We proceed to the fifth article thus:

1. It seems that the things of faith can be known scientifically. [50] We are ignorant of what we do not know scientifically, since ignorance is the opposite of science. But we are not ignorant of the things of faith, since ignorance is unbelief, according to I Tim.1:13: "I did it ignorantly in unbelief." Hence the things of faith can be known scientifically.

2. Again, science is acquired through the giving of reasons. Now the sacred writers give reasons for the things of faith. Hence the things of faith can be known scientifically.

3. Again, whatever is proved by demonstration is known scientifically, since "demonstration is making known by syllogism." Now some of the things of faith are demonstratively proved by the philosophers, for example, that God exists, that he is one, and the like. Hence things of faith can be known scientifically.

4. Again, opinion is farther removed from science than is faith, since faith is said to be a mean between opinion and science. But it is said in 1 Post. An., text ult., that there can, in some way, be opinion and science about the same thing. Hence there can also be faith and science about the same thing.

On the other hand: Gregory says {Hom. in Evang.21): "they do not have faith in things which are seen, but perceive them." Hence they do not perceive things which are of faith. But they do perceive what is known scientifically. There cannot then be faith in what is known scientifically.

I answer: every science depends upon principles which are known in themselves, and which are consequently seen. Everything which is known scientifically, therefore, is in a manner seen. Now we said in the preceding article that it is impossible for the same thing to be both seen and believed by the same person. It is nevertheless possible for the same thing to be seen by one person and believed by another. We hope that we shall some time see what we now believe about the Trinity, in accordance with I Cor.13:12: "now we see through a glass, darkly; but then face to face." But the angels already have this vision. Hence what we believe, they see. It is also possible that what is seen or known scientifically by one man, even while he is a wayfarer, should be believed by another who has no demonstrative knowledge of it. But all men are without scientific knowledge of the things which are proposed for the belief of all alike. Such things are entirely matters of faith. Hence faith and scientific knowledge are not of the same thing.

On the first point: unbelievers are ignorant of the things of faith because they neither see or know them in themselves, nor are aware that they can be believed. Believers do not have demonstrative knowledge of them, yet they know them in so far as the light of faith enables them to see that they are to be believed, as we said in the preceding article.

On the second point: the reasons which are adduced by holy men in order to prove the things of faith are not demonstrative reasons. They are either persuasive, showing that what faith believes is not impossible, or else, as Dionysius says (2 Div. Nom.1, lect.1), they are grounded on principles of the faith itself, such as the authority of sacred Scripture. These principles are sufficient to prove something for believers, just as the principles of natural knowledge prove something for all men. In this way, theology is indeed a science, as we said at the beginning of this work (Pt. I, Q. i, Art.2).

On the third point: things which can be proved by demonstration are included among the things to be believed in faith. This is not because all men believe them purely by faith, but because they are necessary presuppositions to what is believed by faith, and must initially be believed at least by way of faith by those who have no demonstrative knowledge of them.

On the fourth point: as the philosopher says in the same passage: "there can assuredly be scientific knowledge and opinion about the same thing, in different men." This is what we have just said concerning scientific knowledge and faith. But one and the same man can have scientific knowledge and also faith about the same subject in different respects, although not in the same respect. For it is possible to know one thing scientifically, and to hold an opinion about something else, in relation to one and the same thing. Similarly, it is possible to know through demonstration that God is one, and at the same time to believe by faith that he is Triune. But one man cannot have scientific knowledge of the same thing in the same respect, and simultaneously either hold an opinion about it, or believe it by faith -- for different reasons. There cannot be scientific knowledge simultaneously with opinion about the same thing, since it is essential to science that one should be convinced that what is known scientifically cannot possibly be otherwise; whereas it is essential to opinion that one should be aware that its object may be otherwise than it is thought to be. One is equally convinced that what is held in faith cannot possibly be otherwise, owing to the certainty of faith. But the reason why there cannot be scientific knowledge simultaneously with belief about the same thing in the same respect is this -- that to know scientifically is to see, whereas to believe is not to see, as we have already said.

[50] I.e., understood through their cause, so as to be demonstrable.