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Antirealism
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In analytic philosophy, the term antirealism describes any position involving either the denial of an objective reality or the denial that verificationtranscendent statements are either true or false. This latter construal is sometimes expressed by saying "there is no fact of the matter as to whether or not P". Thus, one may speak of antirealism with respect to other minds, the past, the future, universals, mathematical entities (such as natural numbers), moral categories, the material world, or even thought. The two construals are clearly distinct but often confused. For example, an "antirealist" who denies that other minds exist (i. e., a solipsist) is quite different from an "antirealist" who claims that there is no fact of the matter as to whether or not there are unobservable other minds (i. e., a logical behaviorist).
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Antirealism in philosophy
Michael Dummett
The term was coined by Michael Dummett, who introduced it in his paper Realism to reexamine a number of classical philosophical disputes involving such doctrines as nominalism, conceptual realism, idealism and phenomenalism. The novelty of Dummett's approach consisted in seeing these disputes as analogous to the dispute between intuitionism and Platonism in the philosophy of mathematics.
According to intuitionists (antirealists with respect to mathematical objects), the truth of a mathematical statement consists in our ability to prove it. According to platonists (realists), the truth of a statement consists in its correspondence to objective reality. Thus, intuitionists are ready to accept a statement of the form "P or Q" as true only if we can prove P or if we can prove Q: this is called the disjunction property. In particular, we cannot in general claim that "P or not P" is true (the law of Excluded Middle), since in some cases we may not be able to prove the statement "P" nor prove the statement "not P".^{[citation needed]} Similarly, intuitionists object to the existence property for classical logic, where one can prove <math>\exists x.\phi(x)</math>, without being able to produce any term <math>t</math> of which <math>\phi</math> holds.
Dummett argues that the intuitionistic notion of truth lies at the bottom of various classical forms of antirealism. He uses this notion to reinterpret phenomenalism, claiming that it need not take the form of a reductionism (often considered untenable).
Dummett's writings on antirealism also draw heavily on the later writings of Wittgenstein concerning meaning and rule following. In fact, Dummett's writings on antirealism can be seen as an attempt to integrate central ideas from the Philosophical Investigations into analytical philosophy.
Antirealism in the sense that Dummett uses the term is also often called semantic antirealism.
Hilary Putnam's "internal realism"
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Despite being at one time a defender of metaphysical realism, Hilary Putnam later abandoned this view in favor of a position he termed "internal realism".
Precursors
Doubts about the possibility of definite truth have been expressed since ancient times, for instance in the skepticism of Pyrrho. Antirealism about matter or physical entities also has a long history. It can be found in the idealism of Berkeley, as well as Hegel and other postKantians.
Metaphysical realism visàvis internal realism
Antirealist arguments
Idealists are skeptics about the physical world, maintaining either: 1) that nothing exists outside the mind, or 2) that we would have no access to a mindindependent reality even if it may exist; the latter case often takes the form of a denial of the idea that we can have unconceptualised experiences (see Myth of the Given). Conversely, most realists (specifically, indirect realists) hold that perceptions or sense data are caused by mindindependent objects. But this introduces the possibility of another kind of skepticism: since our understanding of causality is that the same effect can be produced by multiple causes, there is a lack of determinacy about what one is really perceiving. A concrete example of a situation where an individual's sensory input might be caused by something other than what he thinks is causing it is the brain in a vat scenario.
On a more abstract level, model theoretic arguments hold that a given set of symbols in a theory can be mapped onto any number of sets of realworld objects — each set being a "model" of the theory — providing the interrelationships between the objects are the same. (Compare with symbol grounding.)
Antirealism in science
In philosophy of science, antirealism applies chiefly to claims about the nonreality of "unobservable" entities such as electrons or genes, which are not detectable with human senses. For a brief discussion comparing such antirealism to its opposite, realism, see (Okasha 2002, ch. 4). Ian Hacking (1999, p. 84) also uses the same definition. One prominent position in the philosophy of science is instrumentalism, which is a nonrealist position. Nonrealism takes a purely agnostic view towards the existence of unobservable entities: unobservable entity X serves simply as an instrument to aid in the success of theory Y. We need not determine the existence or nonexistence of X. Some scientific antirealists argue further, however, and deny that unobservables exist even as nontruth conditioned instruments.
