The Art of Medicine

are substantial. But since we labor under a scarcity of these, they must be sought elsewhere: namely, from the proper accident, the causes, the effects, or the offices, and from the parts of the thing to be defined. These do not distinguish the substances of things otherwise than true differences do, but they express their nature and force less clearly. Where, therefore, a substantial difference is lacking, we use a proper accident. I say "proper" when it is convertible with the thing to be defined and shows its property and affection: such as laughing or weeping. This is distinct from a true difference A because the latter not only distinguishes one thing from another but also expresses its nature, whereas the proper accident merely shows an affection. For a human is a human because he reasons, not because he laughs or weeps. Differences are sought from causes. One cause is efficient, another is material, another formal, another final. The efficient cause, as Aristoteles Aristotle defines it, is that which first moves. We, using the term more broadly, say that the efficient cause is not only that from which motion first arises, but simply that which provides the labor for the thing to be made, whether primarily and in itself, or in a second place and by accident, or as an instrument. This is what Galenus Galen also appears to believe in Book 1 of De locis affectis On Affected Parts. B His words are: "That by touching which we are affected, and by the removal of which the affection ceases, is, among all men, acknowledged to be the cause."