Philosophers continue to debate about David Hume's case against the rationality of belief in miracles. This article clarifies semantic, epistemological, and metaphysical questions addressed in the controversy. It also explains the main premises of Hume's argument and discusses criticisms of them. The article concludes that one's evaluation of Hume's argument will depend on one's views about (a) the definitions of ‘miracle’ and ‘natural law’; (b) the type of reasoning one ought to employ to determine the probability that a particular miracle claim is true; and (c) whether reasonable people proportion their beliefs about the occurrence of miracles to their evidence.
Philosophical debate about miracles focuses on two questions: (1) What do we mean by ‘miracle’? (the semantic question) and (2) Is it reasonable to believe that miracles occur? (the epistemological question). Moreover, since philosophers agree that part of the answer to the semantic question is ‘an event caused by God’, the epistemological question is closely tied to a cluster of metaphysical questions, most fundamentally, (3) Does God exist?
In Book X of An Enquiry Concerning Human Understanding, ‘Of Miracles’ (72–90), the 18th-century Scottish philosopher David Hume answers the semantic and epistemological questions, and some would say, presupposes an answer to the metaphysical question. Subsequent philosophical conversations about miracles almost invariably begin with Hume.
II. Hume on Miracles
Hume defines a miracle as an event that (a) is caused by God (directly, or indirectly through an ‘invisible agent’) and (b) ‘violates’ (or ‘transgresses’) a law of nature (76, 77). This is his answer to the semantic question. Hume then employs this definition in an argument that concludes that it is never reasonable to believe that a miracle has occurred. This is his answer to the epistemological question.
Here is a paraphrase of Hume's main case against the rationality of belief in miracles (73–7):
Premise 1: Reasonable people always proportion their beliefs to the strength of their evidence.
Premise 2: Every law of nature is such that the evidence that it has never been violated is stronger than the evidence that it has been violated.
Premise 3: If a miracle has occurred, it is a violation of a law of nature.
Conclusion: Consequently, reasonable people will never believe that a miracle has occurred.
discussion of premise 1
Though Hume would probably say that the epistemological principle stated in premise 1 applies to all beliefs, what he has in mind here is its application to beliefs about ‘matters of fact’ (as opposed to beliefs about ‘relations of ideas’). A matter of fact concerns the way the world actually is, and a relation of ideas has to do with the connections between our concepts. For instance, a matter of fact is that Hume was a bachelor all his life, and a relation of ideas is that all bachelors are unmarried men. Hume's focus on beliefs about matters of fact in his argument concerning miracles is appropriate, because if miracles occur, their occurrence is a matter of fact about the way the world is. Notice that given Hume's definition of a miracle, stated above, premise 3 of his argument is a relation of ideas (a claim about the content of our concept of a miracle) rather than a matter of fact.
According to Hume, ‘experience is our only guide in reasoning concerning matters of fact’ (73). So Hume assumes that all our beliefs about matters of fact are empirical beliefs. Empirical beliefs are beliefs that are based on our experiences of the world rather than beliefs that are grounded in our rational grasp of the relationships between our concepts. Furthermore, the types of empirical beliefs Hume discusses in this context include both beliefs about particular occurrences (i.e., events) and beliefs concerning generalizations about the relationships between types of events. An example of an event is the coming back down of something you've just thrown up in the air. An example of a generalization about types of events is the statement that everything that goes up comes down. That is, this general claim is that the type of event that involves something going up is always conjoined with (followed by) the type of event of that thing coming back down again.
As Hume's examples show, the evidence for some of our particular beliefs about events will often include general beliefs about relationships between types of events. For instance, our evidence for our particular belief that the bread we are about to eat will nourish us is our general belief, based on our past experience, that ‘all bread nourishes us’. Hume points out that, though some types of events are invariably conjoined with other types of events (as in the case of bread and nourishment), other event-type combinations are variable. Hume's example of a person reasoning about a case of this latter sort is of ‘one, who in our climate, should expect better weather in any week of June than in one of December’ (73). People with such expectations have occasionally been mistaken, because though this generalization about the weather in Great Britain is usually true, it is sometimes false.
