When we perceive any object of a familiar kind, much of what appears subjectively to be immediately given is really derived from past experience.

Science is what you know, philosophy is what you don't know.

I say quite deliberately that the Christian religion, as organized in its Churches, has been and still is the principal enemy of moral progress in the world.

Many orthodox people speak as though it were the business of sceptics to disprove received dogmas rather than of dogmatists to prove them. This is, of course, a mistake.

To a modern mind, it is difficult to feel enthusiastic about a virtuous life if nothing is going to be achieved by it.

Mathematics, rightly viewed, possesses not only truth, but supreme beauty-a beauty cold and austere ... yet sublimely pure and capable of stern perfection such as only the greatest art can show.

When we look at a rock what we are seeing is not the rock, but the effect of the rock upon us.