately thirty smaller arteries branch from this at the back and sides. These branches form the intercostal arteries, arteries of the arms and legs, lumbar arteries and the lateral sacral arteries. Branches to the sides of the aorta will form the definitive renal, suprarenal and gonadal arteries. Finally, branches at the front of the aorta consist of the vitelline arteries and umbilical arteries. The vitelline arteries form the celiac, superior and inferior mesenteric arteries of the gastrointestinal tract. After birth, the umbilical arteries will form the internal iliac arteries.

Veins

The human venous system develops mainly from the vitelline veins, the umbilical veins and the cardinal veins, all of which empty into the sinus venosus.

Function

Cardiovascular system

About 98.5% of the oxygen in a sample of arterial blood in a healthy human, breathing air at sea-level pressure, is chemically combined with hemoglobin molecules. About 1.5% is physically dissolved in the other blood liquids and not connected to hemoglobin. The hemoglobin molecule is the primary transporter of oxygen in mammals and many other species.

Lymphatic system

Clinical significance

Many diseases affect the circulatory system. These include a number of cardiovascular diseases, affecting the cardiovascular system, and lymphatic diseases affecting the lymphatic system. Cardiologists are medical professionals which specialise in the heart, and cardiothoracic surgeons specialise in operating on the heart and its surrounding areas. Vascular surgeons focus on other parts of the circulatory system.

Cardiovascular disease

Diseases affecting the cardiovascular system are called cardiovascular disease.

Many of these diseases are called "lifestyle diseases" because they develop over time and are related to a person's exercise habits, diet, whether they smoke, and other lifestyle choices a person makes. Atherosclerosis is the precursor to many of these diseases. It is where small atheromatous plaques build up in the walls of medium and large arteries. This may eventually grow or rupture to occlude the arteries. It is also a risk factor for acute coronary syndromes, which are diseases that are characterised by a sudden deficit of oxygenated blood to the heart tissue. Atherosclerosis is also associated with problems such as aneurysm formation or splitting ("dissection") of arteries.

Another major cardiovascular disease involves the creation of a clot, called a "thrombus". These can originate in veins or arteries. Deep venous thrombosis, which mostly occurs in the legs, is one cause of clots in the veins of the legs, particularly when a person has been stationary for a long time. These clots may embolise, meaning travel to another location in the body. The results of this may include pulmonary embolus, transient ischaemic attacks, or stroke.

Cardiovascular diseases may also be congenital in nature, such as heart defects or persistent fetal circulation, where the circulatory changes that are supposed to happen after birth do not. Not all congenital changes to the circulatory system are associated with diseases, a large number are anatomical variations.

Investigations

The function and health of the circulatory system and its parts are measured in a variety of manual and automated ways. These include simple methods such as those that are part of the cardiovascular examination, including the taking of a person's pulse as an indicator of a person's heart rate, the taking of blood pressure through a sphygmomanometer or the use of a stethoscope to listen to the heart for murmurs which may indicate problems with the heart's valves. An electrocardiogram can also be used to evaluate the way in which electricity is conducted through the heart.

Other more invasive means can also be used. A cannula or catheter inserted into an artery may be used to measure pulse pressure or pulmonary wedge pressures. Angiography, which involves injecting a dye into an artery to visualise an arterial tree, can be used in the heart (coronary angiography) or brain. At the same time as the arteries are visualised, blockages or narrowings may be fixed through the insertion of stents, and active bleeds may be managed by the insertion of coils. An MRI may be used to image arteries, called an MRI angiogram. For evaluation of the blood supply to the lungs a CT pulmonary angiogram may be used.

Vascular ultrasonography include for example:

Surgery

There are a number of surgical procedures performed on the circulatory system:

Cardiovascular procedures are more likely to be performed in an inpatient setting than in an ambulatory care setting; in the United States, only 28% of cardiovascular surgeries were performed in the ambulatory care setting.[13]

Society and culture

In Ancient Greece, the heart was thought to be the source of innate heat for the body. The circulatory system as we know it was discovered by William Harvey.

Other animals

The open circulatory system of the grasshopper – made up of a heart, vessels and hemolymph. The hemolymph is pumped through the heart, into the aorta, dispersed into the head and throughout the hemocoel, then back through the ostia in the heart and the process repeated.

While humans, as well as other vertebrates, have a closed blood circulatory system (meaning that the blood never leaves the network of arteries, veins and capillaries), some invertebrate groups have an open circulatory system containing a heart but limited blood vessels. The most primitive, diploblastic animal phyla lack circulatory systems.

An additional transport system, the lymphatic system, which is only found in animals with a closed blood circulation, is an open system providing an accessory route for excess interstitial fluid to be returned to the blood.