We are now in a position to appreciate why it is that Hume says that reasonable people will proportion their beliefs to the strength of the evidence they have for them. In some cases our experience is that two different types of events have been constantly conjoined without a single exception. This is the case with the types of events of eating bread and being nourished. Hume thinks that in such cases reasonable people will have the highest degree of assurance that the bread they are about to eat will nourish them. In Hume's view, believing with this maximal degree of confidence is appropriate because the evidence of experience in this case provides a proof of the particular belief in question. That is, since experience has shown that eating bread is uniformly associated with being nourished, we have the strongest possible experiential evidence that the bread we are about to eat will nourish us.1 Thus, it is reasonable to have the strongest degree of confidence that our expectation is true.
However, in cases in which our experience is not uniform but variable, as it is with weather conditions, the evidence provided by our experience is weaker, and so does not constitute a proof that a given unobserved weather condition in a certain place and during a certain month will be similar to the observed weather conditions at that place and during that month in previous years. In such cases the evidence only supports a particular expectation with some degree of probability or other, short of complete proof (where the degree of probability depends on the frequency with which the types of events in question occur together). Hume points out that reasonable people are more cautious in their expectations when their evidence makes the expected outcome only probable rather than certain, and their degree of caution is correlated with the relative strength of their evidence.
discussion of premise 2
Premise 2 of Hume's argument is about laws of nature. Hume construes laws of nature as contingently true universal generalizations (though this is not his terminology).2 A universal generalization is a statement of the form ‘All As are Bs’. In the case of laws of nature, the ‘A’ and ‘B’ are placeholders for types of events. A universal generalization is contingently true if and only if it is actually but not necessarily true (in the logical or metaphysical sense) that every A is also a B. In the discussion of premise 1 above, the claim that all instances of eating bread are cases of being nourished would qualify as a law of nature in Hume's sense, whereas the claim about weather in Great Britain would not. To say that a universal generalization relating types of events is true is to say that the two types of events it relates are uniformly, invariably, and constantly conjoined. If there is just one instance of an event of type A not also being an event of type B, then the universal generalization that all As are Bs is false. So if it is true (and a matter of fact) that all As are Bs, then according to Hume, it is a law of nature that all As are Bs. If instead there is at least one A that is not a B, then it is not true, and so not a law of nature that all As are Bs.
To say that a law of nature of the form ‘all As are Bs’ has been violated is simply to say that there has actually been an A that was not a B.3 So the law that if you eat bread you will be nourished would be violated if there were just one instance of someone eating bread and not being nourished. Thus, if a law of nature of the form all As are Bs is unviolated, it is a true universal generalization, and if it is violated, then it is true instead that some As are not Bs and so false that all As are Bs. Consequently, for every statement that expresses a law of nature in Hume's sense (as I interpret him), there is a corresponding statement that expresses a state of affairs that would be a violation of that law, and these pairs of statements are logical contradictories. That is, a natural law statement is true if and only if the statement expressing its (possible) violation is false. For instance, it is true that all bread nourishes if and only if it is not the case that there is some bread that does not nourish.
Since natural law statements and statements expressing their violation are contradictories, evidence for one will be evidence against the other. If we have reason to believe that it is a law of nature that all As are Bs, then we thereby have reason to believe that there is no violation of this law, and if we have reason to believe that some As are not Bs, then we have reason to believe that there is no law that all As are Bs.4 What should we do if we have evidence for the claim that all As are Bs and evidence for the claim that some As are not Bs (and so that not all As are Bs)? Since reasonable people will proportion their beliefs to the evidence they have for them, what we should do in such a case depends on whether the evidence for the law is stronger than the evidence against the law or vice versa. If the evidence both pro and con is equally weighty, then we should suspend belief. But Hume says (and this is premise 2), that every law of nature is such that the evidence that it has never been violated is stronger than the evidence that it has been violated. So Hume believes that reasonable people will never believe that a law of nature has been violated. What kinds of evidence do we have for laws of nature and for their alleged violations, and how much of each of these types of evidence do we have?
