It is wrong for a man to say that he is certain of the objective truth of any proposition unless he can produce evidence which logically justifies that certainty.

The secret of genius is to carry the spirit of childhood into maturity.

The foundation of all morality is to have done, once and for all, with lying; to give up pretending to believe that for which there is no evidence, and repeating unintelligible propositions about things beyond the possibilities of knowledge.

It is not to be forgotten that what we call rational grounds for our beliefs are often extremely irrational attempts to justify our instincts.

That man, I think, has had a liberal education, who has been so trained in youth that his body is the ready servant of his will.

Every great advance in natural knowledge has involved the absolute rejection of authority.

The dogma of the infallibility of the Bible is no more self-evident than is that of the infallibility of the popes.