One of the most painful circumstances of recent advances in science is that each one makes us know less than we thought we did

It seems to me a fundamental dishonesty, and a fundamental treachery to intellectual integrity to hold a belief because you think it's useful and not because you think it's true.

Morality in sexual relations, when it is free from superstition, consists essentially in respect for the other person, and unwillingness to use that person solely as a means of personal gratification, without regard to his or her desires.

We know very little, and yet it is astonishing that we know so much, and still more astonishing that so little knowledge can give us so much power.

Physics, owing to the simplicity of its subject matter, has reached a higher state of development than any other science.

Bad philosophers may have a certain influence; good philosophers, never.

Any pleasure that does no harm to other people is to be valued.