One finds the phrase cognitio fidei in Thomas Aquinas and in such Thomist writers as Josef Pieper. It translates as 'knowledge of faith.' The genitive is to be interpreted subjectively, not objectively: faith is not the object of knowledge; faith is a form or type of knowledge. But how can faith be a type of knowledge? One ought to find this puzzling.
On a standard analysis of 'knows,' where propositional knowledge is at issue, subject S knows that p just in case (i) S believes that p; (ii) S is justified in believing that p; and (iii) p is true. This piece of epistemological boilerplate is the starting point for much of the arcana (Gettier counterexamples, etc.) of contemporary epistemology. But its pedigree is ancient, to be found in Plato's Theaetetus.
It is obvious that on the standard analysis mere belief is inferior to knowledge since if I believe what is false I don't have knowledge, and if I believe what is true without justification I don't have knowledge either. How then can mere belief be a form or type of knowledge? It is rather a necessary but not sufficient condition of knowledge. Or so it seems to the modern mind.
Another puzzle has to do with certainty. Whether or not knowledge entails certainty, it seems to the modern mind that belief definitely does not entail certainty: what I believe but do not know I cannot be certain about since if I believe but do not know, then either truth is lacking or justification is lacking or both. How then can mere belief be said to be certain? And yet we read in Aquinas that "It is part of the concept of belief itself that man is certain of that in which he believes." (Quoted from Pieper, Belief and Faith, p. 15).
It is easy to understand how one who believes but does not know that p can be subjectively certain that p; but it is difficult to understand how such a person can be objectively certain that p. Objective certainty, however, alone has epistemic value.
We now turn to the remarkable Edith Stein (1891-1942), brilliant Jewish student of and assistant to Edmund Husserl, philosopher, Roman Catholic convert, Carmelite nun, victim of the Holocaust at Auschwitz, and saint of the Roman Catholic church. In the 1920s Stein composed an imaginary dialogue between her two philosophical masters, Husserl and Aquinas. Part of what she has them discussing is the nature of faith.
One issue is whether faith gives us access to truth. Stein has Thomas say:
. . . faith is a way to truth. Indeed, in the first place it is a way to truths — plural — which would otherwise be closed to us, and in the second place it is the surest way to truth. For there is no greater certainty than that of faith . . . . (Edith Stein, Knowledge and Faith, tr. Redmond, ICS Publications 2000, pp. 16-17)
Now comes an important question. What is it that we as philosophers want? We want the ultimate truths about the ultimate matters. If so, it is arguable that we should take these truths from whatever source offers them to us even if the source is not narrowly philosophical. We should not say: I will accept only those truths that can be certified by (natural) reason, but rather all truths whether certified by reason or 'certified' by faith. Thus Stein has Aquinas say:
If faith makes accessible truths unattainable by any other means, philosophy, for one thing, cannot forego them without renouncing its universal claim to truth. [. . .] One consequence, then, is a material dependence of philosophy on faith.
Then too, if faith affords the highest certainty attainable by the human mind, and if philosophy claims to bestow the highest certainty, then philosophy must make the certainty of faith its own. It does so first by absorbing the truths of faith, and further by using them as the final criterion by which to gauge all other truths. Hence, a second consequence is a formal dependence of philosophy on faith. (17-18)
But of course this cannot go unchallenged by Husserl. So Stein has him say:
. . . if faith is the final criterion of all other truth, what is the criterion of faith itself? What guarantees that the certainty of my faith is genuine? (20)
Or in terms of of the distinction made above between subjective and objective certainty: what guarantees that the certainty of faith is objective and not merely subjective? The faiths of Jew, Christian, and Muslim are all different. How can the Christian be sure that the revelation he takes on faith has not been superseded by the revelation the Muslim takes on faith? And what about contradictory faith-contents? God cannot be both triune (as the normative Christian believes) and not triune (as the normative Muslim believes). So Christian and Muslim cannot both be objectively certain about their characteristic beliefs; at most they can be subjectively certain. Subjective certainty, however, has no epistemic value.
Stein's Thomas replies to Husserl as follows:
Probably my best answer is that faith is its own guarantee. I could also say that God, who has given us the revelation, vouches for its truth. But this would only be the other side of the same coin. For if we took the two as separate facts, we would fall into a circulus vitiosus [vicious circle], since God is after all what we become certain about in faith. [. . .]
All we can do is point out that for the believer such is the certainty of faith that it relativizes all other certainty, and that he can but give up any supposed knowledge which contradicts his faith. The unique certitude of faith is a gift of grace. It is up to the understanding and will to draw the practical consequences therefrom. Constructing a philosophy on faith belongs to the theoretical consequences. (20-22)
For Thomas and Stein, the certainty of faith is a gift of God. As such, it cannot be merely subjective. It is at once both subjective and objective, subjective as an inner certitude, objective as an effect of divine grace. Husserl, however, will ask how the claim that the certainty of faith is a divine gift can be validated. It is after all, a contestable and contested claim. How does one know that it is true? For Husserl, the claims that God exists and that the Christian revelation is his revelation are but dogmatic presuppositions. They need validation because of the existence of competing claims such as those made by Jews and Muslims and atheists.
If, as Stein says, "faith is its own guarantee," then, since the faith of the Christian and the faith of the Muslim are contradictory with respect to certain key propositions, it follows that one of these faiths offers a false guarantee. You can see from this that the Thomas-Stein stance leaves something to be desired. But Husserl's approach has problems of its own. Closed up within the sphere of his subjectivity, man cannot reach the truly Transcendent, which must irrupt into this sphere and cannot be constituted (Husserl's term) within it. The truly Transcendent is not a transcendence-in-immanence. It cannot be a constituted transcendence.
If man is indeed a creature, there is something absurd about measly man hauling the Creator before the bench of finite reason there to be rudely interrogated about his credentials. On the other hand, the claim that man is a creature is a claim like any other, and man must satisfy his intellectual conscience with respect to this claim. It is precisely his freedom, responsibility and love of truth that drive him to ask: But is it true? And how do we know? And isn't it morally shabby to fool oneself and seek consolation in a fairy tale?
Paradoxically, God creates man in his image and likeness, and thus as free, responsible, and truth-loving; characteristics that then motivate man to put God in the dock.
So there you have it. There are two opposing conceptions of philosophy, one based on the autonomy of reason, the other willing to sacrifice the autonomy of reason for the sake of truths which cannot be certified by reason but which are provided by faith in revelation, a revelation that must simply be accepted in humility and obedience. It looks as if one must simply decide which of these two conceptions to adopt, and that the decision cannot be justified by (natural) reason.
My task, in this and in related posts, is first and foremost to set forth the problems as clearly as I can. Anyone who thinks this problem has an easy solution does not understand it. It is part of the tension between Athens and Jerusalem.