Since both natural law statements and statements of the alleged violation of a natural law fall into the category of ‘matters of fact’, the kind of evidence required to support each type of statement is experience. However, though the type of experiential evidence necessary to justify both types of claims is perception or observation at the foundational level, on Hume's account of laws of nature these universal generalizations require inductive support as well. With respect to event types A and B, we are justified in believing that all As are Bs if and only if we have observed a sufficient number of As being conjoined with Bs (and no As that fail to be Bs). The type of experiential evidence adequate to justify a claim that an alleged law of nature of the form ‘all As are Bs’ has been violated is instead a single observation on someone's part of some A that is not a B. Now Hume appears to assume that no one among his readers will have access to such perceptual evidence; he discusses only cases in which we have access to testimonial evidence – evidence provided by someone else who claims to have witnessed a miracle. So the type of evidence that supports natural law claims is inductive and the kind that supports natural law violation claims is observational or testimonial.
Why does Hume think that the inductive evidence that supports a natural law claim is always stronger than the (observational or) testimonial evidence that supports the claim that this natural law has been violated? Well, he states that the laws of nature have been established by ‘a firm and unalterable experience’ and that, since ‘a miracle is a violation of the laws of nature . . . the proof against a miracle . . . is as entire as any argument from experience can possibly be imagined’ (76). He also says that there must ‘be a uniform experience against every miraculous event’ (77).5 What is this experiential evidence for the laws of nature (as Hume conceives them) that is ‘firm’, ‘unalterable’, and ‘uniform’ (and therefore constant, invariable, and exceptionless)? Though Hume does not answer this question in any detail, it seems clear that he has in mind the collective experiences of human beings throughout history. Hume implies that it is a law of nature that dead people stay dead. He does so on the grounds that a dead person's coming to life ‘has never been observed, in any age or country’ (77). So Hume implicitly assumes that the universal generalizations that constitute the laws of nature have been established and proven to be true (and thus unviolated) on the basis of human experience in every time and place.
But what about those human beings who provide testimonial evidence that they have observed a violation or falsification of one of these universal generalizations? What, for instance, about the claims of over 500 people to have seen Jesus of Nazareth alive again after his death (Holy Bible, I Corinthians 15.3–8)? If their claims are true, then Hume is wrong to say that a dead person's coming to life ‘has never been observed in any age or country’ (77). Hume is willing to grant the possibility that someone's testimony could establish that there has been a violation of a law of nature. But in order for this to happen, the falsehood of the testimony must be ‘more miraculous’ (and thus less probable) than the alleged miracle for which the testimony is evidence (77). What this seems to boil down to when expressed more simply is that it must be more likely that the person who claims to have witnessed a miracle is telling the truth than that this person is either lying or deceived.
Hume gives two reasons for thinking that, in spite of this theoretical possibility, it can never be established or proven on the basis of testimony that there has been a violation of a law of nature. The first reason is that, even if it should be more likely that a person reporting a violation of natural law is telling the truth than lying or deceived, the strength of this testimonial evidence must be diminished by the strength of the counterevidence – which is the evidence for the claim (in the form of general human experience) that the law of nature in question has not been violated after all. So the best we can hope for is probability rather than proof. The second reason Hume gives for his claim that there cannot be testimonial proof of a natural law violation is that there has never been testimonial evidence of sufficient strength to support the conclusion that alleged eyewitnesses to miracles are more likely telling the truth than lying or deceived. It follows that testimony has never proven nor even made probable a miracle claim. Hume devotes most of Part II of ‘Of Miracles’ (78–90) to his defense of this allegation, but space limitations preclude further discussion of it here.6
discussion of premise 3
In ‘Of Miracles’, Hume does not defend his definition of ‘miracle’ by means of argument, and he does not suggest the possibility that there are any alternative ways to understand the concept. Nor does he provide a justification of or a competitor for his analysis of the concept of natural law, which is included in his definition of ‘miracle’. However, in earlier sections of the Enquiry, Hume argues that natural laws are nothing but descriptions of general causal relationships between events. He then contends that these causal principles are nothing but statements of the constant conjunction of similar events from which we infer effects from causes and vice versa (54–5). As an empiricist, he is skeptical about the existence of unexperienced forces or causal powers in objects or necessary connections between events (39–53). This explains why it is appropriate to say (as articulated above) that he views natural causal laws simply as contingent universal generalizations of the form ‘All As are Bs’ and violations of these laws (miracles) as cases in which there is an A that is a not a B. These universal generalizations are simply summaries of our discoveries of ‘the constant conjunction of similar events’ (As and Bs).7
Since we never discover a force or power that necessitates a connection between As and Bs (e.g., eating bread and being nourished), our only basis for confirming that there is a constant conjunction between them is our repeated experience of their joint occurrence, and the more experience of this sort we have, the stronger our evidence for the truth of the generalization. As we have seen, Hume assumes that the more experiential evidence we acquire that confirms such generalizations, the more experiential evidence we possess that disconfirms counter-claims (violations, miracles).
