Didascalicon, Book I (chapters 2-13): the origin of the arts and the division of philosophy
Chapter IX. In what man is like God
There are two things that restore the divine likeness in man, that is, the contemplation of truth and the exercise of virtue; for in this respect man is like God, though man is wise and just mutably, and God immutably. Of those actions, moreover, which serve the necessities of this life, there are three kinds. The first administers the instrument of nature; the second guards against the troubles which can befall from outside; the third provides a remedy against those already inflicted. When, therefore, we aim at restoring our nature, the action is divine; but when we provide what is necessary for that which is weak in us, it is human. Every action, then, is either divine or human. We may not unfittingly call the former (because it concerns higher things) understanding, and the latter (because it concerns lower things and needs, as it were, a kind of counsel) knowledge. If, therefore, wisdom, as was said above, governs all the actions that are done by reason, it follows that we should say wisdom contains these two parts, namely understanding and knowledge. Again, understanding, since it labors both in the investigation of truth and in the consideration of morals, we have divided into two: into the theoretical, that is the speculative, and the practical, that is the active, which is also called ethical, that is moral. Knowledge, on the other hand, because it pursues human works, is fittingly called mechanical, that is, adulterate.