Nicomachean Ethics

...we might perfect ourselves, and then rule others: and thus a threefold doctrine of active philosophy, concerning a threefold manner of living, is handed down by the Philosopher, and accordingly it is sufficiently divided into three parts, as was said. But having provided the definition of philosophy and its division, we must now consider the intention of the Philosopher in the book of Morals, the utility of the doctrine, whether the book belongs to that author to whom it is said to belong, and moreover the title and the order which this faculty has in relation to other sciences. Furthermore, it seems not only useful but even necessary to consider diligently the division of the books, to which part of philosophy this moral branch is reduced, and finally the very method of the doctrine; wherefore let us consider each of these, as is customary.

First, therefore, the intention of Aristotle in this book of Morals is to teach those things by which a man may become happy—with human happiness indeed, so far as is possible. For since human happiness, in his opinion, is activity according to virtue, he has most exactly handed down the doctrine concerning it and the virtues, and all the means which, in his judgment, lead to the attainment of such happiness, so that by acquiring the virtues for ourselves, and then by acting according to them, we may live a happy life so far as is possible. The utility of this book can be easily perceived from the foregoing, as well as from those things which shall be said; for just as the science of medicine relates to the health of the body, so moral doctrine is seen to relate to the health of the soul. For this shows us the way and the method by which we can obtain and achieve virtue and happiness itself, in which the health of the soul is contained.

Hardly anyone doubts that this book is Aristotle’s; for indeed not only the Peripatetics, but also nearly all the Platonists confess it to be his, and they extol it with wonderful praises. Aristotle himself also mentions this work in certain places as his own; furthermore, the method, the character, and the very order of writing altogether...