Philosophical realism – usually not treated as a position of its own but as a stance towards other subject matters – is the view that a certain kind of thing (ranging widely from abstract objects like numbers to moral statements to the physical world itself) has mind-independent existence, i.e. that it exists even in the absence of any mind perceiving it or that its existence is not just a mere appearance in the eye of the beholder. This includes a number of positions within epistemology and metaphysics which express that a given thing instead exists independently of knowledge, thought, or understanding. This can apply to items such as the physical world, the past and future, other minds, and the self, though may also apply less directly to things such as universals, mathematical truths, moral truths, and thought itself. However, realism may also include various positions which instead reject metaphysical treatments of reality entirely.
Realism can also be a view about the properties of reality in general, holding that reality exists independent of the mind, as opposed to non-realist views (like some forms of skepticism and solipsism) which question the certainty of anything beyond one's own mind. Philosophers who profess realism often claim that truth consists in a correspondence between cognitive representations and reality.
Realists tend to believe that whatever we believe now is only an approximation of reality but that the accuracy and fullness of understanding can be improved. In some contexts, realism is contrasted with idealism. Today it is more usually contrasted with anti-realism, for example in the philosophy of science.
The oldest use of the term "realism" appears in medieval scholastic interpretations and adaptations of ancient Greek philosophy.
Etymology
The term comes from Late Latin realis "real" and was first used in the abstract metaphysical sense by Immanuel Kant in 1781 (CPR A 369).
Varieties
Metaphysical realism
Metaphysical realism maintains that "whatever exists does so, and has the properties and relations it does, independently of deriving its existence or nature from being thought of or experienced." In other words, an objective reality exists (not merely one or more subjective realities).
Naive or direct realism
Naive realism, also known as direct realism, is a philosophy of mind rooted in a common sense theory of perception that claims that the senses provide us with direct awareness of the external world. In contrast, some forms of idealism assert that no world exists apart from mind-dependent ideas and some forms of skepticism say we cannot trust our senses. The naive realist view is that objects have properties, such as texture, smell, taste and colour, that are usually perceived absolutely correctly. We perceive them as they really are.
Immanent realism
Is the ontological understanding which holds that universals are immanently real within particulars themselves, not in a separate realm, and not mere names. Most often associated with Aristotle and the Aristotelian tradition.
Scientific realism
Scientific realism is, at the most general level, the view that the world described by science is the real world, as it is, independent of what we might take it to be. Within philosophy of science, it is often framed as an answer to the question "how is the success of science to be explained?" The debate over what the success of science involves centers primarily on the status of unobservable entities apparently talked about by scientific theories. Generally, those who are scientific realists assert that one can make reliable claims about unobservables (viz., that they have the same ontological status) as observables. Analytic philosophers generally have a commitment to scientific realism, in the sense of regarding the scientific method as a reliable guide to the nature of reality. The main alternative to scientific realism is instrumentalism.