You cannot have a rational discussion with a man who prefers shooting you to being convinced by you.

Science must begin with myths, and with the criticism of myths.

No particular theory may ever be regarded as absolutely certain.... No scientific theory is sacrosanct.

In so far as a scientific statement speaks about reality, it must be falsifiable; and in so far as it is not falsifiable, it does not speak about reality.

I think that we shall have to get accustomed to the idea that we must not look upon science as a 'body of knowledge,' but rather as a system of hypotheses; that is to say, as a system of guesses or anticipations which in principle cannot be justified, but with which we work as long as they stand up to tests, and of which we are never justified in saying that we know they are 'true' or 'more or less certain' or even 'probable.'

If you can't say it simply and clearly, keep quiet, and keep working on it till you can.

Optimism is a duty. The future is open. It is not predetermined. No one can predict it, except by chance. We all contribute to determining it by what we do. We are all equally responsible for its success.