Of the Power of Sensuality

I answer that, The name sensuality seems to be taken from the sensual movement, of which Augustine speaks (De Trin. xii, 12, 13), just as the name of a power is taken from its act; for instance, sight from seeing. Now the sensual movement is an appetite following sensitive apprehension. For the act of the apprehensive power is not so properly called a movement as the act of the appetite: since the operation of the apprehensive power is completed in the very fact that the thing apprehended is in the one that apprehends: while the operation of the appetitive power is completed in the fact that he who desires is borne towards the thing desirable. Therefore the operation of the apprehensive power is likened to rest: whereas the operation of the appetitive power is rather likened to movement. Wherefore by sensual movement we understand the operation of the appetitive power: so that sensuality is the name of the sensitive appetite.

I answer that, The sensitive appetite is one generic power, and is called sensuality; but it is divided into two powers, which are species of the sensitive appetite—the irascible and the concupiscible. In order to make this clear, we must observe that in natural corruptible things there is needed an inclination not only to the acquisition of what is suitable and to the avoiding of what is harmful, but also to resistance against corruptive and contrary agencies which are a hindrance to the acquisition of what is suitable, and are productive of harm. For example, fire has a natural inclination, not only to rise from a lower position, which is unsuitable to it, towards a higher position which is suitable, but also to resist whatever destroys or hinders its action. Therefore, since the sensitive appetite is an inclination following sensitive apprehension, as natural appetite is an inclination following the natural form, there must needs be in the sensitive part two appetitive powers—one through which the soul is simply inclined to seek what is suitable, according to the senses, and to fly from what is hurtful, and this is called the concupiscible: and another, whereby an animal resists these attacks that hinder what is suitable, and inflict harm, and this is called the irascible. Whence we say that its object is something arduous, because its tendency is to overcome and rise above obstacles. Now these two are not to be reduced to one principle: for sometimes the soul busies itself with unpleasant things, against the inclination of the concupiscible appetite, in order that, following the impulse of the irascible appetite, it may fight against obstacles. Wherefore also the passions of the irascible appetite counteract the passions of the concupiscible appetite: since the concupiscence, on being aroused, diminishes anger; and anger being roused, diminishes concupiscence in many cases. This is clear also from the fact that the irascible is, as it were, the champion and defender of the concupiscible when it rises up against what hinders the acquisition of the suitable things which the concupiscible desires, or against what inflicts harm, from which the concupiscible flies. And for this reason all the passions of the irascible appetite rise from the passions of the concupiscible appetite and terminate in them; for instance, anger rises from sadness, and having wrought vengeance, terminates in joy. For this reason also the quarrels of animals are about things concupiscible—namely, food and sex, as the Philosopher says [De Animal. Histor. viii.].

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.