158. Having demonstrated the possibility, indeed the moral necessity, of divine revelation, we must now inquire whether and how it can be known that divine origin belongs to some doctrine, or that some religion is truly divinely revealed. But when we inquire into the mode by which the existence of divine revelation can be established for us, by that very fact we investigate the means through which we can arrive at knowledge of this sort. These means are usually called the notes of revelation, since they manifest divine revelation itself; they are also called criteria of revelation, insofar as from them true revelation is judged and discerned; or they are also called motives of credibility, because by their help the fact of revelation is rendered evidently credible, and therefore it becomes known with certainty that the revealed truths themselves must be admitted altogether.
159. The necessity of knowing, and indeed with certainty, the fact of revelation is easily understood by all. For if God reveals anything, firm faith must be given to Him, as we showed in the treatise On the Virtues (n. 1029 ff.). But something would be believed irrationally with firm and irreformable assent as divinely revealed if there were some doubt about revelation itself. Therefore it is necessary that revelation itself be established with certainty. Hence among the propositions condemned by Innocent XI is the twenty-fifth, which sounds thus: “The assent of supernatural faith, useful for salvation, is compatible with only probable knowledge of revelation; indeed with fear, by which one fears that perhaps God has not spoken.” And the Supreme Pontiff Pius IX (Qui pluribus, encyclical, November 3, 1846) teaches: “Human reason indeed, lest it be deceived and err in a matter of such importance, ought diligently to inquire into the fact of divine revelation, so that it may be certain for itself that God has spoken, and may exhibit to Him, as the Apostle most wisely teaches, a reasonable service.” St. Thomas had already taught these things (Contra Gentiles, book 3, c. 154), saying: “Because the proposed speech needs confirmation in order that it be received, unless it is manifest through itself, and those things which are of faith are not manifest to human reason, it was necessary that something be applied by which the speech of those preaching the faith would be confirmed. But it could not be confirmed by any principles of reason by way of demonstration, since those things which are of faith exceed reason. Therefore it was necessary that the speech of the preachers be confirmed by certain signs, by which it would be manifestly shown that speech of this sort proceeded from God.” But it suffices to have hinted at these things, since we expressly demonstrated them in the treatise On the Infused Virtues (disp. 3, art. 8).
160. From these things it is easily inferred that there can be some means for knowing revelation with certainty; and that to deny this possibility is finally the same as to deny the possibility of revelation itself. For if there were no means by which revelation could be rendered certainly credible, man could never firmly believe God speaking. But it would be repugnant to divine wisdom to manifest some truths to us by His own speech if it were impossible for us to adhere to them with the mind; just as someone would act in vain, and therefore foolishly, who directed his speech to a deaf person who could in no way hear or perceive what the other puts forward.
161. In truth, on the hypothesis that revelation has been made, if no means could be available leading with certainty to knowledge of it, one of these two things would have to be conceded: either it would matter little whether man believed or did not believe God speaking; or it would matter little whether he believed rationally or otherwise. Now the first, as we were just recalling, is openly repugnant; the second appears evidently irrational, all the more because from it would follow that man could indifferently embrace one or another religion, although this has already been demonstrated to be erroneous and impious against the relative indifferentists.
162. Indeed it is proper to divine providence that it lead all things to their ends through means conformable to their nature. Therefore, on the hypothesis that revelation has been made, if man is bound to believe God speaking, God must lead man to believing by those means which are conformable to rational nature. But it belongs to rational nature to believe rationally; nor would one rationally believe something to be divinely revealed without a sufficient motive confirming the fact of revelation. Therefore motives of this sort must be present, nor can they be lacking to divine providence. To this point, therefore, belongs that saying of Blessed Peter (1 Pet. 3:15): “always ready to give satisfaction to everyone asking you a reason for that hope which is in you.” And by the same reason the Apostle says (Rom. 12:1): “your reasonable service.” Hence also the Vatican Council (Dei Filius, ch. 3) testifies that God willed that “the service of our faith be consonant with reason,” and that “the assent of faith is by no means a blind movement of the mind.” Compare what we said in the treatise On the Infused Virtues (n. 677 ff.).
