Objection 1. It would seem that the sensitive and intellectual appetites are not distinct powers. For powers are not differentiated by accidental differences, as we have seen above (Question 77, Article 3). But it is accidental to the appetible object whether it be apprehended by the sense or by the intellect. Therefore the sensitive and intellectual appetites are not distinct powers.
Objection 2. Further, intellectual knowledge is of universals; and so it is distinct from sensitive knowledge, which is of individual things. But there is no place for this distinction in the appetitive part: for since the appetite is a movement of the soul to individual things, seemingly every act of the appetite regards an individual thing. Therefore the intellectual appetite is not distinguished from the sensitive.
Objection 3. Further, as under the apprehensive power, the appetitive is subordinate as a lower power, so also is the motive power. But the motive power which in man follows the intellect is not distinct from the motive power which in animals follows sense. Therefore, for a like reason, neither is there distinction in the appetitive part.
On the contrary, The Philosopher (De Anima iii, 9) distinguishes a double appetite, and says (De Anima iii, 11) that the higher appetite moves the lower.
I answer that, We must needs say that the intellectual appetite is a distinct power from the sensitive appetite. For the appetitive power is a passive power, which is naturally moved by the thing apprehended: wherefore the apprehended appetible is a mover which is not moved, while the appetite is a mover moved, as the Philosopher says in De Anima iii, 10 and Metaph. xii (Did. xi, 7). Now things passive and movable are differentiated according to the distinction of the corresponding active and motive principles; because the motive must be proportionate to the movable, and the active to the passive: indeed, the passive power itself has its very nature from its relation to its active principle. Therefore, since what is apprehended by the intellect and what is apprehended by sense are generically different; consequently, the intellectual appetite is distinct from the sensitive.
Reply to Objection 1. It is not accidental to the thing desired to be apprehended by the sense or the intellect; on the contrary, this belongs to it by its nature; for the appetible does not move the appetite except as it is apprehended. Wherefore differences in the thing apprehended are of themselves differences of the appetible. And so the appetitive powers are distinct according to the distinction of the things apprehended, as their proper objects.
Reply to Objection 2. The intellectual appetite, though it tends to individual things which exist outside the soul, yet tends to them as standing under the universal; as when it desires something because it is good. Wherefore the Philosopher says (Rhetoric. ii, 4) that hatred can regard a universal, as when "we hate every kind of thief." In the same way by the intellectual appetite we may desire the immaterial good, which is not apprehended by sense, such as knowledge, virtue, and suchlike.
Source: Summa Theologica (New Advent)