Metaphysical anti-realism One kind of
metaphysical anti-realism maintains a
skepticism about the physical world, arguing either: 1) that nothing exists outside the mind, or 2) that we would have no access to a mind-independent reality, even if it exists. 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 mind-independent 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, as in the
brain in a vat scenario. The main alternative to this sort of metaphysical anti-realism is
metaphysical realism. On a more abstract level,
model-theoretic anti-realist arguments hold that a given set of
symbols in a
theory can be mapped onto any number of sets of real-world objects—each set being a "model" of the theory—provided the relationship between the objects is the same (compare with
symbol grounding.) In
ancient Greek philosophy,
nominalist (anti-realist) doctrines about
universals were proposed by the
Stoics, especially
Chrysippus. In
early modern philosophy,
conceptualist anti-realist doctrines about universals were proposed by thinkers like
René Descartes,
John Locke,
Baruch Spinoza,
Gottfried Wilhelm Leibniz,
George Berkeley, and
David Hume. In
late modern philosophy, anti-realist doctrines about knowledge were proposed by the
German idealist Georg Wilhelm Friedrich Hegel. Hegel was a proponent of what is now called
inferentialism: he believed that the ground for the axioms and the foundation for the validity of the inferences are the right consequences and that the axioms do not explain the consequence. Kant and Hegel held conceptualist views about universals. In
contemporary philosophy, anti-realism was revived in the form of
empirio-criticism,
logical positivism,
semantic anti-realism and scientific
instrumentalism (see below).
Mathematical anti-realism In the
philosophy of mathematics, realism is the claim that mathematical entities such as 'number' have an observer-independent existence.
Empiricism, which associates numbers with concrete physical objects, and
Platonism, in which numbers are abstract, non-physical entities, are the preeminent forms of mathematical realism. 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 physical entities ("the truth-values of our mathematical assertions depend on facts involving platonic entities that reside in a realm outside of space-time"). Whilst our knowledge of 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. 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.
Counterarguments Anti-realist arguments hinge on the idea that a satisfactory,
naturalistic account of thought processes can be given for mathematical reasoning. 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, as in the argument given by
Sir Roger Penrose. 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 2000 book
Realistic Rationalism. In this book, he put forward a position called
realistic rationalism, which combines metaphysical realism and
rationalism. A more radical defense is to deny the separation of physical world and the platonic world, i.e. the
mathematical universe hypothesis (a variety of
mathematicism). In that case, a mathematician's knowledge of mathematics is one mathematical object making contact with another.
Semantic anti-realism The term "
anti-realism" was introduced by
Michael Dummett in his 1963 paper "Realism" in order to re-examine a number of classical philosophical disputes, involving such doctrines as
nominalism,
Platonic realism,
idealism and
phenomenalism. The novelty of Dummett's approach consisted in portraying these disputes as analogous to the dispute between
intuitionism and
Platonism in the
philosophy of mathematics. According to intuitionists (anti-realists with respect to mathematical objects), the
truth of a mathematical statement consists in our ability to prove it. According to Platonic realists, the truth of a statement is proven 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. 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". Similarly, intuitionists object to the
existence property for classical logic, where one can prove \exists x.\phi(x), without being able to produce any term t of which \phi holds. Dummett argues that this notion of truth lies at the bottom of various classical forms of anti-realism, and uses it to re-interpret
phenomenalism, claiming that it need not take the form of
reductionism. Dummett's writings on anti-realism draw heavily on the later writings of
Ludwig Wittgenstein, concerning meaning and rule following, and can be seen as an attempt to integrate central ideas from the
Philosophical Investigations into the constructive tradition of
analytic philosophy deriving from
Gottlob Frege.
Scientific anti-realism In
philosophy of science, anti-realism applies chiefly to claims about the non-reality of "unobservable" entities such as
electrons or
genes, which are not detectable with human senses. One prominent variety of
scientific anti-realism is
instrumentalism, which takes a purely agnostic view towards the existence of unobservable entities, in which the unobservable entity X serves as an instrument to aid in the success of theory Y and does not require proof for the existence or non-existence of X.
Anti-representationalism Anti-representationalism rejects the idea that thought and language function by mirroring or representing an independent reality. Instead, it adopts a
deflationary view of truth and reference, treating them as pragmatic tools within discourse rather than robust semantic relations. Anti-representationalists like
Richard Rorty and
Huw Price argue that all ontological commitments are framework-dependent, denying any privileged "external" perspective to judge which claims (including scientific ones) correspond to reality. •
The Semantic Thesis: Moral statements have meaning, they express propositions, or are the kind of things that can be true or false. •
The Alethic Thesis: Some moral propositions are true. •
The Metaphysical Thesis: The metaphysical status of moral facts is robust and ordinary, not importantly different from other facts about the world. Different version of moral anti-realism deny different statements: specifically,
non-cognitivism denies the first claim, arguing that moral statements have no meaning or truth content,
error theory denies the second claim, arguing that all moral statements are false, and
ethical subjectivism denies the third claim, arguing that the truth of moral statements is mind dependent. Examples of anti-realist moral theories might be: •
Ethical subjectivism •
Non-cognitivism •
Emotivism •
Prescriptivism •
Quasi-realism •
Projectivism •
Moral fictionalism •
Moral nihilism •
Moral skepticism There is a debate as to whether
moral relativism is actually an anti-realist position. While many versions deny the metaphysical thesis, some do not, as one could imagine a system of morality which requires you to obey the written laws in your country. Such a system would be a version of moral relativism, as different individuals would be required to follow different laws, but the moral facts are physical facts about the world, not mental facts, so they are metaphysically ordinary. Thus, different versions of moral relativism might be considered anti-realist or realist.
Epistemic anti-realism Just as moral anti-realism asserts the nonexistence of normative facts, epistemic anti-realism asserts the nonexistence of facts in the domain of
epistemology. Thus, the two are now sometimes grouped together as "metanormative anti-realism". Prominent defenders of epistemic anti-realism include
Hartry Field,
Simon Blackburn, Matthew Chrisman, and
Allan Gibbard, among others. ==See also==