Perception, in philosophical usage, may mean internal perception, the apprehension of any modification of consciousness; but it usually refers to external perception, the recognition of an external object by means of the senses—something more than sensation, and including an element of judgment or the comparing power.
Two great disputes connect themselves with perception, both raised into prominence by Berkeley. The first is the origin of our judgments of the distances and real magnitudes of visible bodies; Berkeley maintaining, in opposition to the common opinion on this subject, that these were learned by experience, and not known by the mere act of vision (see VISION). The second question relates to the grounds we have for asserting the existence of an external and material world. See BERKELEY, KANT, REID; also PSYCHOLOGY, PHILOSOPHY.