Objection 1. It would seem that those things that are of faith can be an object of science. For where science is lacking there is ignorance, since ignorance is the opposite of science. Now we are not in ignorance of those things we have to believe, since ignorance of such things savors of unbelief, according to 1 Timothy 1:13: "I did it ignorantly in unbelief." Therefore things that are of faith can be an object of science.
Objection 2. Further, science is acquired by reasons. Now sacred writers employ reasons to inculcate things that are of faith. Therefore such things can be an object of science.
Objection 3. Further, things which are demonstrated are an object of science, since a "demonstration is a syllogism that produces science." Now certain matters of faith have been demonstrated by the philosophers, such as the Existence and Unity of God, and so forth. Therefore things that are of faith can be an object of science.
Objection 4. Further, opinion is further from science than faith is, since faith is said to stand between opinion and science. Now opinion and science can, in a way, be about the same object, as stated in Poster. i. Therefore faith and science can be about the same object also.
On the contrary, Gregory says (Hom. xxvi in Evang.) that "when a thing is manifest, it is the object, not of faith, but of perception." Therefore things that are of faith are not the object of perception, whereas what is an object of science is the object of perception. Therefore there can be no faith about things which are an object of science.
I answer that, All science is derived from self-evident and therefore "seen" principles; wherefore all objects of science must needs be, in a fashion, seen.
Now as stated above (Article 4), it is impossible that one and the same thing should be believed and seen by the same person. Hence it is equally impossible for one and the same thing to be an object of science and of belief for the same person. It may happen, however, that a thing which is an object of vision or science for one, is believed by another: since we hope to see some day what we now believe about the Trinity, according to 1 Corinthians 13:12: "We see now through a glass in a dark manner; but then face to face": which vision the angels possess already; so that what we believe, they see. On like manner it may happen that what is an object of vision or scientific knowledge for one man, even in the state of a wayfarer, is, for another man, an object of faith, because he does not know it by demonstration.
Nevertheless that which is proposed to be believed equally by all, is equally unknown by all as an object of science: such are the things which are of faith simply. Consequently faith and science are not about the same things.
Reply to Objection 1. Unbelievers are in ignorance of things that are of faith, for neither do they see or know them in themselves, nor do they know them to be credible. The faithful, on the other hand, know them, not as by demonstration, but by the light of faith which makes them see that they ought to believe them, as stated above (4, ad 2,3).
Reply to Objection 2. The reasons employed by holy men to prove things that are of faith, are not demonstrations; they are either persuasive arguments showing that what is proposed to our faith is not impossible, or else they are proofs drawn from the principles of faith, i.e. from the authority of Holy Writ, as Dionysius declares (Div. Nom. ii). Whatever is based on these principles is as well proved in the eyes of the faithful, as a conclusion drawn from self-evident principles is in the eyes of all. Hence again, theology is a science, as we stated at the outset of this work (I, 1, 2).
Reply to Objection 3. Things which can be proved by demonstration are reckoned among the articles of faith, not because they are believed simply by all, but because they are a necessary presupposition to matters of faith, so that those who do not known them by demonstration must know them first of all by faith.
Reply to Objection 4. As the Philosopher says (Poster. i), "science and opinion about the same object can certainly be in different men," as we have stated above about science and faith; yet it is possible for one and the same man to have science and faith about the same thing relatively, i.e. in relation to the object, but not in the same respect. For it is possible for the same person, about one and the same object, to know one thing and to think another: and, in like manner, one may know by demonstration the unity of the Godhead, and, by faith, the Trinity. On the other hand, in one and the same man, about the same object, and in the same respect, science is incompatible with either opinion or faith, yet for different reasons. Because science is incompatible with opinion about the same object simply, for the reason that science demands that its object should be deemed impossible to be otherwise, whereas it is essential to opinion, that its object should be deemed possible to be otherwise. Yet that which is the object of faith, on account of the certainty of faith, is also deemed impossible to be otherwise; and the reason why science and faith cannot be about the same object and in the same respect is because the object of science is something seen whereas the object of faith is the unseen, as stated above.
Source: Summa Theologica (New Advent)