It is by his activities and not by enjoyment that man feels he is alive. In idleness we not only feel that life is fleeting, but we also feel lifeless.

A categorical imperative would be one which represented an action as objectively necessary in itself, without reference to any other purpose.

The wise man can change his mind; the stubborn one, never.

Human reason has this peculiar fate that in one species of its knowledge it is burdened by questions which, as prescribed by the very nature of reason itself, it is not able to ignore, but which, as transcending all its powers, it is also not able to answer.

The science of mathematics presents the most brilliant example of how pure reason may successfully enlarge its domain without the aid of experience

The desire which a man has for a woman is not directed towards her because she is a human being, but because she is a woman ; that she is a human being is of no concern to the man; only her sex is the object of his desires.

Freedom in the practical sense is the independence of the power of choice from necessitation by impulses of sensibility