The growth of knowledge depends entirely upon disagreement.

The true Enlightenment thinker, the true rationalist, never wants to talk anyone into anything. No, he does not even want to convince; all the time he is aware that he may be wrong. Above all, he values the intellectual independence of others too highly to want to convince them in important matters. He would much rather invite contradiction, preferably in the form of rational and disciplined criticism. He seeks not to convince but to arouse - to challenge others to form free opinions.

There is no pure, disinterested, theory-free observation.

If you know that things are bound to happen whatever you do, then you may feel free to give up the fight against them.

The use of violence is justified only under a tyranny which makes reforms without violence impossible, and should have only one aim, that is, to bring about a state of affairs which makes reforms without violence possible.

The survival value of intelligence is that it allows us to extinct a bad idea, before the idea extincts us.

I have spoken to Einstein and he admitted to me that his theory was in fact no different from the one of Parmenides.