III. The Semantic Question
Is Hume's answer to the semantic question the only possible one? No. However, given Hume's conception of laws of nature, there does not seem to be any other way to characterize miracles. If it is a law of nature that dead people stay dead (that the event of having died is constantly and invariably conjoined with the event of staying dead), then what could the miracle of a resurrection be but a violation of this law (a falsification of this generalization)? If this is right, then there can be an alternative answer to the semantic question only if there is another way of thinking about natural laws. And there is. Another way to conceive of the laws of nature is to see them as descriptions of what normally (rather than invariably) happens in nature. Given this construal of natural laws, a miracle would be an abnormal, supernatural occurrence.8
From a theistic standpoint, this alternative view of natural law makes a lot of sense.9 If there is a God who created and sustains the universe, then, given what we know from science about how the universe operates, God created and sustains the universe to work in regular ways that are specifiable in terms of natural laws. Moreover, one way to explain how God did this is to say that God created the universe (= nature) and the things in it (= natural objects) to have their own natural powers that enable them to function in these regular ways. God's normal interaction with nature would be to continue to sustain the existence of these objects and powers that God created and to concur with their regular operation (enable them to work as he designed them to work). Natural laws would then describe the specific ways in which natural objects exercise their God-given powers. They would also therefore describe the ways in which God normally interacts with nature (since God's concurrence with the natural powers of things is his normal mode of operation).10 Of course their statement by scientists would not mention God as the ultimate cause; scientific formulations of natural laws would mention only the relevant proximate natural causes and effects (e.g., ‘normally, wine is produced by a long process of grape cultivation and fermentation’).
If natural laws are descriptions of what normally happens in nature, then miracles do not have to be defined as violations of natural laws (in Hume's sense). Instead, a miracle would be a relatively abnormal, unusual, atypical, or extraordinary (and so rare) act of God that would leave natural laws as they are.11 If it is a natural law that normally, dead people stay dead, then it would not be a violation of natural law if God occasionally chose to bring a dead person back to life. In such a case God would bypass or supersede his normal way of doing things with natural objects (concurring with the operation of their natural powers) by ‘intervening’ in the natural order to exercise his power more directly and supernaturally; instead of employing the created natural powers of things as instruments to accomplish his purposes, God would temporarily set these means aside and supplement them with alternative methods. On this view, though everything that happens in the world has God as its ultimate supernatural cause, most of the things that happen can be explained by an appeal to the natural powers of natural objects. Only miracles would require an appeal to God's agency to explain their occurrence.
IV. The Epistemological Question
the evidential status of miracle claims
If this alternative understanding of miracles is true, then Hume's premise 3 is false. However, it is possible to reformulate Hume's argument in terms of the definition of miracles just introduced in such a way as to preserve its support for his claim that it is never reasonable to believe that a miracle has occurred. To see this, suppose that a miracle is a relatively rare event that cannot be explained in terms of a genuine natural law (construed now as a description of a way in which nature normally operates). Now add Hume's assumption that what is usual and thus more frequently observed is more probable than what is unusual and less frequently observed (78). Since miracles are by definition relatively unusual events and natural laws are descriptions of what usually happens, it follows that it is always more probable that an event can be explained in terms of natural laws than that it was a miracle. If reasonable people will always proportion their beliefs to the evidence they have for them, and if the strength of one's evidence is a function of how probable one's belief is relative to that evidence, then one ought always to believe of any given event that it is explainable in terms of natural law rather than that it is a miracle.
