We know a great deal, but our ignorance is sobering and boundless. With each step forward, with each problem which we solve, we not only discover new and unsolved problems, but we also discover that where we believed that we were standing on firm and safe ground, all things are, in truth, insecure and in a state of flux.

Ignorance is not a simple lack of knowledge but an active aversion to knowledge, the refusal to know, issuing from cowardice, pride, or laziness of mind.

It must be possible for an empirical system to be refuted by experience.

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

We do not know anything - this is the first. Therefore, we should be very modest - this is the second. Not to claim that we do know when we do not - this is the third. That's the kind of attitude I'd like to popularize. There is little hope for success.

What really makes science grow is new ideas, including false ideas.

The history of science is everywhere speculative. It is a marvelous hiatory. It makes you proud to be a human being.