In this Chapter, Aristotle is speaking only about an active potency, which he has above said is “essentially and immediately” (per se primo) a potency. And this is quite clear from the course of the text and from the divisions which it gives, as well as from the clarification or the differentia-tion which it adds.
Metaphysics Book IX 167 Therefore, it can first be asked: what is a vital potency? And what is a non vital potency? For this division is suggested by the Philosopher when he says18 that certain potencies belong to the soul while others belong to inanimate things. Therefore, briefly it should be said that vital potencies are said to be all those which follow upon the soul inasmuch as it is a soul, or follow upon some grade of life. And because we do not conceive or distinguish a grade of life except by relation to a proper operation by which a living thing acts upon itself in order that it actuate itself or that it be perfected, therefore a vital potency is one which is a proximate and intrinsic principle of a vital operation by which a living thing perfects and actuates itself.
And within this genus, there can further be distinguished two poten-cies. One is a proximate principle by which a living thing perfects itself, but not according to that same potency. The second is what according to that same potency is a proximate principle of actuating itself. And this is properly a potency for an immanent activity, which potency is vital in a more perfect way. And this again is divided into rational and non–rational, which division Aristotle has more explicitly stated here.19
Question 2. About this, we can further ask whether the mentioned divi-sion is appropriate, as well as what is a rational potency and how many such potencies exist? These questions also belong to the science of the soul;20 and therefore we should say briefly that every potency which fol-lows upon the intellectual grade as such is called a rational potency, while every inferior potency can be called non–rational.
From this, two sorts of rational potency can be distinguished, the first eliciting or commanding and the second executing in subordination to that first potency. And this last can in a word be called “rational by com-mand” (imperative rationalis) according to the doctrine of the Philosopher in Book 1, Chapter 13 of his Ethics.21 In the first way that potency is called rational which is rational in itself and elicits an act in a rational way. This again can be subdistinguished. For one kind is formally or essentially the reason itself, that is the intellect; the second kind is rational by participa-tion, or through concomitance and governance (regimen), for example, the will. And Aristotle is speaking of both in this place because both fol-low from the grade of being rational. Or rather the Philosopher seems to speak about them in the manner of one thing for the reason that from the two there is perfected a kind of single adequate principle of human actions insofar as one moves with respect to exercise and the other with respect to specification. That is called a “rational by command” potency which, although in itself it is not rational, by its nature can obey reason,
in which way Aristotle, in the cited place from Book 1 of the Ethics,22 calls the sensitive appetite of man rational by participation, even though it is precisely as such non–rational. And to this order can be reduced an executive potency ad extra23insofar as it is subject to the motion of the will and of the reason, [that is to say, an executive potency] such as a potency to local motion, about which the Philosopher treats in Book 3, Chapters 9 and following, of his De Anima.24
But from that place, especially Texts 4125 and 42,26 there arises a special difficulty. For Aristotle there seems to reject as insufficient this division of potencies into rational and non–rational. A first answer can be that this division can be taken in two ways. First, [it can be taken] as adequate to the potencies of the soul, and in this sense it is not proven by Aristotle in the cited place. In a second way [it can be taken] as a proper and special division of the potencies of a man or of the rational soul. And it is given by Aristotle in this way both here and in Book 1, Chapter 13, of the Eth-ics.27 But the reason for the difference is that the potencies of a man have in some way an order to reason insofar as they all are rooted in the same rational soul. Therefore, they can be appropriately divided in relation to reason, or to the participation or to the lack of an act [of reason?]. But the potencies of brute animals or of other natural things do not have an order to reason. And therefore they are properly called neither rational nor non–rational. But this answer cannot be correctly fitted to this passage of Aristotle, for evidently under non–rational potencies it includes all those which act naturally and without /p. XLVIII/ reason. Hence, he explicitly gives an example of the non–rational potency in heat.28 Again, because through that quasi–privative difference, namely non–rational, there can be included the mode of acting of all natural and vital potencies which do not come up to the level of reason. There does not, therefore, seem to be any doubt that this can be an adequate division of potencies not only in a man, nor only in a soul, but simply in every agent. Therefore, as St.Thomas notes,29 Aristotle, in Book 3 [Chapter 9] of the De Anima, is proceeding not by defining but only by debating. Or at least he disapproves of that division as insufficient, not in an absolute way, but because it was not enough to explain the number and the variety of potencies.
Question 3. The third principal question here is: whether Aristotle has correctly marked the distinction between these potencies from the fact that only rational potencies are principles of contraries?30 About this subject much has been said in Disputation 10 [sic],31 in which we extensively dis-cuss causes, both free and necessitated. And we explain what free potencies are and how they are principles of contrary actions. Again in Disputation
Metaphysics Book IX 169 26, Section 6,32 we treat [the question] whether the same cause can cause contrary effects. And in both places we explain this passage of Aristotle.