But Hume's assumption about what makes events probable and improbable is debatable. It presupposes that a judgment of how probable it is that a particular event occurred must be based on an appeal to a general probability statement arrived at by a process of enumerative induction. But there is an alternative form of inference that can be employed to support such judgments. This other method is abductive reasoning, which is also called ‘inference to the best explanation’.12 What's the difference between these two types of reasoning?
Suppose you are trying to decide how probable it is that someone was raised from the dead. If you employ the process of enumerative induction, you will gather a representative sample of observed cases of people who have died and you will check to see whether these people have stayed dead. To be fair to those people who claim to have seen a dead person come back to life, you might conclude that at least 99.9999% of dead people have remained dead. Then you will infer on the basis of this general probability statement that it is at most only 0.0001% likely that there has been a miracle of resurrection. As a reasonable person who proportions his or her beliefs to the evidence, you have no choice but to conclude that the reported resurrection probably did not occur.
If, on the other hand, you use the process of abductive reasoning to evaluate the probability of a dead person's having come back to life, you will start with all of the relevant observed facts and look for the hypothesis that does the best job explaining them in light of everything else you know or are justified in believing to be true. For example, assuming that it is very likely that Jesus of Nazareth lived, died on a cross, was buried in a well-known tomb which was found empty three days later and was believed by over 500 people to have appeared alive to them, it could be argued, as many Christian apologists do,13 that the best (and therefore most probable) explanation of these facts is that Jesus was really raised from the dead.14 Of course alternative explanations are available, such as that his body was stolen and that the ‘resurrection’ appearances were due to mass hallucinations. But the point is that this approach makes it possible to argue, on the basis of the available evidence, that it is more probable that a miracle occurred than that it did not.
Though Hume would reject this abductive approach (on the grounds that it posits the existence of unobserved causes to explain observed events), he might grant it for the sake of argument and contend that naturalistic explanations of events would always be better (and so more probable) than explanations that treat those events as miraculous. But whether this is the case or not depends on what the person investigating a miracle claim is already justified in believing to be true.
Take the three cases of an atheist (who believes that God does not exist), a theist (who believes that God does exist), and an agnostic (who suspends belief about whether or not God exists). Suppose that all three have sufficiently good reasons to be justified in their positions about God. Since miracles, if they exist, are events that are caused by God, (a) the atheist will have good reason to believe that it is impossible and so improbable that miracles occur; (b) the theist will be justified in believing that miracles are possible (on the grounds that a being exists who can produce them) or even probable (on the basis of the claims that God would perform miracles if he had a good reason to do so and that it is likely that God sometimes has such a reason); and (c) it may be reasonable for the agnostic to believe that it is just as likely that miracles occur as that they do not.15 In short, the initial probability one has good reason to assign to the claim that miracles sometimes occur will vary with one's worldview. Moreover, the value of this prior probability will contribute to the determination of how reasonable it is for one to conclude in a given case that the best explanation of certain observed facts will posit the existence of a miracle to account for them. So a use of the abductive approach may not always favor naturalistic over supernaturalistic explanations of events.16
We have seen that premises 3 and 2 of Hume's argument are debatable. Premise 1 is as well. Would reasonable people always proportion their beliefs to the strength of the evidence they have for them? The answer to this question depends in part on what would count as evidence. If the category of evidence includes only things we believe, then it is arguable that it can be reasonable to believe something that is not based on evidence.17 Examples of such beliefs include perceptual beliefs (which are arguably justified on the basis of perceptual experiences rather than other beliefs) and beliefs which have self-evident propositions as their content (which are arguably justified on the basis of a rational grasp of relations between concepts or properties rather than on the basis of other beliefs). If some beliefs are justified without being based on evidence, then reasonable people can be justified in having such beliefs without having to proportion their belief (i.e., their degree of confidence that the belief is true) to any evidence.
