Objection 1. It would seem that the contemplative life has nothing to do with the affections and pertains wholly to the intellect. For the Philosopher says (Metaph. ii, text. 3 [Ed Did. ia, 1) that "the end of contemplation is truth." Now truth pertains wholly to the intellect. Therefore it would seem that the contemplative life wholly regards the intellect.
Objection 2. Further, Gregory says (Moral. vi, 37; Hom. xix in Ezech.) that "Rachel, which is interpreted 'vision of the principle' [Or rather, 'One seeing the principle,' if derived from rah and irzn; Cf. Jerome, De Nom. Hebr.], signifies the contemplative life." Now the vision of a principle belongs properly to the intellect. Therefore the contemplative life belongs properly to the intellect.
Objection 3. Further, Gregory says (Hom. xiv in Ezech.) that it belongs to the contemplative life, "to rest from external action." Now the affective or appetitive power inclines to external actions. Therefore it would seem that the contemplative life has nothing to do with the appetitive power.
On the contrary, Gregory says (Hom. xiv in Ezech.) that "the contemplative life is to cling with our whole mind to the love of God and our neighbor, and to desire nothing beside our Creator." Now desire and love pertain to the affective or appetitive power, as stated above (I-II, 25, 2; I-II, 26, 2). Therefore the contemplative life has also something to do with the affective or appetitive power.
I answer that, As stated above (Question 179, Article 1) theirs is said to be the contemplative who are chiefly intent on the contemplation of truth. Now intention is an act of the will, as stated above (I-II, 12, 1), because intention is of the end which is the object of the will. Consequently the contemplative life, as regards the essence of the action, pertains to the intellect, but as regards the motive cause of the exercise of that action it belongs to the will, which moves all the other powers, even the intellect, to their actions, as stated above (I, 82, 4; I-II, 09, 1).
Now the appetitive power moves one to observe things either with the senses or with the intellect, sometimes for love of the thing seen because, as it is written (Matthew 6:21), "where thy treasure is, there is thy heart also," sometimes for love of the very knowledge that one acquires by observation. Wherefore Gregory makes the contemplative life to consist in the "love of God," inasmuch as through loving God we are aflame to gaze on His beauty. And since everyone delights when he obtains what he loves, it follows that the contemplative life terminates in delight, which is seated in the affective power, the result being that love also becomes more intense.
Reply to Objection 1. From the very fact that truth is the end of contemplation, it has the aspect of an appetible good, both lovable and delightful, and in this respect it pertains to the appetitive power.
Reply to Objection 2. We are urged to the vision of the first principle, namely God, by the love thereof; wherefore Gregory says (Hom. xiv in Ezech.) that "the contemplative life tramples on all cares and longs to see the face of its Creator."
Reply to Objection 3. The appetitive power moves not only the bodily members to perform external actions, but also the intellect to practice the act of contemplation, as stated above.
Source: Summa Theologica (New Advent)