St. Thomas Aquinas on Faith and Evidentialism

Often secularists make the accusation that faith is "believing without evidence." This statement needs clarification: we believe without evidence that falls under science popularly understood, i.e. empirically-testable evidence, but we do not believe without evidence. Evidence here basically means epistemic justification or warrant. St. Thomas argues that faith gives us the greatest warrant for any belief because its warrant is the authority of God, or Truth itself, which can neither deceive nor be deceived.

But we have to remember the proper content of faith: faith is not in the existence of God but in what God has told us about Himself, namely, the realities contained within the Creed. If a secularist, thinking that faith means believing in the existence of God, accuses us of circular reasoning, then he is right, for we would be arguing that we believe in God because God is the best authority. But if the secularist understands faith as we understand it, namely, believing what God has told us about Himself--already presupposing that we believe that God exists, which is a matter of reason, not faith--, then there is no circular argument but an appeal to the proper, and in fact, most proper, authority, God Himself.

But St. Thomas gives a twist: he doesn't think that we actually lack empirical evidence for faith (but this evidence cannot be evidence in the strict sense but only analogously so).

“The Evidence of Things that Appear Not.”—But someone will say that it is foolish to believe what is not seen, and that one should not believe in things that he cannot see. I answer by saying that the imperfect nature of our intellect takes away the basis of this difficulty. For if man of himself could in a perfect manner know all things visible and invisible, it would indeed be foolish to believe what he does not see. But our manner of knowing is so weak that no philosopher could perfectly investigate the nature of even one little fly. We even read that a certain philosopher spent thirty years in solitude in order to know the nature of the bee. If, therefore, our intellect is so weak, it is foolish to be willing to believe concerning God only that which man can know by himself alone. And against this is the word of Job: “Behold, God is great, exceeding our knowledge” [Job 36:26]. One can also answer this question by supposing that a certain master had said something concerning his own special branch of knowledge, and some uneducated person would contradict him for no other reason than that he could not understand what the master said! Such a person would be considered very foolish. So, the intellect of the Angels as greatly exceeds the intellect of the greatest philosopher as much as that of the greatest philosopher exceeds the intellect of the uneducated man. Therefore, the philosopher is foolish if he refuses to believe what an Angel says, and far greater fool to refuse to believe what God says. Against such are these words: “For many things are shown to you above the understanding of men” [Sir 3:25]. 

Then, again, if one were willing to believe only those things which one knows with certitude, one could not live in this world. How could one live unless one believed others? How could one know that this man is one’s own father? Therefore, it is necessary that one believe others in matters which one cannot know perfectly for oneself. But no one is so worthy of belief as is God, and hence they who do not believe the words of faith are not wise, but foolish and proud. As the Apostle says: “He is proud, knowing nothing” [1 Tim 6:4]. And also: “I know whom I have believed; and I am certain” [2 Tim 1:12]. And it is written: “You who fear the Lord, believe Him and your reward shall not be made void” [Sir 2:8]. Finally, one can say also that God proves the truth of the things which faith teaches. Thus, if a king sends letters signed with his seal, no one would dare to say that those letters did not represent the will of the king. In like manner, everything that the Saints believed and handed down to us concerning the faith of Christ is signed with the seal of God. This seal consists of those works which no mere creature could accomplish; they are the miracles by which Christ confirmed the sayings of the apostles and of the Saints. 

If, however, you would say that no one has witnessed these miracles, I would reply in this manner. It is a fact that the entire world worshipped idols and that the faith of Christ was persecuted, as the histories of the pagans also testify. But now all are turned to Christ—wise men and noble and rich—converted by the words of the poor and simple preachers of Christ. Now, this fact was either miracle or it was not. If it is miraculous, you have what you asked for, a visible fact; if it is not, then there could not be a greater miracle than that the whole world should have been converted without miracles. And we need go no further. We are more certain, therefore, in believing the things of faith than those things which can be seen, because God’s knowledge never deceives us, but the visible sense of man is often in error.

Source: St. Thomas Aquinas, Commentary on the Apostles' Creed, trans. Joseph B. Collins, prologue; http://dhspriory.org/thomas/english/Creed.htm