Objection 1. It would seem that faith is not more certain than science and the other intellectual virtues. For doubt is opposed to certitude, wherefore a thing would seem to be the more certain, through being less doubtful, just as a thing is the whiter, the less it has of an admixture of black. Now understanding, science and also wisdom are free of any doubt about their objects; whereas the believer may sometimes suffer a movement of doubt, and doubt about matters of faith. Therefore faith is no more certain than the intellectual virtues.
Objection 2. Further, sight is more certain than hearing. But "faith is through hearing" according to Romans 10:17; whereas understanding, science and wisdom imply some kind of intellectual sight. Therefore science and understanding are more certain than faith.
Further, in matters concerning the intellect, the more perfect is the more certain. Now understanding is more perfect than faith, since faith is the way to understanding, according to another version [the Septuagint] of Isaiah 7:9: "If you will not believe, you shall not understand [Vulgate: 'continue']": and Augustine says (De Trin. xiv, 1) that "faith is strengthened by science." Therefore it seems that science or understanding is more certain than faith.
On the contrary, The Apostle says (1 Thessalonians 2:15): "When you had received of us the word of the hearing," i.e. by faith... "you received it not as the word of men, but, as it is indeed, the word of God." Now nothing is more certain than the word of God. Therefore science is not more certain than faith; nor is anything else.
I answer that, As stated above (I-II, 57, 4, ad 2) two of the intellectual virtues are about contingent matter, viz. prudence and art; to which faith is preferable in point of certitude, by reason of its matter, since it is about eternal things, which never change, whereas the other three intellectual virtues, viz. wisdom, science [In English the corresponding 'gift' is called knowledge] and understanding, are about necessary things, as stated above (I-II, 57, 5, ad 3). But it must be observed that wisdom, science and understanding may be taken in two ways: first, as intellectual virtues, according to the Philosopher (Ethic. vi, 2,3); secondly, for the gifts of the Holy Ghost. If we consider them in the first way, we must note that certitude can be looked at in two ways. First, on the part of its cause, and thus a thing which has a more certain cause, is itself more certain. On this way faith is more certain than those three virtues, because it is founded on the Divine truth, whereas the aforesaid three virtues are based on human reason. Secondly, certitude may be considered on the part of the subject, and thus the more a man's intellect lays hold of a thing, the more certain it is. On this way, faith is less certain, because matters of faith are above the human intellect, whereas the objects of the aforesaid three virtues are not. Since, however, a thing is judged simply with regard to its cause, but relatively, with respect to a disposition on the part of the subject, it follows that faith is more certain simply, while the others are more certain relatively, i.e. for us. Likewise if these three be taken as gifts received in this present life, they are related to faith as to their principle which they presuppose: so that again, in this way, faith is more certain.
Reply to Objection 1. This doubt is not on the side of the cause of faith, but on our side, in so far as we do not fully grasp matters of faith with our intellect.
Reply to Objection 2. Other things being equal sight is more certain than hearing; but if (the authority of) the person from whom we hear greatly surpasses that of the seer's sight, hearing is more certain than sight: thus a man of little science is more certain about what he hears on the authority of an expert in science, than about what is apparent to him according to his own reason: and much more is a man certain about what he hears from God, Who cannot be deceived, than about what he sees with his own reason, which can be mistaken.
Reply to Objection 3. The gifts of understanding and knowledge are more perfect than the knowledge of faith in the point of their greater clearness, but not in regard to more certain adhesion: because the whole certitude of the gifts of understanding and knowledge, arises from the certitude of faith, even as the certitude of the knowledge of conclusions arises from the certitude of premisses. But in so far as science, wisdom and understanding are intellectual virtues, they are based upon the natural light of reason, which falls short of the certitude of God's word, on which faith is founded.
Source: Summa Theologica (New Advent)