Recently I was glancing through various portions of Thomas Aquinas' Commentary on the Letter to the Hebrews, and I found an intriguing section. In section 16, Thomas Aquinas presented a list of the characteristics of a true prophet. Needless to say, this seems very relevant here. The first thing required of true prophets, he says, is that to them are revealed "things which transcend human knowledge"; in short, they need to be recipients of revelation. Second, he says, the prophet must have an understanding of what he or she has received. Thomas gives the example of pagan rulers in the Bible (Pharaoh, Nebuchadnezzar) who received revelation in dreams and visions but who were not prophets because they did not grasp the revelation. Third, Thomas seems to say that the prophet must not mistake or misrepresent the symbols for the symbolized; for "otherwise, he would not be a prophet but a lunatic who apprehends imaginary things as though they were real". Fourth, the prophet must perceive the revelation clearly "as though known through demonstration". Fifth, the prophet must actually convey the revelation in an expressible way. Here he does not specifically stress the need for these revelations to be veridical and from God; this is simply assumed. Elsewhere, however, Thomas Aquinas does declare that "nothing false can come under prophecy" (Summa theologiae II-II, q171, a6, respondeo), and that "prophecy, properly and simply, is conveyed by divine revelations alone; yet the revelation which is made by the demons may be called prophecy in a restricted sense", and so one must beware of false or demonic prophets as well (Summa theologiae II-II, q172, a5, respondeo). The reason why false prophecies can invalidate a prophet (whereas true prophecies are not a firm guarantee) is that a "true prophet is always inspired by the Spirit of truth, in whom there is no falsehood, wherefore he never says what is not true; whereas a false prophet is not always instructed by the spirit of untruth, but sometimes even by the Spirit of truth" (Summa theologiae II-II, q172, a6, ad 2). But it must still be noted, as Thomas Aquinas does in the seventeenth section of his commentary on Hebrews, that "the spirits of prophecy are not always present in the prophet, but only when their minds are enlightened by God".