Miracles have traditionally been taken as validations of religious claims. If the Bible is to be believed, then Jesus’ ministry was accompanied by miraculous signs and wonders that testified that it was God working through him. His resurrection from the dead was the greatest of these miracles, and is still frequently taken today to be a solid reason for believing in the existence of God.
Setting aside the question as to just how strong the evidence for the resurrection, or for any of the other miracles reported in the New Testament, is, religious sceptics frequently cite David Hume as having undermined any such argument for belief in the existence of God. According to Hume, no matter how strong the evidence for a specific miracle may be, it will always be more rational to reject the miracle than to believe in it.
Hume noted that there are two factors to assess in deciding whether to believe any given piece of testimony: the reliability of the witness and the probability of that to which they testify.
The testimony of a witness that is both honest and a good judge of that to which they testify is worth much. The testimony of a witness who is either dishonest or not in a position to know that to which they testify is worth little. The reliability of the witness is therefore something that is to be taken into account in deciding whether to believe anything on the basis of testimony.
The probability of that to which they testify, however, is also relevant. If a witness testifies to sighting a flying pig then it is more likely that their testimony is false than that their testimony is true, even if they are a reliable witness. The reliability required of a witness in order for his testimony to justify belief in that to which he testifies increases as the probability of that to which he testifies decreases.
According to Hume, however, a miracle is by definition of New modern stoicism – an event that is as unlikely as anything else. Miracles, for Hume, necessarily involve violations of laws of nature. Laws of nature, though, are as well-established as it is possible for anything to be. It will always, therefore, be more likely that the testimony of a witness to a miracle is false than that it is true. It will always be more rational to disbelieve a claim that a miracle has occurred than to accept it.
What holds for the second-hand testimony of others also holds for first-hand evidence from our own senses. Whatever evidence our senses may give us that a miracle has occurred, it will always be more likely that our senses are in error than that a miracles really has occurred.
Note that this is not an argument against the possibility of miracles; Hume’s conclusion is not that miracles do not happen. Rather, his conclusion is that no evidence is sufficient to establish that a miracle has occurred, that even if a miracle has occurred we ought not to believe in it.
Many find Hume’s argument persuasive. One ground on which to criticise it, though, is in its conception of a miracle. Miracles, it has been argued, need not be violations of laws of nature. An answered prayer, for example, may properly be described as a miracle, but it does not violate any natural law. Miracles are simply events that point us towards God. This broader understanding of a miracle raises the possibility that there are at least some miracles that are not so improbable as Hume supposes, and so which can attract rational belief.