Nothing puts a greater obstacle in the way of the progress of knowledge than thinking that one knows what one does not yet know.

Here take back the stuff that I am, nature, knead it back into the dough of being, make of me a bush, a cloud, whatever you will, even a man, only no longer make me.

One's first step in wisdom is to question everything - and one's last is to come to terms with everything.

Do not say hypothesis, and even less theory: say way of thinking.

Prejudices are so to speak the mechanical instincts of men: through their prejudices they do without any effort many things they would find too difficult to think through to the point of resolving to do them.

I have never yet met anyone who did not think it was an agreeable sensation to cut tinfoil with scissors.

If we make a couple of discoveries here and there we need not believe things will go on like this for ever. Just as we hit water when we dig in the earth, so we discover the incomprehensible sooner or later.