Antirealism in mathematics
Realism in the philosophy of mathematics is the claim that mathematical entities such as number have a mindindependent existence. The main forms are empiricism, which associates numbers with concrete physical objects; and Platonism, according to which numbers are abstract, nonphysical entities.
The "epistemic argument" against Platonism has been made by Paul Benacerraf and Hartry Field. Platonism posits that mathematical objects are abstract entities. By general agreement, abstract entities cannot interact causally with concrete, physical entities. ("the truthvalues of our mathematical assertions depend on facts involving platonic entities that reside in a realm outside of spacetime"^{[1]}) Whilst our knowledge of concrete, physical objects is based on our ability to perceive them, and therefore to causally interact with them, there is no parallel account of how mathematicians come to have knowledge of abstract objects.^{[2]}^{[3]}^{[4]} ("An account of mathematical truth ..must be consistent with the possibility of mathematical knowledge"^{[5]}). Another way of making the point is that if the Platonic world were to disappear, it would make no difference to the ability of mathematicians to generate proofs, etc., which is already fully accountable in terms of physical processes in their brains.
Field developed his views into fictionalism. Benacerraf also developed the philosophy of mathematical structuralism, according to which there are no mathematical objects. Nonetheless, some versions of structuralism are compatible with some versions of realism.
The argument hinges on the idea that a satisfactory naturalistic account of thought processes in terms of brain processes can be given for mathematical reasoning along with everything else. One line of defense is to maintain that this is false, so that mathematical reasoning uses some special intuition that involves contact with the Platonic realm. A modern form of this argument is given by Sir Roger Penrose.^{[6]}
Another line of defense is to maintain that abstract objects are relevant to mathematical reasoning in a way that is non causal, and not analogous to perception. This argument is developed by Jerrold Katz in his book Realistic Rationalism.
A more radical defense is to deny the separation of physical world and the platonic world, i.e. the mathematical universe hypothesis. In that case, a mathematician's knowledge of mathematics is one mathematical object making contact with another.
See also
 Constructivist epistemology
 Crispin Wright
 Deflationary theory of truth
 Fact
 Idealism
 Intuitionistic logic
 Irrealism (philosophy)
 Münchhausen trilemma
 Neil Tennant (philosopher)
 Nihilism
 Philosophical realism
 Quasirealism
 Simulated reality
 Theory of Everything (ToE)
References
 ^ Field, Hartry, 1989, Realism, Mathematics, and Modality, Oxford: Blackwell, p. 68
 ^ "Since abstract objects are outside the nexus of causes and effects, and thus perceptually inaccessible, they cannot be known through their effects on us" Katz, J. Realistic Rationalism, p. 15
 ^ Philosophy Now: Mathematical_Knowledge_A_Dilemma Mathematical Knowledge: A dilemma
 ^ Stanford Encyclopeida of Philosophy
 ^ Benacceraf, 1973, p. 409
 ^ Review of The Emperor's New Mind >
Bibliography
 Christine Baron, Manfred Engel (eds.) (2010). Realism/AntiRealism in 20thCentury Literature. Rodopi: 2010. ISBN 9789042031159
 Lee Braver (2007). A Thing of This World: a History of Continental AntiRealism, Northwestern University Press: 2007.
 Michael Dummett (1963). Realism, reprinted in: Truth and Other Enigmas, Harvard University Press: 1978, pp. 145–165.
 Michael Dummett (1967). Platonism, reprinted in: Truth and Other Enigmas, Harvard University Press: 1978, pp. 202–214.
 Ian Hacking (1999). The Social Construction of What?. Harvard University Press: 2001.
 Samir Okasha (2002). Philosophy of Science: A Very Short Introduction. Oxford University Press.
External links
 Semantic challenges to realism in the Stanford Encyclopedia of Philosophy
