OK, now I found a place where Aquinas says that the intellect moves the will as the end moves an agent. Very interesting.
Full disclosure: I have not yet read Fr. Keenan’s book. I am just answering according what I know of St. Thomas’ theory of the powers of the soul.
…]Reply to Objection 3: There is no need to go on indefinitely, but we must stop at the intellect as preceding all the rest. For every movement of the will must be preceded by apprehension, whereas every apprehension is not preceded by an act of the will; but the principle of counselling and understanding is an intellectual principle higher than our intellect —namely, God—as also Aristotle says (Eth. Eudemic. vii, 14), and in this way he explains that there is no need to proceed indefinitely.
I love it when St. Thomas agrees with me, heh, heh

. You see, according to Aquinas, there is apprehension (the assumption of concepts—and, although he leaves this implicit—also the making of judgments) before there is volition.
Now, in the body of this article, St Thomas says the intellect moves the will as an end moves an agent and the will moves the intellect as an agent cause…]
Although it is possible that Aquinas changed his mind (there are a number of interesting occasions where he did so), I don’t think there is necessarily a contradiction between this passage—in which the intellect moves the will as an “end” (final cause) moves an agent—and the other one we saw, in which the
object of the will moves the will as a formal cause.
I think what I said earlier still stands: it is not the intellect
as such that usually is the object of the will’s appetite.
But, in essence, I really don’t see why the objects of the will can’t be both final and formal cause in different respects. After all, God is both our Exemplar and our Supreme Good.
They are formal causes inasmuch as they
specify the act of the will (i.e., by choosing
this good, it prevents the will from choosing
that other good); final causes inasmuch as they
inspire desire*, and in this way move the will to act (i.e., to
exercise itself).
This is all fine and I don’t doubt that such is the case at times (at the very least if not always) especially if we take supernatural grace into consideration. As the Church teaches, we can have no good thought or do any good work conducive for salvation without God’s prevenient grace. By grace, God moves both our mind and will. As a side note here, in St Thomas’ treatise on grace, he also calls grace that general help from God by which God is the first mover of our intellects and wills and indeed of all creatures. This general help from God as first mover of all things is distinguished by St Thomas, of course, from supernatural grace.
Yes, but in both cases God is the First Cause, which means that he offers to us the
principles for acting in accord with grace, but He never compels us to act. (That is important, because some interpreters of St. Thomas want to make him a Calvinist…)
Pt. I, Q. 82 was written before Aquinas wrote Pt. I-II where as Fr. Keneen notes, St Thomas makes a shift from the intellect moving the will as an end or final cause moves an agent to the intellect being as a formal cause or principle moving the will as presenting its object to it.
The object specifies the act of the will if the will chooses it so that this specification is as a formal cause since form is what places some thing into a class of things or species. Here it means what kind of act is it, for example, walking, eating, drinking, etc.
Now that I have analyzed both texts, I think I can affirm that the intellect functions as both final and formal cause, in different ways (which echo, actually, the two ways in which the will can be put into act: exercise and specification).
To move on, in Pt. I-II,Q. 17, art. 5, Whether the Act of the Will is Commanded, St Thomas says:
…]
Reply to Objection 3: Since command is an act of reason, that act is commanded which is subject to reason. Now the first act of the will is not due to the direction of the reason but to the instigation of nature, or of a higher cause, as stated above (Question [9], Article [4]). Therefore there is no need to proceed to infinity.
The “command” (
imperium) of reason he is talking about essentially the judgment of the intellect that says, in a moral situation, “you need to do this,” or, “you need to avoid that.” He is basically saying that the “command” of the will (the fact that my will can make the rest of me obey it) is a different animal, so to speak.
Note that the “instigation of nature” refers to the will moving itself. (Remember that throughout Article 9, Thomas is saying that the will can move thanks to two principles: in intrinsic one, and an extrinsic one. The intrinsic one is ultimately the person himself; the extrinsic one is ultimately God.)
In Q. 9, art. 6, St Thomas goes on to say that this external principle or mover of the will is none other than God. …].
Although God is
ultimately the cause of the will’s tendency to the good, that does not prevent created goods from being the
proximate (or secondary) cause of that tendency. This all presupposes that the person
knows about the goods in question and is in a position to desire them.
Note that Aquinas says that we have a natural desire to see God; that is related to God being the ultimate mover of the will. (He can also give more direct motions, like when He gives actual graces.)*