Alain de Libera, who previously published a French translation of Aquinas’ On the Unity of the Intellect with extensive notes and commentary, opts in his Archaeology of the Subject to focus on the much shorter treatment of Averroes by Aquinas in Question 76 of the first part of Summa Theologica. In the current context, de Libera is most interested in developments on a time scale of centuries, and the latter text was far better known in later times.
In this Question, after briefly summarizing the argument from On the Unity of the Intellect that Averroes makes the human something thought rather than a thinker, Aquinas makes a more abstract claim that Averroes confuses immanent and transitive action.
De Libera appears to be setting the stage for an “archaeological” inquiry into the notion of immanent and transitive action, which he says originated in anti-Averroist arguments but came to have much more general purport.
According to de Libera, Aquinas claims Aristotle’s authority for the thesis that “thought is an immanent action” (Archéologie du sujet volume 3 part 1, p. 301). Implicitly, Aquinas would have meant that thought must be an action immanent in the soul, since the whole dispute with Averroes was about the way in which thought is said to be “in” the soul.
In support, de Libera cites (p. 301 note 1) a passage from book IX of the Metaphysics, for which I’ll substitute Joe Sachs’ translation: “of those things which have no other work besides their being-at-work, the being-at-work of them is present in themselves (as seeing is in the one seeing and contemplation in the one contemplating, and life is in the soul, and hence happiness too, since it is a sort of life). And so it is clear that thinghood and form are being-at-work” (Sachs trans., p. 179; I’ve been using the more conventional “actuality” rather than Sachs’ arguably better “being-at-work” for energeia).
This was part of Aristotle’s larger argument that “the end is work, and the work is a being-at-work, and this is why the phrase being-at work is meant by reference to work and extends to being-at-work-staying-complete [entelecheia]” (ibid). Sachs comments in a note, “That is, beings do not just happen to perform strings of isolated deeds, but their activity forms a continuous state of being-at-work, in which they achieve the completion that makes them what they are. Aristotle is arguing that the very thinghood [ousia or substance] of a thing is not what might be hidden inside it, but a definite way of being unceasingly at-work, that makes it a thing at all and the kind of thing it is” (ibid).
I would note first of all that thought is not mentioned in the passage from Aristotle. Contemplation is, but Aristotle in his carefully minimalist way just says contemplation is in “the one contemplating”. What he chooses to explicitly say is “in the soul” in this way is the being-at-work of life.
Secondly, there is a big difference between the “action” Aquinas speaks of and “being-at-work” in Aristotle. Action seems to be considered in the first instance as something punctual and immediate, whereas Aristotle emphasizes extended processes like building a house, and seems to think there is something essential about their extendedness.
Third, de Libera makes it clear that Aquinas thinks of action principally in terms of efficient causation, whereas Aristotle emphasizes the relation of being-at-work to ends.
Fourth, like many later authors, Aquinas seems to have a contracted view of what an efficient cause is. Aristotle says that the art of building is more properly an efficient cause of a house than the carpenter, the carpenter’s hammer, or the hammer’s blow. Aquinas’ example is that of a bailiff acting on behalf of a king. This does capture the sense in which an efficient cause is a means by which an end is accomplished, but I think it is not accidental that Aquinas’ example involves exercising power and emphasizes simple “doing”, whereas Aristotle’s example explicitly foregrounds the way of doing over the more primitive fact that there is a doing. (See also Not Power and Action; Aquinas and Scotus on Power.)
Update: There is always a bit of risk with interim reports. Now that I’ve read a bit further, it appears that the actual argument of Aquinas is that thought is intrinsically an immanent action, independent of the dispute about whether or not the soul its “subject”. The use of this against Averroes was actually hypothetical — if, as Averroes says, thought has its proper “subject” in a separate material intellect, then, Aquinas says, thought would have to be immanent to the material intellect, and as a result we could not legitimately attribute it to the human thinker. This does not affect the four concerns I expressed above, but it illustrates the subtlety and sophistication of Aquinas’ argumentation. (See also A Thomistic Grammar of Action; Roots of Action; Act and Action).