Common sense is the most widely shared commodity in the world, for every man is convinced that he is well supplied with it.

When writing about transcendental issues, be transcendentally clear.

Even the mind depends so much on temperament and the disposition of one's bodily organs that, if it is possible to find a way to make people generally more wise and more skilful than they have been in the past, I believe that we should look for it in medicine. It is true that medicine as it is currently practiced contains little of much use.

I accept no principles of physics which are not also accepted in mathematics.

But I cannot forget that, at other times I have been deceived in sleep by similar illusions; and, attentively considering those cases, I perceive so clearly that there exist no certain marks by which the state of waking can ever be distinguished from sleep, that I feel greatly astonished; and in amazement I almost persuade myself that I am now dreaming.

Conquer yourself rather than the world.

Everybody thinks himself so well supplied with common sense that even those most difficult to please. . . never desire more of it than they already have.