C. Response to the Arguments for Thomas’ Opinion

196. From this is plain the solution to the deduction for the opinion [of Thomas, n.186]; for the authority of the Philosopher in On the Soul [ibid.] only proves that heat is an instrument of soul in this last way [n.195], namely because it digests and alters food, so that at the end of the alteration a substance can be generated from it. Hence two actions are there and two principles of acting: because with respect to the previous alteration the principle of acting is heat, but with respect to the form of the flesh to be induced the soul or the form of flesh is the principle; and the first agent is said to be an instrument with respect to the second, not properly by subordination of virtue to virtue, but by subordination of effect to effect; hence it would more properly be called a dispositive agent than an instrumental agent.

197. And when it is said further in the deduction [n.186] that the accidents act in virtue of substance, what follows is only that they are instruments; but they are not instruments of a non-entity substance; wherefore from this the opposite follows [sc. that the separated accidents do not act in virtue of substance].

198. And when the further inference is drawn [n.186] that the action of the accidents has a term not only at the accidental form but at the substantial form - this I reckon to be false, save as at a remote term, which is in no way attained by the action of the accidental form but is what the term is ordered to that is attained by the action of the accident.

199. And when the proof is given [n.186] that the accident attains the term of the action because it reaches the passive thing into which the form is induced, while the substance cannot attain the matter as passive object on which to act because it is not separated from the passions by virtue of a natural agent (as said in On Generation 1.3.317b20-33) - I say that this consequence does not hold save in virtue of the following implicitly understood proposition, that ‘every instrument attains the term of the principal agent’, which is false in the issue at hand.

200. And when this seems to be proved by what he adds, that ‘generation is the term of alteration’ [n.186] - this proof can be drawn to the opposite. For generation is not the intrinsic term of alteration, but an extrinsic one is and of a different genus, and generation has its own term prior in genus to the proper term of alteration. But it does not follow that, because alteration has its own and sufficient causality with respect to what is essentially posterior, it has a causality by which it attains what is essentially prior; rather the opposite follows, namely that it does not have a causality by which it attains what is essentially prior. Therefore, in the way in which generation is the term of alteration, what follows is that the principle of alteration does not attain the term of generation save mediately, because it attains something that is ordered toward it.