IB Philosophy 3.2.2 Theories of Perception Key Definitions

Arguments from illusion highlight how our senses can present the world as being other than it actually is, as when a straight stick appears bent in water or a white wall looks pink under coloured lighting. These cases are taken to show that what we directly perceive are sense data or mental representations rather than physical objects themselves, motivating indirect realist and idealist theories of perception.

Direct realism (also called naive realism) holds that perception gives us unmediated access to the external world as it really is. The objects of perception are the physical things themselves, not mental representations or sense data.

Idealism is the metaphysical and epistemological thesis that reality is fundamentally mental or mind-dependent, so that physical objects either reduce to collections of ideas or exist only insofar as they are perceived. Developed by Berkeley and later by Hegel, the view challenges common-sense realism by arguing that we can never step outside experience to verify an independently existing material world.

Epistemological idealism is the view that reality is fundamentally mental or mind-dependent. In its strongest form, associated with Berkeley, physical objects exist only as collections of perceptions, and there is no mind-independent material world.

Nietzsche's perspectivism holds that all knowledge and value judgments arise from a particular perspective, shaped by the interests, drives, and circumstances of the knower, with no neutral 'view from nowhere' from which to evaluate claims absolutely. This does not collapse into relativism, since Nietzsche still distinguishes between life-affirming and life-denying perspectives.

Phenomenalism holds that statements about physical objects are ultimately reducible to statements about actual and possible sensory experiences, so that to say a table exists is just to say that certain visual and tactile sensations would occur under appropriate conditions. The view avoids metaphysical commitments about unobservable matter but struggles to account for unexperienced objects and the regularity of nature.

Realism in epistemology and metaphysics holds that the external world exists independently of our perception or beliefs about it, and that our senses, when functioning properly, give us at least partially accurate access to this mind-independent reality. The position underpins everyday and scientific reasoning but must answer sceptical challenges about how we can verify the correspondence between our experiences and the world as it actually is.

sensory properties such as colour, sound, taste, smell, and warmth that Descartes and Locke argue do not inhere in external objects but exist only as experiences produced in a perceiving mind. Unlike primary qualities (extension, shape, motion), secondary qualities are mind-dependent responses to the physical micro-structure of matter and tell us less about the objective nature of things than about our own sensory apparatus.