Sitar asked:

I read Berkeley's Three Dialogues Between Hylas and Philonous.

I would just like to know what do you feel. When asked how to refute Berkeley, Samuel Johnson
kicked a stone and said, "I refute him thus." Was this really a refutation of Berkeley? Why, or why
not?

Also what is the difference between Berkeley's idealism and Epicurus' materialism?

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Berkeley's metaphysics has the great merit of being effectively summed up in three words, albeit
three words of Latin: Esse est percipi,or 'To be is to be perceived'. By this he meant to deny that the
objects of the external world have any material existence; they exist only as ideas, the same ideas
which we have of them when we perceive them. Because only ideas are taken to exist this view is
called idealism.

The mistake which is attributed to Johnson in this famous anecdote is to confuse perception with
sight alone. Had Berkeley supposed (absurdly) that physical objects existed only in our visual
perceptions of them, then apprehending an object in a non-visual way (kicking it, for instance) would
have sufficed to refute him. However, perception includes touch, and kicking is just a rough sort of
touching. So Johnson's stubbed toe is not a refutation of idealism.

Reflection on the 'virtual reality' of science fiction (and to some extent science fact) may help you to
understand how Berkeley's account of the world was supposed to work. Participants in a virtual
environment perceive apparently material objects which are actually just subroutines of the computer
program maintaining the environment. Moreover, were sufficiently strong artificial intelligence
available, the participants themselves could merely be extraordinarily sophisticated subroutines. The
world which they experienced could be as rich as ours, although it need not contain anything
'material'. The only external reality is the program itself, and the computer it runs on: in Berkeley's
metaphysics this role is played by God.

Where Berkeley sought to reduce the material to the mental, Epicurus attempted the exact opposite.
In his metaphysics all mental experiences are ultimately to be explained as the result of physical
interactions between material objects. The key similarity between the two systems is that they both
avoid the fundamental problem of a more intuitive dualism (in which both the mental and the material
are irreducible): explaining how the two modes of reality affect each other. An important difference is
that God is an essential and central feature of Berkeley's metaphysics, a feature which Epicurus
explicitly disavows. However, it is possible to reconstruct both systems as independent of the
existence of God.

Andrew Aberdein