Berkeley is most importantly a philosopher, the second of the three British Empiricists, following John Locke and preceding David Hume. AN ESSAY TOWARDS A NEW THEORY OF VISION was published in 1709, one year before his first important philosophical work, A TREATISE CONCERNING THE PRINCIPLES OF HUMAN KNOWLEDGE. Yet the ESSAY is not primarily a philosophical work. It is a study of visual perception which is best classed with experimental psychology. Its major objective is to show how we perceive the distance and size of objects and their spatial relation to other objects. In so doing, Berkeley manages to criticize most of the accepted views on the topic. The last part of the ESSAY is a consideration of the difference between perception by sight and by touch and of whether we ever perceive the same thing by both faculties. It is in his treatment of this latter issue that Berkeley hints at the philosophical doctrines which he soon elaborated.
Most of the standard discussions of vision in Berkeley’s day were couched in terms of geometric diagrams showing how light rays converged and diverged when they passed through lenses or were reflected from surfaces of varying curvature. It was claimed that distance was estimated on the basis of the angle at which light entered the eye. His criticisms of such views give the first insight into the special character of Berkeley’s concern. He says that the perception of distance cannot be explained by lines and angles because we never perceive any such things and those who know nothing of optics perceive distance without ever thinking of such lines and angles. Berkeley wants to know what we perceive immediately which allows us to say that something is near or far away. Nor will he allow us to say we perceive the distance between us and an object. We estimate it on the basis of our immediate perceptions. There are three we typically use: first, the sensation we get when we cross our eyes to see something very close; second, the confused appearance of an object as it gets close to the eye, and third, the muscular strain involved in preventing, temporarily, the confused appearance of an object close to the eye. In addition to these we use our knowledge of the size, number, kind, and so on, of the objects in question. There is no necessary connection between these perceptions and the distance of objects. We have found the connection in experience and this gives rise to a habitual or customary connection between these two kinds of ideas. Visual perceptions are signs of distance and are related to it in the way a blush is to shame, or a word to the idea it stands for.
The more usual features of Berkeley’s doctrine come to the fore when he explains how it is that we experience the visual sign and its connection with the distance it signifies. The idea of distance comes from touch. He insists that what we really mean when we say that an object is at a distance is that certain...
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