163. Therefore, with these things placed in safety, it remains to inquire what are the means, or criteria, by which divine revelation can certainly be discerned. The Deists of the seventeenth and eighteenth centuries, such as Herbert, Toland, Dodwell, Rousseau, etc., like most rationalists of our time who still retain the name of revelation, judge that the only means of judging the divine origin of a doctrine which is presented as revealed is its conformity with the principles of reason. This criterion is altogether worthy of rationalists. For 1) the conformity of some doctrine with the principles of reason indeed shows that it is true; but in no way does it demonstrate that it is revealed, if it is true that reason can know anything true by its own powers. Revelation is a fact, which needs witnesses in order to be proved true. 2) By this criterion of the rationalists, any doctrine containing mysteries would have to be excluded; for reason cannot positively demonstrate the conformity of mysteries with principles known by the natural light. 3) By the same criterion, any revealed doctrine exhibiting truly supernatural religion would have to be excluded as if a priori; for this exceeds the keenness of the mind. Hence, as a little earlier we heard from St. Thomas (Contra Gentiles, book 3, c. 154): “The speech of those preaching the faith could not be confirmed by any principles of reason by way of demonstration, since those things which are of faith exceed reason”; and he adds that Christian revelation was confirmed “when those preaching such things performed works, healing the sick and performing other mighty deeds, which no one but God could do. Hence the Lord, sending the disciples to preach, said: Heal the sick, raise the dead, cleanse lepers, cast out demons (Matt. 10:8); and it is said: But they, going forth, preached everywhere, the Lord working with them and confirming the word by the signs that followed, Mark 16:20.” 4) It could seem strange that rationalists seek a criterion of revelation, since they reject every revelation. But just as they misuse the word revelation (n. 102), so they assign such a criterion of revelation that, once it has been admitted, nothing else can be believed except what is demonstrated from intrinsic causes to be true. We refuted this error in the treatise On the Infused Virtues (n. 1045 ff.).
164. For many Protestants there is no other criterion for knowing with certainty the divine origin of revealed doctrine besides revelation itself. Namely, they think that revelation takes place interiorly and immediately to each individual, and therefore that each person has what they call the testimony of the spirit. Others, however, acknowledge nothing except a certain instinct by which someone is impelled to believe, without any objective reason manifesting the credibility of revelation. We also refuted these errors in the treatise On the Infused Virtues (n. 706 ff.).
165. Therefore, these things being set aside, in order that the true doctrine in this matter may be understood, it must first be noted that some criteria of revelation are negative, others positive. Those are called negative which, if they are lacking to some doctrine, allow it to be concluded at once that it is not divinely revealed; but if they are present, it can indeed be argued that it can be revealed, yet it is not yet established that it is revealed. Positive criteria, however, are those which, if they are found in some doctrine, exhibit an irrefragable testimony of the divine origin of that doctrine. Again, of the criteria of revelation, some are intrinsic, others extrinsic. Intrinsic are those which, as it were, adhere intrinsically to the doctrine itself, so that to one rightly considering it, it immediately appears as divine. But extrinsic criteria are those which, distinct from the doctrine itself, come upon it from without, as an external testimony confirming its divine origin.
166. Now among negative criteria the principal one is the conformity of the doctrine which is presented as revealed with the principles of reason. That is: 1) if some doctrine which is called revealed contains anything evidently repugnant to certain and evident principles of reason, it is at once rightly established that it is not revealed; for God, who reveals, is Himself the author of the natural light, nor can the author of Truth, or substantial Truth, contradict Himself. Compare what we said in the treatise On the Infused Virtues (n. 1073 ff.). 2) By the same reason, if a doctrine which is called divinely revealed contains anything evidently repugnant either to certain and evident principles of morality, or to the true happiness of man, insofar as this is known certainly and evidently from the light of reason, it must at once be concluded that it is not revealed. For God, who is holiness, cannot propose anything repugnant to holiness; nor, when directing man to true happiness, can He teach anything which stands in the way of it. 3) By the same reason, if the diverse heads of the revealed doctrine itself evidently fight among themselves, it is immediately judged that that doctrine is not from God; for this contradiction, like the preceding ones, would be poured back upon God as author. 4) With proportion, the mode by which some doctrine is said to be propagated from revelation can exhibit a negative criterion. If, for example, it had to be propagated by force or fraud, it would rightly be said that it is not revealed.