The blood vascular system first appeared probably in an ancestor of the triploblasts over 600 million years ago, overcoming the time-distance constraints of diffusion, while endothelium evolved in an ancestral vertebrate some 540–510 million years ago.

Open circulatory system

In arthropods, the open circulatory system is a system in which a fluid in a cavity called the hemocoel bathes the organs directly with oxygen and nutrients, with there being no distinction between blood and interstitial fluid; this combined fluid is called hemolymph or haemolymph. Muscular movements by the animal during locomotion can facilitate hemolymph movement, but diverting flow from one area to another is limited. When the heart relaxes, blood is drawn back toward the heart through open-ended pores (ostia).

Hemolymph fills all of the interior hemocoel of the body and surrounds all cells. Hemolymph is composed of water, inorganic salts (mostly sodium, chloride, potassium, magnesium, and calcium), and organic compounds (mostly carbohydrates, proteins, and lipids). The primary oxygen transporter molecule is hemocyanin.

There are free-floating cells, the hemocytes, within the hemolymph. They play a role in the arthropod immune system.

Flatworms, such as this Pseudoceros bifurcus, lack specialized circulatory organs.

Closed circulatory system

Two-chambered heart of a fish

The circulatory systems of all vertebrates, as well as of annelids (for example, earthworms) and cephalopods (squids, octopuses and relatives) always keep their circulating blood enclosed within heart chambers or blood vessels and are classified as closed, just as in humans. Still, the systems of fish, amphibians, reptiles, and birds show various stages of the evolution of the circulatory system. Closed systems permit blood to be directed to the organs that require it.

In fish, the system has only one circuit, with the blood being pumped through the capillaries of the gills and on to the capillaries of the body tissues. This is known as single cycle circulation. The heart of fish is, therefore, only a single pump (consisting of two chambers).

In amphibians and most reptiles, a double circulatory system is used, but the heart is not always completely separated into two pumps. Amphibians have a three-chambered heart.

In reptiles, the ventricular septum of the heart is incomplete and the pulmonary artery is equipped with a sphincter muscle. This allows a second possible route of blood flow. Instead of blood flowing through the pulmonary artery to the lungs, the sphincter may be contracted to divert this blood flow through the incomplete ventricular septum into the left ventricle and out through the aorta. This means the blood flows from the capillaries to the heart and back to the capillaries instead of to the lungs. This process is useful to ectothermic (cold-blooded) animals in the regulation of their body temperature.

Birds, mammals, and crocodilians show complete separation of the heart into two pumps, for a total of four heart chambers; it is thought that the four-chambered heart of birds and crocodilians evolved independently from that of mammals. Double circulatory systems permit blood to be repressurized after returning from the lungs, speeding up delivery of oxygen to tissues.

No circulatory system

Circulatory systems are absent in some animals, including flatworms. Their body cavity has no lining or enclosed fluid. Instead, a muscular pharynx leads to an extensively branched digestive system that facilitates direct diffusion of nutrients to all cells. The flatworm's dorso-ventrally flattened body shape also restricts the distance of any cell from the digestive system or the exterior of the organism. Oxygen can diffuse from the surrounding water into the cells, and carbon dioxide can diffuse out. Consequently, every cell is able to obtain nutrients, water and oxygen without the need of a transport system.

Some animals, such as jellyfish, have more extensive branching from their gastrovascular cavity (which functions as both a place of digestion and a form of circulation), this branching allows for bodily fluids to reach the outer layers, since the digestion begins in the inner layers.

History

Human anatomical chart of blood vessels, with heart, lungs, liver and kidneys included. Other organs are numbered and arranged around it. Before cutting out the figures on this page, Vesalius suggests that readers glue the page onto parchment and gives instructions on how to assemble the pieces and paste the multilayered figure onto a base "muscle man" illustration. "Epitome", fol.14a. HMD Collection, WZ 240 V575dhZ 1543.

The earliest known writings on the circulatory system are found in the Ebers Papyrus (16th century BCE), an ancient Egyptian medical papyrus containing over 700 prescriptions and remedies, both physical and spiritual. In the papyrus, it acknowledges the connection of the heart to the arteries. The Egyptians thought air came in through the mouth and into the lungs and heart. From the heart, the air travelled to every member through the arteries. Although this concept of the circulatory system is only partially correct, it represents one of the earliest accounts of scientific thought.

In the 6th century BCE, the knowledge of circulation of vital fluids through the body was known to the Ayurvedic physician Sushruta in ancient India. He also seems to have possessed knowledge of the arteries, described as 'channels' by Dwivedi & Dwivedi (2007). The valves of the heart were discovered by a physician of the Hippocratean school around the 4th century BCE. However, their function was not properly understood then. Because blood pools in the veins after death, arteries look empty. Ancient anatomists assumed they were filled with air and that they were for the transport of air.