But Hume could grant all of this and yet insist that a belief that a miracle has occurred must be justified on the basis of evidence, because such beliefs are neither evident to the senses nor self-evident. But suppose we are talking about the beliefs of the apostles that Jesus was raised from the dead – a belief they simply found themselves having on the basis of it seeming to them that they were seeing Jesus alive after he died. In such a case they would not have engaged in any reasoning or inference in forming their belief, and so they would not have acquired their belief in Jesus's resurrection on the basis of evidence. Moreover, what about Christians in subsequent generations who believe, on the basis of a religious experience, that they have encountered the risen Christ? Might these people be justified in believing in the miracle of Jesus's resurrection apart from historical evidence and so without having to proportion their belief to the evidence? Some who deny Hume's proportionalist evidentialism have affirmed that beliefs in miracles can be rational apart from propositional evidence.18
But what reasons do such philosophers offer for rejecting evidentialism? Evidentialism has been criticized on the grounds that (a) it is self-defeating (since the thesis of evidentialism itself is neither evident to the senses, nor self-evident, nor justifiable on the basis of evidence and so not rational to believe to be true relative to its own criteria for rationality) and (b) overly restrictive (since if it is true, a number of beliefs that seem clearly to be justifiedly or rationally held would be unjustified or irrational instead, such as memory beliefs and beliefs in other minds, which are arguably justified directly on the basis of certain sorts of experiences rather than being evident to the senses, self-evident, or justified indirectly by an appeal to evidence).19
V. Concluding Remarks
Hume's argument against miracles continues to be discussed by its supporters and detractors. Current debates about it include conversations about the semantic and epistemological questions. This article has highlighted some of the most important focal points of these debates: (1) Should natural laws be characterized as contingent universal generalizations describing the constant conjunction of similar events or instead as descriptions of what normally happens in nature when natural objects and processes are not interrupted by any supernatural agency?; (2) Should the evidential status of miracles be determined on the basis of a relatively narrow process of enumerative induction or by means of abductive reasoning (inference to the best explanation) that takes one's general justified metaphysical beliefs into account?; and (3) Should reasonable people proportion their beliefs about miracles to the evidence they have for them or is it instead possible to be justified in believing that a miracle has occurred on the basis of perceptual or religious experiences rather than propositional evidence?20 Finally, it seems clear that how one thinks it best to answer these questions will depend, to a large extent, on one's background beliefs, such as whether one is a theist or not. So these debates about the semantic and epistemological questions will continue to lead to controversies about metaphysical questions.21
James E. Taylor is currently philosophy professor and chair of the philosophy department at Westmont College in Santa Barbara, California. He received his B.A. in philosophy at Westmont, an M.A. in theology at Fuller Theological Seminary in Pasadena, California, and an M.A. and Ph.D. in philosophy at the University of Arizona in Tucson. He taught in the philosophy department at Bowling Green State University in Bowling Green, Ohio from 1987 to 1993 before joining the faculty at Westmont in 1994. Dr Taylor has published a number of philosophical essays on epistemological topics in such journals as Synthese, Philosophical Studies, American Philosophical Quarterly, Philosophy and Phenomenological Research, Nous, Philosophia, and Philosophical Papers. He has also recently written a book entitled Introducing Apologetics: Cultivating Christian Commitment (Baker Academic, 2006). The courses he teaches are Introduction to Philosophy, Modern and Contemporary Philosophy, Epistemology, Philosophy of Language, and Christian Apologetics. He was recognized as the Westmont College Teacher of the Year in the Humanities Division in 1997. Dr Taylor is a member of Phi Beta Kappa, Phi Kappa Phi, Omicron Delta Kappa, and Phi Sigma Tau (the national philosophy honor society). He is also a member of the American Philosophical Association and the Society of Christian Philosophers.