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.

How did George Berkeley's theory of vision relate to the concept of matter and physical existence?

Berkeley is well known for his theory of vision that contributed so much to modern psychology of perception. However, in that theory he completely repudiated the primary bastion of empiricism: namely, matter. Berkeley departed from both common sense and science in elaborately insisting that matter—the entire physical world— based on our best evidence, simply did not exist in the way that the other empiri-

Why is George Berkeley considered either an aberration or an obstacle?

Berkeley is an aberration insofar as his ideas defy common sense to the point of being dismissible as simple absurdities. He is an obstacle insofar as he founded a powerful and enduring school of thought that dominated some areas of philosophy in the nineteenth century and evolved into very perplexing progressive movements in the twentieth and, it now seems, twenty-first centuries.

cists—Hobbes, Locke and Hume, and later on, John Stuart Mill and Bertrand Russell—assumed that it did. For any serious student of the history of philosophy, Berkeley is either a delightful aberration or an intractable obstacle because of this position.

To whom is Berkeley's idealism perplexing?

To those who continue to cleave to the reality of the perceived existence of an external world, Berkeley's idealism can be perplexing. It is also a problematic position for many scientists, who must believe in an "objective reality" in order for their work concerning "objective facts" to make sense.

What did George Berkeley mean when he said, "To be is to be perceived"?

In Berkeley's view of what exists in the world, there are only three things: minds, ideas, and God. Angels are also minds, and another way of dividing up the world is into spirits and ideas. Human beings, angels, and God are spirits. Everything else is ideas. Nothing else is known to exist. But, if only spirits and ideas exist, how can there be a world?

Berkeley thought that what we think of as an external world is just one idea added to our ideas of sense. No idea of sense can exist without being perceived by some mind. Berkeley's motto was esse estpercipi, or, "To be is to be perceived." The idea of an external world is an isolated idea in itself, but no more than an idea. Furthermore, many of the ideas that we think we have, which support the existence of external reality, are no more than special distinct ideas combined with ideas of sense. For example, the ideas "reality" and "physical matter" are just words to which nothing like an external world corresponds. At best, they are merely additional ideas. This doctrine that reality is just another idea, in Berkeley's sense, is what made him the philosophical idealist par excellence.

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