A theory which is not refutable by any conceivable event is non-scientific. Irrefutability is not a virtue of a theory (as people often think) but a vice.

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.

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

I see now more clearly than ever before that even our greatest troubles spring from something that is [as] admirable and sound as it is dangerous – from our impatience to better the lot of our fellows.

It is not his possession of knowledge, of irrefutable truth, that makes the man of science, but his persistent and recklessly critical quest for truth.

It is complete nihilism to propose laying down arms in a world where atom bombs are around. It is very simple: there is no way of achieving peace other than with weapons.

Now this principle of induction cannot be a purely logical truth like a tautology or an analytic statement. . . .