After we came out of the church, we stood talking for some time together of Bishop Berkeley's ingenious sophistry to prove the nonexistence of matter, and that every thing in the universe is merely ideal. I observed, that though we are satisfied his doctrine is not true, it is impossible to refute it. I never shall forget the alacrity with which Johnson answered, striking his foot with mighty force against a large stone, till he rebounded from it "I refute it thus."
James Boswell: The Life of Samuel Johnson, LL.D. (1791)
The world is composed of matter: wind, water, and hard things like rocks that can be kicked by philosophers, whereas our awareness of the world seems to be of an altogether different character. Consciouslness, except our own, cannot be seen, heard, tasted, touched or smelled or otherwise directly shared, but can only be intimated by words, the meanings of which we learn ostensively, by reference to things that can be observed by both speaker and hearer.
The challenge of explaining consciousness has naturally attracted the attention of philosophers who seem almost as puzzled by the problem as anyone else. A solution that some philosophers have adopted is to assume that consciousness is inherent in all matter, not just brains, a theory called panpsychism.
