Objection 1. It would seem that there is a sorrow that is contrary to the pleasure of contemplation. For the Apostle says (2 Corinthians 7:10): "The sorrow that is according to God, worketh penance steadfast unto salvation." Now to look at God belongs to the higher reason, whose act is to give itself to contemplation, according to Augustine (De Trin. xii, 3,4). Therefore there is a sorrow contrary to the pleasure of contemplation.
Objection 2. Further, contrary things have contrary effects. If therefore the contemplation of one contrary gives pleasure, the other contrary will give sorrow: and so there will be a sorrow contrary to the pleasure of contemplation.
Objection 3. Further, as the object of pleasure is good, so the object of sorrow is evil. But contemplation can be an evil: since the Philosopher says (Metaph. xii, 9) that "it is unfitting to think of certain things." Therefore sorrow can be contrary to the pleasure of contemplation.
Objection 4. Further, any work, so far as it is unhindered, can be a cause of pleasure, as stated in Ethic. vii, 12,13; x, 4. But the work of contemplation can be hindered in many ways, either so as to destroy it altogether, or as to make it difficult. Therefore in contemplation there can be a sorrow contrary to the pleasure.
Objection 5. Further, affliction of the flesh is a cause of sorrow. But, as it is written (Ecclesiastes 12:12) "much study is an affliction of the flesh." Therefore contemplation admits of sorrow contrary to its pleasure.
On the contrary, It is written (Wisdom 8:16): "Her," i.e. wisdom's, "conversation hath no bitterness nor her company any tediousness; but joy and gladness." Now the conversation and company of wisdom are found in contemplation. Therefore there is no sorrow contrary to the pleasure of contemplation.
I answer that, The pleasure of contemplation can be understood in two ways. In one way, so that contemplation is the cause, but not the object of pleasure: and then pleasure is taken not in contemplating but in the thing contemplated. Now it is possible to contemplate something harmful and sorrowful, just as to contemplate something suitable and pleasant. Consequently if the pleasure of contemplation be taken in this way, nothing hinders some sorrow being contrary to the pleasure of contemplation.
In another way, the pleasure of contemplation is understood, so that contemplation is its object and cause; as when one takes pleasure in the very act of contemplating. And thus, according to Gregory of Nyssa [Nemesius, De Nat. Hom. xviii.], "no sorrow is contrary to that pleasure which is about contemplation": and the Philosopher says the same (Topic. i, 13; Ethic. x, 3). This, however, is to be understood as being the case properly speaking. The reason is because sorrow is of itself contrary to pleasure in a contrary object: thus pleasure in heat is contrary to sorrow caused by cold. But there is no contrary to the object of contemplation: because contraries, as apprehended by the mind, are not contrary, but one is the means of knowing the other. Wherefore, properly speaking, there cannot be a sorrow contrary to the pleasure of contemplation. Nor has it any sorrow annexed to it, as bodily pleasures have, which are like remedies against certain annoyances; thus a man takes pleasure in drinking through being troubled with thirst, but when the thirst is quite driven out, the pleasure of drinking ceases also. Because the pleasure of contemplation is not caused by one's being quit of an annoyance, but by the fact that contemplation is pleasant in itself: for pleasure is not a "becoming" but a perfect operation, as stated above (Question 31, Article 1).
Accidentally, however, sorrow is mingled with the pleasure of contemplation; and this in two ways: first, on the part of an organ, secondly, through some impediment in the apprehension. On the part of an organ, sorrow or pain is mingled with apprehension, directly, as regards the apprehensive powers of the sensitive part, which have a bodily organ; either from the sensible object disagreeing with the normal condition of the organ, as the taste of something bitter, and the smell of something foul; or from the sensible object, though agreeable, being so continuous in its action on the sense, that it exceeds the normal condition of the organ, as stated above (Question 33, Article 2), the result being that an apprehension which at first was pleasant becomes tedious. But these two things cannot occur directly in the contemplation of the mind; because the mind has no corporeal organ: wherefore it was said in the authority quoted above that intellectual contemplation has neither "bitterness," nor "tediousness." Since, however, the human mind, in contemplation, makes use of the sensitive powers of apprehension, to whose acts weariness is incidental; therefore some affliction or pain is indirectly mingled with contemplation.
Nevertheless, in neither of these ways, is the pain thus accidentally mingled with contemplation, contrary to the pleasure thereof. Because pain caused by a hindrance to contemplation, is not contrary to the pleasure of contemplation, but rather is in affinity and in harmony with it, as is evident from what has been said above (Article 4): while pain or sorrow caused by bodily weariness, does not belong to the same genus, wherefore it is altogether disparate. Accordingly it is evident that no sorrow is contrary to pleasure taken in the very act of contemplation; nor is any sorrow connected with it save accidentally.
Reply to Objection 1. The "sorrow which is according to God," is not caused by the very act of intellectual contemplation, but by something which the mind contemplates: viz. by sin, which the mind considers as contrary to the love of God.
Reply to Objection 2. Things which are contrary according to nature are not contrary according as they exist in the mind: for things that are contrary in reality are not contrary in the order of thought; indeed rather is one contrary the reason for knowing the other. Hence one and the same science considers contraries.
Reply to Objection 3. Contemplation, in itself, is never evil, since it is nothing else than the consideration of truth, which is the good of the intellect: it can, however, be evil accidentally, i.e. in so far as the contemplation of a less noble object hinders the contemplation of a more noble object; or on the part of the object contemplated, to which the appetite is inordinately attached.
Reply to Objection 4. Sorrow caused by a hindrance to contemplation, is not contrary to the pleasure of contemplation, but is in harmony with it, as stated above.
Reply to Objection 5. Affliction of the flesh affects contemplation accidentally and indirectly, as stated above.
Source: Summa Theologica (New Advent)