To the third one proceeds thus. It seems that habitude does not involve order to act. For anything acts according as it is actual. But the Philosopher says, in De Anima III, that when someone becomes knowing according to habitude, then he is so still potentially, but in another way than before learning. Therefore 'habitude' does not involve habitude as principle to act.
Further, what is put in the definition of something, pertains to it per se. But to be a principle of action is put in the definition of power, as is clear in Metaphys. V. Therefore to be principle of act is appropriate per se to power. But what is per se is first in any genus. If therefore habitude is also principle of act, it is posterior to power. And so habitude or disposition will not be the first species of quality.
Further, health is sometimes habitude, and likewise slimness and beauty. But these are not said through order to act. Therefore it does not belong to the notion of habitude that it be principle of act.
But contrariwise is what Augustine says, in the book on the good of marriage, that habitude is that by which something is enacted when there is need. And the Commentator says, on De Anima III, that habitude is that by which one enacts something when one wills.
I reply that it must be said that order to act can converge [competere] with habitude both according to the notion of habitude and according to the notion of the subject in which it is a habitude. Indeed, according to the notion of habitude, it is appropriate for every habitude to have, in some way, order to act. For it is in the notion of habitude that it involves a certain habitude ordered to the nature of the thing according to what is appropriate or inappropriate. But the nature of the thing, which is the end of generation, is further ordered to another end, which is either working or some work to which one comes by working. Thus habitude not only involves order to the very nature of the thing, but also consequently to working inasmuch as it is an end of nature, or leading to the end. And thus in Metaphys. V it is said in the definition of habitude that it is disposition according to which the disposed is disposed well or badly, either according to itself, that is, according to its nature, or to another, that is, in order to an end.
But there are certain habitudes that also, first and principally, involve order to act on the part of the subject in which they are, because, as was said, habitude involves, first and per se, habitude to the nature of the thing. If, therefore, the nature of the thing in which it is a habitude consists in some order to act, it follows that the habitude principally involves order to act. And it is clear that the nature and notion of power is to be principle of act; thus every habitude that has some power as its subject principally involves some order to act.
Therefore to the first it must be said that habitude is a sort of act inasmuch as it is quality, and accordingly can be a principle of working, but it is potential with respect to working. Thus habitude is called first act and working second act, as is clear in De Anima II.
To the second it must be said that it is not in the notion of habitude that it is related to power, but that it is related to nature. And because nature precedes action, to which power is related, habitude is placed as a species of quality before power.
To the third it must be said that health is called a habitude or habitual disposition in order to nature, as was said. However, inasmuch as nature is a principle of act, it consequently involves order to act. Thus the Philosopher says in De Historia Animal. X that man, or some member, is called healthy when it can do the work of someone healthy. And likewise for the others.
[Thomas Aquinas, ST 2-1.49.3, my translation. The Latin is here, the Dominican Fathers translation is here.]
This article may seem somewhat dry and abstract, but it is the root of some puzzles in the Thomistic account of habitude.
The lesser puzzle is how and in what way health and beauty are habitudes. For Aristotle, health and beauty are paradigmatically habitudes; he constantly goes to them for examples. Aquinas in a number of places seems to accept this, but he also in a number of places pulls back from it, and this particular article's conclusion, that habitude involves ordering to act, seems to be one of the reasons. How health and beauty are active in this way is not immediately obvious. The key seems to be the point that Aquinas makes to the third objection, that health is a "habitude or habitual disposition" to the extent and in the way that it is concerned with healthy operation. Merely to be healthy by happenstance is not a habitude; it is health-as-habitude is when you as-if-naturally carry yourself and behave in ways that are healthy ways of acting. Many people at any given moment happen to be healthy, but we can recognize that some people live in something like an anti-hypochondriac way; health for them is an active possession, as their attitudes, the actions and appetites to which they tend, their responses to things, all tend toward health. They are healthy-livers, not in the sense that they pursue health fads or the like, but in the sense that health is not just something that they happen to have but an expression of their way of living. Something similar can be said of beauty; some people happen to be beautiful because of youth or a chance combination of factors, but some people are beautiful in a way that expresses their life -- part of their beauty is how they carry themselves, the kinds of behaviors they tend to toward, and the like. They make themselves beautiful, but it's not as if they are trying to force it; making themselves beautiful is just what they have come to tend to do, so that it's part of what living is for them.
A more complicated puzzle is the relation between habitude and will. This requires some further pieces in place, so can't but fully handled here, but this article plays a role in the puzzle, so it's necessary to say a few things here before the knot becomes too tangled. A later objection will refer back to this habitude in terms that seem to suggest that this article should be read as establishing that will is essential to habitude, and Aquinas doesn't seem to deny it. This would complicate the health and beauty examples even further, and would constitute a massive change from Aristotle, who (first) does not have an account of will at all, despite saying things relevant to willing, and (second) pretty clearly holds that developing habitudes is something found across the animal world, and, indeed, given what Aristotle says about habitude, it would make sense for him to extend it to plants, as well. Unlike a number of commentators, I don't think we are actually committed by the evidence to Aquinas deviating so completely from Aristotle, but obviously how this article is interpreted is of some relevance to this.
Notably, the only place in the article in which 'will' even shows up explicitly is in the sed contra, with the reference to Averroes (the Commentator). The reference here is a summary paraphrase, not a translation. Aquinas, in Summa Contra Gentiles 2.78.6 (on the agent intellect), gives a more direct translation:
“For the essence of habit,” as the Commentator, Averroes, says on this very text, “consists in this, that its possessor understands by means of that which is proper to him -- understands by himself and whenever he wills, with no need of anything extrinsic”; since Averroes explicitly likens to a habit, not the effect itself, but “the intellect by which we make all things.”
Thus the summary paraphrase is generalizing from Averroes's original point, which is specifically about the intellect understanding. Voluerit occurs in both the original and the summary paraphrase, but it seems clear that generalizing affects how we have to understand it -- it, too, needs to be generalized, and therefore we seem to have to allow that it may be used metaphorically or merely representatively here.
