The Problems of Philosophy

by Bertrand Russell

All this seems to be so evident as to be hardly worth stating, except in answer to a man who doubts whether I know anything.

If we say that the things known must be in the mind, we are either unduly limiting the mind's power of knowing, or we are uttering a mere tautology.

'Laws of Thought'. They are as follows: (1) The law of identity: 'Whatever is, is.' (2) The law of contradiction: 'Nothing can both be and not be.' (3) The law of excluded middle: 'Everything must either be or not be.'

Against this absolute scepticism, no logical argument can be advanced.

many men, under the influence of science or of practical affairs, are inclined to doubt whether philosophy is anything better than innocent but useless trifling, hair-splitting distinctions, and controversies on matters concerning which knowledge is impossible.