The Greek physician, Herophilus, distinguished veins from arteries but thought that the pulse was a property of arteries themselves. Greek anatomist Erasistratus observed that arteries that were cut during life bleed. He ascribed the fact to the phenomenon that air escaping from an artery is replaced with blood that entered by very small vessels between veins and arteries. Thus he apparently postulated capillaries but with reversed flow of blood.

In 2nd-century AD Rome, the Greek physician Galen knew that blood vessels carried blood and identified venous (dark red) and arterial (brighter and thinner) blood, each with distinct and separate functions. Growth and energy were derived from venous blood created in the liver from chyle, while arterial blood gave vitality by containing pneuma (air) and originated in the heart. Blood flowed from both creating organs to all parts of the body where it was consumed and there was no return of blood to the heart or liver. The heart did not pump blood around, the heart's motion sucked blood in during diastole and the blood moved by the pulsation of the arteries themselves.

Galen believed that the arterial blood was created by venous blood passing from the left ventricle to the right by passing through 'pores' in the interventricular septum, air passed from the lungs via the pulmonary artery to the left side of the heart. As the arterial blood was created 'sooty' vapors were created and passed to the lungs also via the pulmonary artery to be exhaled.

In 1025, The Canon of Medicine by the Persian physician, Avicenna, "erroneously accepted the Greek notion regarding the existence of a hole in the ventricular septum by which the blood traveled between the ventricles." Despite this, Avicenna "correctly wrote on the cardiac cycles and valvular function", and "had a vision of blood circulation" in his Treatise on Pulse. While also refining Galen's erroneous theory of the pulse, Avicenna provided the first correct explanation of pulsation: "Every beat of the pulse comprises two movements and two pauses. Thus, expansion : pause : contraction : pause. [...] The pulse is a movement in the heart and arteries ... which takes the form of alternate expansion and contraction."

In 1242, the Arabian physician, Ibn al-Nafis, became the first person to accurately describe the process of pulmonary circulation, for which he is sometimes considered the father of circulatory physiology. Ibn al-Nafis stated in his Commentary on Anatomy in Avicenna's Canon:

"...the blood from the right chamber of the heart must arrive at the left chamber but there is no direct pathway between them. The thick septum of the heart is not perforated and does not have visible pores as some people thought or invisible pores as Galen thought. The blood from the right chamber must flow through the vena arteriosa (pulmonary artery) to the lungs, spread through its substances, be mingled there with air, pass through the arteria venosa (pulmonary vein) to reach the left chamber of the heart and there form the vital spirit..."

In addition, Ibn al-Nafis had an insight into what would become a larger theory of the capillary circulation. He stated that "there must be small communications or pores (manafidh in Arabic) between the pulmonary artery and vein," a prediction that preceded the discovery of the capillary system by more than 400 years. Ibn al-Nafis' theory, however, was confined to blood transit in the lungs and did not extend to the entire body.

Michael Servetus was the first European to describe the function of pulmonary circulation, although his achievement was not widely recognized at the time, for a few reasons. He firstly described it in the "Manuscript of Paris" (near 1546), but this work was never published. And later he published this description, but in a theological treatise, Christianismi Restitutio, not in a book on medicine. Only three copies of the book survived but these remained hidden for decades, the rest were burned shortly after its publication in 1553 because of persecution of Servetus by religious authorities.

Better known discovery of pulmonary circulation was by Vesalius's successor at Padua, Realdo Colombo, in 1559.

Finally, the English physician William Harvey, a pupil of Hieronymus Fabricius (who had earlier described the valves of the veins without recognizing their function), performed a sequence of experiments and published his Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus in 1628, which "demonstrated that there had to be a direct connection between the venous and arterial systems throughout the body, and not just the lungs. Most importantly, he argued that the beat of the heart produced a continuous circulation of blood through minute connections at the extremities of the body. This is a conceptual leap that was quite different from Ibn al-Nafis' refinement of the anatomy and bloodflow in the heart and lungs." This work, with its essentially correct exposition, slowly convinced the medical world. However, Harvey was not able to identify the capillary system connecting arteries and veins; these were later discovered by Marcello Malpighi in 1661.

In 1956, André Frédéric Cournand, Werner Forssmann and Dickinson W. Richards were awarded the Nobel Prize in Medicine "for their discoveries concerning heart catheterization and pathological changes in the circulatory system." In his Nobel lecture, Forssmann credits Harvey as birthing cardiology with the publication of his book in 1628.

In the 1970s, Diana McSherry developed computer-based systems to create images of the circulatory system and heart without the need for surgery.

Wealth inequality in the United States

From Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Wealth_inequality_in_the_United_States ...