Realism (philosophy), in philosophy, a term used for two distinct doctrines of epistemology.

In modern philosophy, it is applied to the doctrine that ordinary objects of sense perception, such as tables and chairs, have an existence independent of their being perceived. In this sense, it is contrary to the idealism of philosophers such as George Berkeley or Immanuel Kant. In its extreme form, sometimes called naive realism, the things perceived by the senses are believed to be exactly what they appear to be. In more sophisticated versions, sometimes referred to as critical realism, some explanation is given of the relationship between the object and the observer that accounts for the possibility of illusion, hallucination, and other perceptual errors.

In medieval philosophy, the term realism referred to a position that regarded Platonic Forms, or universals, as real. That position is now usually called Platonic realism. In Plato's philosophy, a common noun, such as bed, refers to the ideal nature of the object, which is conveyed by its definition, and this ideal nature has metaphysical existence independent of the particular objects of that type. Thus, circularity exists independent of particular circles; justice, independent of particular just individuals or just states; and “bedness,” independent of particular beds. In the Middle Ages, this position was defended against nominalism, which denied the existence of such universals. Nominalists asserted that the many objects called by one name shared nothing but the name. Compromises between these two positions included moderate realism, which claimed that the universal existed in the many objects of the same type but not independent of them, and conceptualism, which held that the universal might exist independent of the many objects of that particular type, but only as an idea in the mind, not as a self-subsisting metaphysical entity.