realism, in philosophy, the viewpoint which accords to things which are known or perceived an existence or nature which is independent of whether anyone is thinking about or perceiving them.

Varieties of philosophical realism

The history of Western philosophy is checkered with disputes between those who have defended forms of realism and those who have opposed them. While there are certainly significant similarities linking the variety of positions commonly described as realist, there are also important differences which obstruct any straightforward general characterization of realism. Many, if not all, of these disputes may be seen as concerned in one way or another with the relations between, on the one hand, human beings as thinkers and subjects of experience and, on the other hand, the objects of their knowledge, belief, and experience. Do sense perception and other forms of cognition, and the scientific theorizing which attempts to make sense of their deliverances, provide knowledge of things which exist and are as they are independently of people’s cognitive or investigative activities? It is at least roughly true to say that philosophical realists are those who defend an affirmative answer to the question, either across the board or with respect to certain areas of knowledge or belief—e.g., the external world, scientific theories, mathematics, or morality.

The affirmative answer may seem no more than the merest common sense, because the vast majority of one’s beliefs are certainly most naturally taken to concern mind-independent objects whose existence is an entirely objective matter. And this seems to be so whether the beliefs in question are about mundane matters such as one’s immediate surroundings or about theoretical scientific entities such as subatomic particles, fundamental forces, and so on. Nevertheless, much argument and clarification of the issues and concepts involved (e.g., objectivity and mind-independence) is required if the realism favoured by common sense is to be sustained as a philosophical position.

Any general statement of realism, however, inevitably obscures the great variation in focus in controversies between realists and antirealists from antiquity to the present day. In some controversies, what is primarily at issue is a question of ontology, concerning the existence of entities of some problematic kind. In others, the opposition, while still broadly ontological in character, concerns rather the ultimate nature of reality as a whole, a historically important example being the controversies generated by various forms of idealism. In yet others the dispute, while not entirely divorced from questions of ontology, is primarily concerned with the notion of truth, either in general or in application to statements of some particular type, such as moral judgments or theoretical scientific claims about unobservable entities.

Realism in ontology

In application to matters of ontology, realism is standardly applied to doctrines which assert the existence of entities of some problematic or controversial kind. Even under this more restricted heading, however, realism and opposition to it have taken significantly different forms, as illustrated in the following three examples.