167. As regards this criterion it is useful to note these things. 1) The criterion of conformity of revealed doctrine with the principles of reason is not of itself necessarily to be applied. For it is not necessary that we adhere to revealed doctrines because they are evident intrinsically, since they must be adhered to not on account of their intrinsic evidence, but on account of the authority of God revealing, once it is established that He has revealed. Nor is it necessary in order that we assent reasonably; for our assent is reasonable if, without the intrinsic truth of the doctrine being seen through, there is sufficient testimony that it is from God. Compare what we handed down in the treatise On the Infused Virtues (n. 1045 ff.). 2) Indeed the same criterion can only rarely be applied with fruit and without danger, both because revelation can contain mysteries, and also because, as regards even the truths not inaccessible to reason, it labors under nearly the same disadvantages as human reason left to itself without revelation. Hence in the treatise On the Infused Virtues (n. 1027) we showed that, in the inquiry into revelation, the testimonies on which the fact of revelation rests should rather be investigated, without undertaking a philosophical examination of the truths which are called revealed. 3) Hence, as we sufficiently indicated from the beginning, this criterion can be of use when there immediately appears an evident contradiction between the doctrine which is called revealed and the evident principles of reason, morality, etc.; and then of itself it has only negative force. Hence deservedly, by the help of this criterion, the ancient Fathers and Apologists of the Church showed the gentiles that their religion was not of divine origin, since monstrous crimes were sanctioned through it. Likewise even now, by the help of the same criterion, it can easily be shown that Mohammedanism and Buddhism are false religions.
168. The sublimity, beauty, and harmony of the doctrine which is called revealed is usually referred to the positive and intrinsic criterion of revelation. For when that sublimity and harmony is so great that, once the powers of human reason have been inspected, it becomes certainly known that the herald of such a doctrine could not have discovered it from himself, nor learned it from other men, it is deservedly concluded that he received it from God communicating it in an extraordinary and supernatural mode. Hence a criterion of this sort is properly referred to one of the extrinsic criteria, concerning which we shall speak shortly. Meanwhile, observe that the excellence and sublimity of doctrine indeed serve for confirming the faith of those who already believe, or of doctrine already approved by other motives; but it is little apt and suitable for finding true revelation. For the talent of only a few is so cultivated that it can rightly weigh the diverse heads of doctrine and compare them with one another, so that it may admire the sublimity and harmony of the whole revelation. Then also this same criterion is in some way subjective and ambiguous, since it is difficult to determine the degree of sublimity which is required for establishing the matter, and many things which appear sublime to some are contemptible to others, especially when passions urge. This is especially true when mysteries are found in the same doctrine; for then that saying of the Apostle can be verified (1 Cor. 1:18 ff.): “For the word of the cross is indeed foolishness to those who perish; but to those who are saved, that is, to us, it is the power of God. For it is written: I will destroy the wisdom of the wise, and the prudence of the prudent I will reject. Where is the wise man? Where is the scribe? Where is the searcher of this age? Has not God made foolish the wisdom of this world? For since in the wisdom of God the world did not know God through wisdom, it pleased God through the foolishness of preaching to save those who believe. For both Jews seek signs, and Greeks seek wisdom; but we preach Christ crucified: to Jews indeed a stumbling block, and to Gentiles foolishness; but to those called, both Jews and Greeks, Christ the power of God and the wisdom of God.”
169. Wherefore the positive criteria of revelation are chiefly extrinsic, which are certain sensible facts accommodated to the grasp of all, and they are reduced to miracles and prophecies. Hence Christ the Lord Himself said (John 15:24): “If I had not done works which no other has done, they would not have sin.” And the Vatican Council taught (Dei Filius, ch. 3): “In order that the service of our faith might be consonant with reason, God willed that, with the internal helps of the Holy Spirit, there be joined external arguments of His revelation, namely divine facts, and especially miracles and prophecies, which, since they clearly show forth the omnipotence and infinite knowledge of God, are most certain signs of divine revelation and accommodated to the intelligence of all. Wherefore both Moses and the prophets, and most especially Christ the Lord Himself, produced many and most manifest miracles and prophecies; and of the Apostles we read: But they, going forth, preached everywhere, the Lord working with them and confirming the word by the signs that followed. And again it is written: We have the firmer prophetic word, to which you do well to attend as to a lamp shining in a dark place.”
170. We established chiefly by authority (On the Infused Virtues, n. 700 ff.) that Christian revelation, which we shall demonstrate to be the only true one, must be made credible by miracles and other external signs. But now we must scrutinize the inner nature of miracle and prophecy, so that the intrinsic force which they have for proving the divine origin of the doctrine in whose confirmation they are produced may become plain.