Reply Obj. 2: It is proper to an instrument to be moved by the principal agent, yet diversely, according to the property of its nature. For an inanimate instrument, as an axe or a saw, is moved by the craftsman with only a corporeal movement; but an instrument animated by a sensitive soul is moved by the sensitive appetite, as a horse by its rider; and an instrument animated with a rational soul is moved by its will, as by the command of his lord the servant is moved to act, the servant being like an animate instrument, as the Philosopher says (Polit. i, 2, 4; Ethic. viii, 11). And hence it was in this manner that the human nature of Christ was the instrument of the Godhead, and was moved by its own will.
Reply Obj. 3: The power of the will is natural, and necessarily follows upon the nature; but the movement or act of this power—which is also called will—is sometimes natural and necessary, e.g. with respect to beatitude; and sometimes springs from free-will and is neither necessary nor natural, as is plain from what has been stated in the Second Part (I-II, Q. 10, AA. 1, 2) [*Cf. I, Q. 82, A. 2]. And yet even reason itself, which is the principle of this movement, is natural. Hence besides the Divine will it is necessary to place in Christ a human will, not merely as a natural power, or a natural movement, but even as a rational movement.
Reply Obj. 4: When we say "to will in a certain way," we signify a determinate mode of willing. Now a determinate mode regards the thing of which it is the mode. Hence since the will pertains to the nature, "to will in a certain way" belongs to the nature, not indeed considered absolutely, but as it is in the hypostasis. Hence the human will of Christ had a determinate mode from the fact of being in a Divine hypostasis, i.e. it was always moved in accordance with the bidding of the Divine will. _______________________
SECOND ARTICLE [III, Q. 18, Art. 2]
Whether in Christ There Was a Will of Sensuality Besides the Will of
Reason?
Objection 1: It would seem that in Christ there was no will of sensuality besides the will of reason. For the Philosopher says (De Anima iii, text. 42) that "the will is in the reason, and in the sensitive appetite are the irascible and concupiscible parts." Now sensuality signifies the sensitive appetite. Hence in Christ there was no will of sensuality.
Obj. 2: Further, according to Augustine (De Trin. xii, 12, 13) the sensuality is signified by the serpent. But there was nothing serpent-like in Christ; for He had the likeness of a venomous animal without the venom, as Augustine says (De Pecc. Merit. et Remiss. i, 32). Hence in Christ there was no will of sensuality.
Obj. 3: Further, will is consequent upon nature, as was said (A. 1).
But in Christ there was only one nature besides the Divine. Hence in
Christ there was only one human will.
On the contrary, Ambrose says (De Fide ii, 7): "Mine is the will which He calls His own; because as Man He assumed my sorrow." From this we are given to understand that sorrow pertains to the human will of Christ. Now sorrow pertains to the sensuality, as was said in the Second Part (I-II, Q. 23, A. 1; Q. 25, A. 1). Therefore, seemingly, in Christ there is a will of sensuality besides the will of reason.
I answer that, As was said (Q. 9, A. 1), the Son of God assumed human nature together with everything pertaining to the perfection of human nature. Now in human nature is included animal nature, as the genus in its species. Hence the Son of God must have assumed together with the human nature whatever belongs to animal nature; one of which things is the sensitive appetite, which is called the sensuality. Consequently it must be allowed that in Christ there was a sensual appetite, or sensuality. But it must be borne in mind that sensuality or the sensual appetite, inasmuch as it naturally obeys reason, is said to be "rational by participation," as is clear from the Philosopher (Ethic. i, 13). And because "the will is in the reason," as stated above, it may equally be said that the sensuality is "a will by participation."