in an animal’s body, as in the case of cold or heat; and through the body being affected by the motion of an outward body, the sensitive appetite which is the power of a bodily organ, is also moved indirectly; thus it happens that through some alteration in the body the appetite is roused to the desire of something.  But this is not contrary to the nature of voluntariness, as stated above (ad 1), for such movements caused by an extrinsic principle are of another genus of movement.

Reply Obj. 3:  God moves man to act, not only by proposing the appetible to the senses, or by effecting a change in his body, but also by moving the will itself; because every movement either of the will or of nature, proceeds from God as the First Mover.  And just as it is not incompatible with nature that the natural movement be from God as the First Mover, inasmuch as nature is an instrument of God moving it:  so it is not contrary to the essence of a voluntary act, that it proceed from God, inasmuch as the will is moved by God.  Nevertheless both natural and voluntary movements have this in common, that it is essential that they should proceed from a principle within the agent. ________________________

SECOND ARTICLE [I-II, Q. 6, Art. 2]

Whether There Is Anything Voluntary in Irrational Animals?

Objection 1:  It would seem that there is nothing voluntary in irrational animals.  For a thing is called “voluntary” from voluntas (will).  Now since the will is in the reason (De Anima iii, 9), it cannot be in irrational animals.  Therefore neither is there anything voluntary in them.

Obj. 2:  Further, according as human acts are voluntary, man is said to be master of his actions.  But irrational animals are not masters of their actions; for “they act not; rather are they acted upon,” as Damascene says (De Fide Orth. ii, 27).  Therefore there is no such thing as a voluntary act in irrational animals.

Obj. 3:  Further, Damascene says (De Fide Orth. 24) that “voluntary acts lead to praise and blame.”  But neither praise nor blame is due to the acts of irrational minds.  Therefore such acts are not voluntary.

On the contrary, The Philosopher says (Ethic. iii, 2) that “both children and irrational animals participate in the voluntary.”  The same is said by Damascene (De Fide Orth. 24) and Gregory of Nyssa [Nemesius, De Nat.  Hom. xxxii.].

I answer that, As stated above (A. 1), it is essential to the voluntary act that its principle be within the agent, together with some knowledge of the end.  Now knowledge of the end is twofold; perfect and imperfect.  Perfect knowledge of the end consists in not only apprehending the thing which is the end, but also in knowing it under the aspect of end, and the relationship of the means to that end.  And such knowledge belongs to none but the rational nature.  But imperfect knowledge of the end consists in mere apprehension of the end, without knowing it under the aspect of end, or the relationship of an act to the end.  Such knowledge of the end is exercised by irrational animals, through their senses and their natural estimative power.