Hume on Miracles: Skepticism, Probability, and the Limits of Evidence

David Hume’s argument against the credibility of miracles, developed in Section X of his Enquiry Concerning Human Understanding (1748), is one of the most famous and most controversial arguments in the history of modern philosophy. The argument has been the subject of intense debate ever since its publication, and it remains a central reference point for contemporary discussions of the relationship between reason and religion, the proper evaluation of evidence, and the limits of human knowledge.

The Argument

Hume’s argument against miracles is based on a principle of probability: when weighing the evidence for two contrary events, the evidence should be proportionate to the relative probability of the events. A miracle, by definition, is a violation of the laws of nature. The evidence for the regularity of nature is overwhelming, and it is therefore extremely improbable that any particular miracle has occurred. The evidence for any particular miracle — even the testimony of many reliable witnesses — can never outweigh the evidence for the regularity of nature.

The argument has the structure of a kind of practical inference. We weigh the evidence for a miracle against the evidence for the regularity of nature. The evidence for the regularity of nature is much stronger than the evidence for any particular miracle, and therefore we should always reject the testimony for the miracle in favor of the testimony for the regularity of nature.

The Definition of a Miracle

The first step in the argument is the definition of a miracle. Hume defines a miracle as “a violation of the laws of nature.” This definition is important because it sets up the contrast between the miracle and the regularity of nature. If a miracle is a violation of the laws of nature, then the evidence for the regularity of nature is evidence against the miracle.

The definition has been criticized by some later philosophers, who have argued that a more adequate definition of a miracle would be a “special act of God” or an “extraordinary religious event.” But Hume’s definition captures an important intuition: that a miracle is, by its very nature, an unusual event, and that the evidence for an unusual event must be correspondingly strong.

The Evidence for the Regularity of Nature

The second step in the argument is the claim that the evidence for the regularity of nature is overwhelming. We have observed, throughout our experience, that the laws of nature are regular. The sun has always risen in the east, the fire has always burned, and the laws of mechanics have always operated in the same way. The uniformity of this experience gives us an extremely strong reason to believe that the laws of nature are regular, and that any apparent violation of these laws is more likely to be a mistake in our observation than a genuine violation.

The claim about the uniformity of nature is sometimes called “the problem of induction,” and it has been the subject of intense philosophical debate ever since Hume. The basic problem is: how do we justify our belief that the future will resemble the past? Hume’s answer was that we cannot justify this belief by reason alone; it is a habit of mind, based on the constant conjunction of events in our experience.

The Evidence for the Miracle

The third step in the argument is the claim that the evidence for any particular miracle is never strong enough to outweigh the evidence for the regularity of nature. The evidence for a miracle is typically the testimony of witnesses, but the testimony of witnesses is fallible. Witnesses may be mistaken about what they saw, they may be deceived by their own expectations, or they may be dishonest. The evidence for the regularity of nature, by contrast, is the uniform experience of all human beings, and it is much more reliable than the testimony of any particular witnesses.

The argument has an important practical implication: the proper response to a claim of a miracle is to be skeptical. The evidence for the miracle is almost never strong enough to overcome the presumption in favor of the regularity of nature, and the proper response to a miracle claim is to look for a natural explanation of the event.

The Responses

Hume’s argument has been the subject of intense debate ever since its publication, and a number of responses have been developed.

The first response is that Hume’s definition of a miracle is too restrictive. A miracle, the argument goes, is not just a violation of the laws of nature; it is a sign of divine action, and the proper response to a miracle is to recognize the divine action. The definition of a miracle in terms of the violation of the laws of nature prejudges the question, and it begs the question against the existence of the divine.

The second response is that Hume’s argument against miracles depends on the uniformity of nature, but the uniformity of nature is itself something that requires explanation. If the laws of nature are not the result of divine action, then their uniformity is a remarkable fact that requires some explanation; if the laws of nature are the result of divine action, then the argument against miracles is undermined.

The third response is that Hume’s argument is self-undermining. The principle of probability that Hume uses — that the evidence should be proportionate to the relative probability of the events — is itself a principle that is based on experience, and it cannot be used to rule out the possibility of events that are contrary to our experience.

The Legacy

Hume’s argument against miracles has had a profound influence on the development of modern philosophy of religion. The argument is one of the central references for the modern critique of religious belief, and it has been used by skeptics, agnostics, and atheists to challenge the credibility of miracle claims. The argument has also been used by theists and by defenders of religious belief to clarify the proper relationship between reason and faith.