The question of the nature and plausibility of realism arises with respect to a large number of subject matters, including ethics, aesthetics, causation, modality, science, mathematics, semantics, and the everyday world of macroscopic material objects and their properties. Although it would be possible to accept (or reject) realism across the board, it is more common for philosophers to be selectively realist or non-realist about various topics: thus it would be perfectly possible to be a realist about the everyday world of macroscopic objects and their properties, but a non-realist about aesthetic and moral value. In addition, it is misleading to think that there is a straightforward and clear-cut choice between being a realist and a non-realist about a particular subject matter. It is rather the case that one can be more-or-less realist about a particular subject matter. Also, there are many different forms that realism and non-realism can take.
The question of the nature and plausibility of realism is so controversial that no brief account of it will satisfy all those with a stake in the debates between realists and non-realists. This article offers a broad brush characterisation of realism, and then fills out some of the detail by looking at a few canonical examples of opposition to realism. The discussion of forms of opposition to realism is far from exhaustive and is designed only to illustrate a few paradigm examples of the form such opposition can take.
There are two general aspects to realism, illustrated by looking at realism about the everyday world of macroscopic objects and their properties. First, there is a claim about existence. Tables, rocks, the moon, and so on, all exist, as do the following facts: the table’s being square, the rock’s being made of granite, and the moon’s being spherical and yellow. The second aspect of realism about the everyday world of macroscopic objects and their properties concerns independence. The fact that the moon exists and is spherical is independent of anything anyone happens to say or think about the matter. Likewise, although there is a clear sense in which the table’s being square is dependent on us (it was designed and constructed by human beings after all), this is not the type of dependence that the realist wishes to deny. The realist wishes to claim that apart from the mundane sort of empirical dependence of objects and their properties familiar to us from everyday life, there is no further sense in which everyday objects and their properties can be said to be dependent on anyone’s linguistic practices, conceptual schemes, or whatever.
In general, where the distinctive objects of a subject-matter are a, b, c, … , and the distinctive properties are …is F, …is G, …is H and so on, realism about that subject matter will typically take the form of a claim like the following:
a, b, and c and so on exist, and the fact that they exist and have properties such as F-ness, G-ness, and H-ness is (apart from mundane empirical dependencies of the sort sometimes encountered in everyday life) independent of anyone’s beliefs, linguistic practices, conceptual schemes, and so on.
Non-realism can take many forms, depending on whether or not it is the existence or independence dimension of realism that is questioned or rejected. The forms of non-realism can vary dramatically from subject-matter to subject-matter, but error-theories, non-cognitivism, instrumentalism, nominalism, certain styles of reductionism, and eliminativism typically reject realism by rejecting the existence dimension, while idealism, subjectivism, and anti-realism typically concede the existence dimension but reject the independence dimension. Philosophers who subscribe to quietism deny that there can be such a thing as substantial metaphysical debate between realists and their non-realist opponents (because they either deny that there are substantial questions about existence or deny that there are substantial questions about independence).