The Enlightenment Period
What was George Berkeley’s new theory of vision?
Berkeley, like René Descartes (1596–1650), sought to account for the perception of distance. Descartes had claimed in his Dioptrics (1647) that an innate knowledge of geometry enables even those who have never studied geometry to calculate distance by figuring out the height of a triangle formed by light rays from the visible object to each eye. Berkeley built on Irish natural philosopher William Molyneux’s (1656–1698) claim that distance, as a length from the object to the eye, cannot itself be seen. Berkeley reasoned that since what is seen is a two-dimensional object, its relation to distance is contingent, dependent on sensations in the eyes and associations in the mind between what has been touched and what is seen. These associations depend on past experience.
The overall result of Berkeley’s reasoning about how vision works is that visual perception is an active, learned process. He also claimed, against John Locke (1632–1704), that there are no general ideas common to both sight and touch.