Hume thought his arguments against miracles applied to prophecy as well. Miracles cannot serve as proof of the truth of Christianity because miracles violate natural law and because our knowledge of them rests on unreliable testimony rather than direct observation. So too prophecy: “What we have said of miracles may be applied, without any variation, to prophecies; and indeed, all prophecies are real miracles, and as such only, can be admitted as proofs of any revelation.”
In a 1999 article in the Journal of the History of Ideas, however, Peter Harrison points out that Hume’s earliest Christian opponents recognized the flaw in extending Hume’s argument from miracles to prophecy.
The evidentiary basis of believe in miracles and belief in prophecy were quite different. Robert Boyle said that “the manifest proofs of prediction continue still” and thus, unlike ancient miracles, they “are as visible as the extent of the Christian religion.”
Samuel Clarke argued that “The Miracles which our Savior worked, were to his first Disciples, who were Eye-witnesses of them, a complete Demonstration of the Truth of his Doctrine,” but that is not the case with those who followed. He admitted that “the Miracles of Christ, and particularly of his Resurrection, which was the greatest of all, is not such an ocular demonstration to After-generations.” Yet, he went on “in some respects, we have the advantage even of Them; We have the Examination of many Ages, the Answers to the Objections of all sorts of Adversaries, the Judgment of the wisest and most considerate Men that have gone before us, and the Evidence of several of the Lord’s prophecies since that time fulfilled.”
The distinction was widely acknowledged. When Samuel Johnson noted that he considered Hume’s arguments against miracles substantially correct, Boswell questioned him: “Talking of Dr. Johnson’s unwillingness to believe extraordinary things, I ventured to say, ‘Sir, you come near Hume’s argument against miracles, That it is more probable certain witnesses should lie, or be mistaken, than that they should happen.’ JOHNSON. ‘Why, Sir, Hume, taking the propositions imply, is right. But the Christian revelation is not proved by the miracles alone, but as connected with prophecies.”