Objection 1. It would seem that consent is directed to the end. Because that on account of which a thing is such is still more such. But it is on account of the end that we consent to the means. Therefore, still more do we consent to the end.
Objection 2. Further, the act of the intemperate man is his end, just as the act of the virtuous man is his end. But the intemperate man consents to his own act. Therefore consent can be directed to the end.
Objection 3. Further, desire of the means is choice, as stated above (Question 13, Article 01). If therefore consent were only directed to the means it would nowise differ from choice. And this is proved to be false by the authority of Damascene who says (De Fide Orth. ii, 22) that "after the approval" which he calls "the sentence," "comes the choice." Therefore consent is not only directed to the means.
On the contrary, Damascene says (De Fide Orth. ii, 22) that the "sentence," i.e. the consent, takes place "when a man approves and embraces the judgment of his counsel." But counsel is only about the means. Therefore the same applies to consent.
I answer that, Consent is the application of the appetitive movement to something that is already in the power of him who causes the application. Now the order of action is this: First there is the apprehension of the end; then the desire of the end; then the counsel about the means; then the desire of the means. Now the appetite tends to the last end naturally: wherefore the application of the appetitive movement to the apprehended end has not the nature of consent, but of simple volition. But as to those things which come under consideration after the last end, in so far as they are directed to the end, they come under counsel: and so counsel can be applied to them, in so far as the appetitive movement is applied to the judgment resulting from counsel. But the appetitive movement to the end is not applied to counsel: rather is counsel applied to it, because counsel presupposes the desire of the end. On the other hand, the desire of the means presupposes the decision of counsel. And therefore the application of the appetitive movement to counsel's decision is consent, properly speaking. Consequently, since counsel is only about the means, consent, properly speaking, is of nothing else but the means.
Reply to Objection 1. Just as the knowledge of conclusions through the principles is science, whereas the knowledge of the principles is not science, but something higher, namely, understanding; so do we consent to the means on account of the end, in respect of which our act is not consent but something greater, namely, volition.
Reply to Objection 2. Delight in his act, rather than the act itself, is the end of the intemperate man, and for sake of this delight he consents to that act.
Reply to Objection 3. Choice includes something that consent has not, namely, a certain relation to something to which something else is preferred: and therefore after consent there still remains a choice. For it may happen that by aid of counsel several means have been found conducive to the end, and through each of these meeting with approval, consent has been given to each: but after approving of many, we have given our preference to one by choosing it. But if only one meets with approval, then consent and choice do not differ in reality, but only in our way of looking at them; so that we call it consent, according as we approve of doing that thing; but choice according as we prefer it to those that do not meet with our approval.
Source: Summa Theologica (New Advent)