Reply Obj. 1: This argument is based on the will, essentially so called, which is only in the intellectual part; but the will by participation can be in the sensitive part, inasmuch as it obeys reason.
Reply Obj. 2: The sensuality is signified by the serpent—not as regards the nature of the sensuality, which Christ assumed, but as regards the corruption of the fomes, which was not in Christ.
Reply Obj. 3: "Where there is one thing on account of another, there seems to be only one" (Aristotle, Topic. iii); thus a surface which is visible by color is one visible thing with the color. So, too, because the sensuality is called the will, only because it partakes of the rational will, there is said to be but one human will in Christ, even as there is but one human nature. _______________________
THIRD ARTICLE [III, Q. 18, Art. 3]
Whether in Christ There Were Two Wills As Regards the Reason?
Objection 1: It would seem that in Christ there were two wills as regards the reason. For Damascene says (De Fide Orth. ii, 22) that there is a double will in man, viz. the natural will which is called thelesis, and the rational will which is called boulesis. Now Christ in His human nature had whatever belongs to the perfection of human nature. Hence both the foregoing wills were in Christ.
Obj. 2: Further, the appetitive power is diversified in man by the difference of the apprehensive power, and hence according to the difference of sense and intellect is the difference of sensitive and intellective appetite in man. But in the same way as regards man's apprehension, we hold the difference of reason and intellect; both of which were in Christ. Therefore there was a double will in Him, one intellectual and the other rational.
Obj. 3: Further, some [*Hugh of St. Victor, De Quat. Volunt. Christ.] ascribe to Christ "a will of piety," which can only be on the part of reason. Therefore in Christ on the part of reason there are several wills.
On the contrary, In every order there is one first mover. But the will is the first mover in the genus of human acts. Therefore in one man there is only one will, properly speaking, which is the will of reason. But Christ is one man. Therefore in Christ there is only one human will.
I answer that, As stated above (A. 1, ad 3), the will is sometimes taken for the power, and sometimes for the act. Hence if the will is taken for the act, it is necessary to place two wills, i.e. two species of acts of the will in Christ on the part of the reason. For the will, as was said in the I-II, Q. 8, AA. 2, 3, regards both the end and the means; and is affected differently towards both. For towards the end it is borne simply and absolutely, as towards what is good in itself; but towards the means it is borne under a certain relation, as the goodness of the means depends on something else. Hence the act of the will, inasmuch as it is drawn to anything desired of itself, as health, which act is called by Damascene thelesis—i.e. simple will, and by the masters "will as nature," is different from the act of the will as it is drawn to anything that is desired only in order to something else, as to take medicine; and this act of the will Damascene calls boulesis—i.e. counseling will, and the masters, "will as reason." But this diversity of acts does not diversify the power, since both acts regard the one common ratio of the object, which is goodness. Hence we must say that if we are speaking of the power of the will, in Christ there is but one human will, essentially so called and not by participation; but if we are speaking of the will as an act, we thus distinguish in Christ a will as nature, which is called thelesis, and a will as reason, which is called boulesis.