Nothing can be more incorrect than the assumption one sometimes meets with, that physics has one method, chemistry another, and biology a third.

It is the first duty of a hypothesis to be intelligible.

Matter and force are the two names of the one artist who fashions the living as well as the lifeless.

Common sense is science exactly in so far as it fulfills the ideal of common sense; that is, sees facts as they are, or at any rate, without the distortion of prejudice, and reasons from them in accordance with the dictates of sound judgment. And science is simply common sense at its best, that is, rigidly accurate in observation, and merciless to fallacy in logic.

If the twentieth century is to be better than the nineteenth, it will be because there are among us men who walk in Priestley's footsteps....To all eternity, the sum of truth and right will have been increased by their means; to all eternity, falsehoods and injustice will be the weaker because they have lived.

A man's worst difficulties begin when he is able to do as he likes.

Teach a child what is wise, that is morality. Teach him what is wise and beautiful, that is religion!