I have come to the conclusion that Darwinism is not a testable scientific theory, but a metaphysical research programme.

. . . it seems to me certain that more people are killed out of righteous stupidity than out of wickedness.

It is wrong to think that belief in freedom always leads to victory; we must always be prepared for it to lead to defeat. If we choose freedom, then we must be prepared to perish along with it.

Rationalism is an attitude of readiness to listen to contrary arguments and to learn from experience... of admitting that "I may be wrong and you may be right and, by an effort, we may get nearer the truth."

The growth of knowledge depends entirely upon disagreement.

The best thing that can happen to a human being us to find a problem, to fall in love with that problem, and to live trying to solve that problem, unless another problem even more lovable appears.

In my view, aiming at simplicity and lucidity is a moral duty of all intellectuals: lack of clarity is a sin, and pretentiousness is a crime.