Contradiction is not a sign of falsity, nor the lack of contradiction a sign of truth.

Men never do evil so completely and cheerfully as when they do it from religious conviction.

As we speak of poetical beauty, so ought we to speak of mathematical beauty and medical beauty. But we do not do so; and that reason is that we know well what is the object of mathematics, and that it consists in proofs, and what is the object of medicine, and that it consists in healing. But we do not know in what grace consists, which is the object of poetry.

If they [Plato and Aristotle] wrote about politics it was as if to lay down rules for a madhouse. And if they pretended to treat it as something really important it was because they knew that the madmen they were talking to believed themselves to be kings and emperors. They humored these beliefs in order to calm down their madness with as little harm as possible.

Habit is a second nature, which destroys the first.

Let each of us examine his thoughts

Man's sensitivity to the little things and insensitivity to the greatest are the signs of a strange disorder.