Objection 1. It would seem that sensuality is not only appetitive, but also cognitive. For Augustine says (De Trin. xii, 12) that "the sensual movement of the soul which is directed to the bodily senses is common to us and beasts." But the bodily senses belong to the apprehensive powers. Therefore sensuality is a cognitive power.
Objection 2. Further, things which come under one division seem to be of one genus. But Augustine (De Trin. xii, 12) divides sensuality against the higher and lower reason, which belong to knowledge. Therefore sensuality also is apprehensive.
Objection 3. Further, in man's temptations sensuality stands in the place of the "serpent." But in the temptation of our first parents, the serpent presented himself as one giving information and proposing sin, which belong to the cognitive power. Therefore sensuality is a cognitive power.
On the contrary, Sensuality is defined as "the appetite of things belonging to the body."
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.
Reply to Objection 1. By saying that the sensual movement of the soul is directed to the bodily senses, Augustine does not give us to understand that the bodily senses are included in sensuality, but rather that the movement of sensuality is a certain inclination to the bodily senses, since we desire things which are apprehended through the bodily senses. And thus the bodily senses appertain to sensuality as a preamble.
Reply to Objection 2. Sensuality is divided against higher and lower reason, as having in common with them the act of movement: for the apprehensive power, to which belong the higher and lower reason, is a motive power; as is appetite, to which appertains sensuality.
Reply to Objection 3. The serpent not only showed and proposed sin, but also incited to the commission of sin. And in this, sensuality is signified by the serpent.
Source: Summa Theologica (New Advent)