Reply Obj. 2: As in the apprehensive powers of the sensitive part there is an estimative power, which perceives those things which do not impress the senses, as we have said above (Q. 78, A. 2); so also in the sensitive appetite there is a certain appetitive power which regards something as suitable, not because it pleases the senses, but because it is useful to the animal for self-defense: and this is the irascible power.
Reply Obj. 3: Hatred belongs simply to the concupiscible appetite: but by reason of the strife which arises from hatred, it may belong to the irascible appetite. _______________________
THIRD ARTICLE [I, Q. 81, Art. 3]
Whether the irascible and concupiscible appetites obey reason?
Objection 1: It would seem that the irascible and concupiscible appetites do not obey reason. For irascible and concupiscible are parts of sensuality. But sensuality does not obey reason, wherefore it is signified by the serpent, as Augustine says (De Trin. xii, 12,13). Therefore the irascible and concupiscible appetites do not obey reason.
Obj. 2: Further, what obeys a certain thing does not resist it. But the irascible and concupiscible appetites resist reason: according to the Apostle (Rom. 7:23): "I see another law in my members fighting against the law of my mind." Therefore the irascible and concupiscible appetites do not obey reason.
Obj. 3: Further, as the appetitive power is inferior to the rational part of the soul, so also is the sensitive power. But the sensitive part of the soul does not obey reason: for we neither hear nor see just when we wish. Therefore, in like manner, neither do the powers of the sensitive appetite, the irascible and concupiscible, obey reason.
On the contrary, Damascene says (De Fide Orth. ii, 12) that "the part of the soul which is obedient and amenable to reason is divided into concupiscence and anger."
I answer that, In two ways the irascible and concupiscible powers obey the higher part, in which are the intellect or reason, and the will; first, as to reason, secondly as to the will. They obey the reason in their own acts, because in other animals the sensitive appetite is naturally moved by the estimative power; for instance, a sheep, esteeming the wolf as an enemy, is afraid. In man the estimative power, as we have said above (Q. 78, A. 4), is replaced by the cogitative power, which is called by some "the particular reason," because it compares individual intentions. Wherefore in man the sensitive appetite is naturally moved by this particular reason. But this same particular reason is naturally guided and moved according to the universal reason: wherefore in syllogistic matters particular conclusions are drawn from universal propositions. Therefore it is clear that the universal reason directs the sensitive appetite, which is divided into concupiscible and irascible; and this appetite obeys it. But because to draw particular conclusions from universal principles is not the work of the intellect, as such, but of the reason: hence it is that the irascible and concupiscible are said to obey the reason rather than to obey the intellect. Anyone can experience this in himself: for by applying certain universal considerations, anger or fear or the like may be modified or excited.
To the will also is the sensitive appetite subject in execution, which is accomplished by the motive power. For in other animals movement follows at once the concupiscible and irascible appetites: for instance, the sheep, fearing the wolf, flees at once, because it has no superior counteracting appetite. On the contrary, man is not moved at once, according to the irascible and concupiscible appetites: but he awaits the command of the will, which is the superior appetite. For wherever there is order among a number of motive powers, the second only moves by virtue of the first: wherefore the lower appetite is not sufficient to cause movement, unless the higher appetite consents. And this is what the Philosopher says (De Anima iii, 11), that "the higher appetite moves the lower appetite, as the higher sphere moves the lower." In this way, therefore, the irascible and concupiscible are subject to reason.