Summa summae S. Thomae, Tomus III

[Revelation in general is the manifestation of a hidden truth or of an unknown fact.

If a revelation is made by God himself and in an extraordinary or supernatural manner, beyond the ordinary order of his providence, it is called divine.

Moreover, the object of divine revelation can be twofold. For there are certain truths to which even natural reason can attain; but because this reason, weakened by sin, can frequently hesitate even in these and can even err completely, truths of this kind are known more easily, more clearly and more certainly by the aid of revelation, as the Angelic Doctor expressly proves, lib. I Contra gentes, chap. 3|summa-contra-gentiles-liber-primus:liber.1/capitulum.3 and 4. And the Vatican synod teaches the same thing, in the constitution Dei Filius, where we read: « Divine revelation must indeed be credited with the fact that those things which in divine matters are not of themselves inaccessible to human reason can nevertheless, even in the present condition of the human race, be known by all readily, with firm certainty and with no admixture of error. » There are also truths whose knowledge entirely surpasses the perspicacity of the created intellect, such as the dogmas that are properly called mysteries. And it is evident that these truths can be made manifest to an intellectual creature only by God revealing them.

Now certain truths can be revealed by God either to all men indiscriminately, or to a single man or only to some, so that through this one or those few the rest may be taught. If it were done in the former way, which God has in fact never used, the revelation would be called general and common; if in the latter, it must be called peculiar and private. A revelation made by God to someone without any other intermediary is immediate; when it reaches others through the one whom God chose, it is mediate.

Among unbelievers, moreover, some deny every possibility whatsoever of revelation; others represent mediate revelation as in no way suited to man; finally, others attack revelation of the mysteries alone as impossible.

All of these will be refuted in the following articles.]