Didascalicon, Book I (chapters 2-13): the origin of the arts and the division of philosophy
Chapter V. What things pertain to philosophy
But as I see, we have already fallen into an inextricable labyrinth by the very order of our speaking, where not a tangled discourse but an obscure matter causes us difficulty. For since we have undertaken to speak of the study of wisdom, and have testified that it belongs by a certain privilege of nature to men alone, we seem consequently now to have posited a certain wisdom as the governor of all human acts. For if the nature of brute animals, which is ruled by no judgment of reason, pours out its movements according to the impulses of the senses alone, and in seeking or fleeing anything does not use the discernment of intelligence but is driven by a certain blind affection of the flesh, it remains that the act of the rational soul is not taken hold of by blind desire, but that wisdom as governor always goes before. If this is established as true, we say that not only those studies in which the nature of things or the discipline of morals is treated, but also the principles of all human acts or studies, belong, not inappropriately, to philosophy. According to this acceptation we can define philosophy thus: “Philosophy is the discipline that fully investigates the reasons of all things, human and divine.” Nor should it trouble us that we said above that philosophy is the love and study of wisdom: not of that wisdom which is unfolded in instruments, such as architecture, agriculture and the like, but of that wisdom which alone is the primeval reason of things. For the same act can both belong to philosophy according to its principle, and be excluded from it according to its administration. For example, to speak of the present matter: the principle of agriculture belongs to the philosopher, its administration to the farmer. Besides, the works of craftsmen, although they are not nature, nevertheless imitate nature, and express by reason the form of their exemplar, which is nature, whom they imitate. You see now by what reasoning we are compelled to spread philosophy into all the acts of men, so that there must needs be as many parts of philosophy as there are diversities of things to which it is established that it pertains.