Fundamental Principles of the Metaphysics of Morals

by Immanuel Kant

Ancient Greek philosophy was divided into three sciences: physics, ethics, and logic.

All rational knowledge is either material or formal: the former considers some object, the latter is concerned only with the form of the understanding and of the reason itself, and with the universal laws of thought in general without distinction of its objects. Formal philosophy is called logic.

the former, however, being laws according to which everything does happen; the latter, laws according to which everything ought to happen.