Sue asked:

Berkeley suggests that material things do not exist unless they are perceived. What then, by
Berkeley's definition, exists in the world of a blind man?

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The fallacy revealed in your question is to draw the conclusion that perception only refers to seeing.
Berkeley, like Locke and Hume, was an empiricist, like them he believed that knowledge of the world
came through the senses: a blind man, therefore, deprived of one sense would rely on the rest of his
senses to provide an awareness of the world. The same mistake is often made about memory, we
often struggle to visualise a past event when it is in some cases more easily accessible through taste,
scent, sound or feel.

Berkeley, though an empiricist, differed from Locke and Hume in so much as he was an empirical
idealist,as opposed to their 'material ' empiricism, an acknowledgement of substances in an 'outside
world.' which could generate sensations. The world to Berkeley was made up of ideas derived from
information accessed through the senses. He never denied that we could smell things, taste things,
feel things or hear things. However, everything stemmed from the will of the person: he ingeniously
formulated a denial of causality from the supposed outside world by claiming that the thing which
Locke, for instance, claimed to be matter would be, in a way, stagnant and unable to causeanything.
To cause is to act and nothing is genuinely active but the will of an intelligent being. We interpret
sensations from which we subsequently form ideas; which is somehow a reversal of the notion that
things ' out there ' impose themselves upon us.

Berkeley would claim that an apple is a collection of ideas composed of colour, shape, texture,
aroma, taste. There is no need to postulate that all this is somehow attached to an inaccessible
material thing in some sort of external world. In line with Berkeley's notion of reality a blind man would
have no difficulty in identifying an apple.

John Brandon

Berkeley did not suggest but rather arguedfor the view that to be is to be perceived: things can be
analyzed without remainder into their qualities (e.g., shape, color, texture, smell, etc.) and that a
quality could exist apart from a subject who is experiencing it is absurd. What exists in the world of
the blind is exactly what exists in the world of those with sight, for that same world is sustained by
God's perception of it.

Tony Flood

Everything that he perceives (touches, smells, hears, tastes) — perception can be through any of the
senses. But don't forget that Berkeley thought that god perceived everything in the universe all the
time, so that the existence of things doesn't depend on their perception by individual humans.

Tim Sprod