The standard opposition between those who affirm, and those who deny, the real existence of some kind of thing, or some kind of fact or state of affairs. Almost any area of discourse may be the focus of this dispute: the external world, the past and future, other minds, mathematical objects, possibilities, universals, and moral or aesthetic properties are examples. A realist about a subject-matter S may hold

1. (i) that the kinds of thing described by S exist;

2. (ii) that their existence is independent of us, or not an artefact of our minds, or our language or conceptual scheme;

3. (iii) that the statements we make in S are not reducible to other kinds of statement, revealing them to be about some different subject-matter;

4. (iv) that the statements we make in S have truth conditions, being straightforward descriptions of aspects of the world and made true or false by facts in the world;

5. (v) that we are able to attain truths about S, and that it is appropriate fully to believe things we claim in S.

Different oppositions focus on one or another of these claims. Eliminativists think the S discourse should be rejected. Sceptics either deny (i) or deny our right to affirm it. Idealists and conceptualists deny (ii), reductionists deny (iii), while instrumentalists and projectivists deny (iv). Constructive empiricists deny (v). Other combinations are possible, and in many areas there is little consensus on the exact way a realist/anti-realist dispute should be constructed. One reaction is that realism attempts to ‘look over its own shoulder’, i.e. that it believes that as well as making or refraining from making statements in S, we can fruitfully mount a philosophical gloss on what we are doing as we make such statements, and philosophers of a verificationist tendency have been suspicious of the possibility of this kind of metaphysical theorizing: if they are right, the debate vanishes, and that it does so is the claim of minimalism. The issue of the method by which a genuine realism can be distinguished is therefore critical.

One influential suggestion, associated with Dummett, is borrowed from the intuitionistic critique of classical mathematics, and suggests that the unrestricted use of the principle of bivalence is the trademark of realism. However, this has to overcome counterexamples both ways: although Aquinas was a moral realist, he held that moral reality was not sufficiently structured to make true or false every moral claim, while Kant believed that we could use the law of bivalence happily in mathematics precisely because it was only our own construction. Realism can itself be subdivided: Kant, for example, combines empirical realism (within the phenomenal world the realist says the right things—surrounding objects really exist and are independent of us and our mental states) with transcendental idealism (the phenomenal world as a whole reflects the structure imposed on it by the activity of our minds as they render it intelligible to us). In modern philosophy the orthodox opposition to realism has been from philosophers such as Goodman impressed by the extent to which we perceive the world through conceptual and linguistic lenses of our own making. See also pragmatism, quasi-realism.