The argument from miracles

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2 Over the course of the last few weeks, we have discussed versions of most of the central philosophical arguments for the existence of God. I think that these arguments are interesting and important. Nevertheless, I think that it is fair to say that most religious believers throughout history have not come to believe in God on the basis of the arguments we have discussed so far. The argument we ll be discussing today has probably been discussed less by philosophers than the ones we have already covered, but has probably been more influential in actually convincing people that God exists. This is the argument from miracles. There is a long tradition in Christianity of thinking that various miracles can provide the basis for belief in the existence of God. For example, in Chapter 20 of the Gospel of John, after the story of Thomas, John writes: Now Jesus did many other signs in the presence of (his) disciples that are not written in this book. But these are written that you may come to believe that Jesus is the Messiah, the Son of God, and that through this belief you may have life in his name. The idea seems clearly to be that we can, and should, come to believe on the basis of John s telling us about the miracles performed by Christ. This idea has been widely accepted; St. Augustine, for example, is quoted as saying that he would not be a Christian but for the miracles. This raises the question: can the sorts of testimony that we get from St. John give us good reason for believing in God? In our reading for today, Hume argues that this is not possible; Hume s central claim is that we cannot be justified in believing in God on the basis of testimony about miracles.

3 This raises the question: can the sorts of testimony that we get from St. John give us good reason for believing in God? In our reading for today, Hume argues that this is not possible; Hume s central claim is that we cannot be justified in believing in God on the basis of testimony about miracles. But before evaluating Hume s argument, we should try to get a handle on why someone might think that miracles do provide evidence for the existence of God. How might one argue for the existence of God on the basis of miracles? The following rather straightforward argument suggests itself: The argument from miracles

4 Obviously, the argument is valid, so the only question is whether the premises are true. Hume s argument focuses on the question of whether we have any good reason to believe premise (1). But let s focus first on premise (2). What, exactly, is a miracle? According to Hume, a miracle is a violation of the laws of nature. This might seem puzzling. After all, aren t laws of nature supposed to be universal exceptionless claims? (If we find an exception to a supposed law of nature, it seems that the right response is to say that what we thought was a law of nature in fact is not.) And if this is what laws of nature are, isn t the idea of a miracle just a contradiction? This seems to be a very quick and easy argument against the possibility of miracles. But it is not a very impressive argument. Believers in miracles take there to be moments in history at which God suspends the usual natural order. But because this suspension of the natural order has a supernatural cause, it is natural to think that it is not simply a counterexample to the relevant laws of nature, but rather an exception which, because of the kind of exception it is, does not falsify the law in question for cases in which there is no supernatural intervention. Aquinas gives a definition of a miracle which is, for our purposes, more useful. According to Aquinas, those things are properly called miracles which are done by divine agency beyond the order commonly observed in nature. This is a good a definition of miracle as any, and we will take this to define the term for our purposes. If this is the definition of miracle, then premise (2) of our argument is trivially true. The remaining questions are: is premise (1) true? and Do we have any good reason to believe that it is true?

5 God on testimony that miracles have occurred. He says: The argument from miracles... therefore we may establish it as a maxim, that no human testimony can have such force as 1. There to prove have a miracle, been miracles. and make it a just foundation for any system of religion. 2. If (88) there have been miracles, God exists. This is Hume s conclusion. We now need to understand his argument for it, which begins with some premises about the role of perceptual evidence and testimony in the forming of beliefs. Aquinas gives a definition of a miracle which is, for our purposes, more useful. According to Aquinas, those things are properly 2.1 Testimony called miracles and evidence which are done by divine agency beyond the order commonly observed in nature. Hume s first claim is that we should base belief on the available evidence: This is a good a definition of miracle as any, and we will take this to define the term for our purposes. A wise man, therefore, proportions his belief to the evidence.... He weighs If this is the definition the opposite of experiments: miracle, then He considers premise which (2) of side our is argument supportedis by trivially the greater true. The remaining questions are: is premise (1) true? number and ofdo experiments: we have any To that good side reason he inclines, to believe withthat doubt it is and true? hesitation; and when at last he fixes his judgement, the evidence exceeds not what we How could we properly know call that probability. premise (1)(73-4) is true? Perhaps one could know that (1) is true by witnessing a miraculous event. But let s assume for now that none of us The general moral seems to be correct: when deciding whether to believe or disbelieve have ever actually witnessed a miracle. Then it seems that our only evidence for (1) is the testimony of people that some proposition, we should weigh the evidence for and against it to see whether it makes do claim theto proposition have actually or itswitnessed negation more a miracle. probable. So, it seems that to see whether we have good reason for believing (1), we have to figure out when we are justified in believing something on the basis of testimony. How does this sort of general principle fit with our practice of basing beliefs on testimony? This is Hume one of has the acentral very plausible topics answer: addressed by Hume. Here s what he has to say about it: we may observe, that there is no species of reasoning more common, more useful, and even necessary to human life, than that which is derived from the testimony of men, and the reports of eye-witnesses and spectators.... I shall not dispute about a word. It will be sufficient to observe, that our assurance in any argument of this kind is derived from no other principle than our observation of the veracity of human testimony, and of the usual conformity of facts to the reports of witnesses. (74)

6 2.1 Testimony and evidence The argument from miracles Hume s first claim is that we should base belief on the available evidence: A wise man, therefore, proportions his belief to the evidence.... He weighs the opposite experiments: He considers which side is supported by the greater number of experiments: To that side he inclines, with doubt and hesitation; and when at last he fixes his judgement, the evidence exceeds not what we How could we properly know call that probability. premise (1)(73-4) is true? Perhaps one could know that (1) is true by witnessing a miraculous event. But let s assume for now that none of us The general moral seems to be correct: when deciding whether to believe or disbelieve have ever actually witnessed a miracle. Then it seems that our only evidence for (1) is the testimony of people that some proposition, we should weigh the evidence for and against it to see whether it makes do claim theto proposition have actually or itswitnessed negation more a miracle. probable. So, it seems that to see whether we have good reason for believing (1), we have to figure out when we are justified in believing something on the basis of testimony. How does this sort of general principle fit with our practice of basing beliefs on testimony? This is Hume one of has the acentral very plausible topics answer: addressed by Hume. Here s what he has to say about it: we may observe, that there is no species of reasoning more common, more useful, and even necessary to human life, than that which is derived from the testimony of men, and the reports of eye-witnesses and spectators.... I shall not dispute about a word. It will be sufficient to observe, that our assurance in any argument of this kind is derived from no other principle than our observation of the veracity of human testimony, and of the usual conformity of facts to the reports of witnesses. (74) Hume s basic idea seems to be this: we believe things on the basis of testimony because, in the past, we have found that testimony is normally correct: normally 2 the facts conform to the testimony we receive. Is Hume right about the fact that we have found testimony to be, usually, correct? Does this mean that we should always believe whatever we are told?

7 The general moral seems to be correct: when deciding whether to believe or disbelieve This suggests the following rule: Pascal situates the question of miracles within (one part of) the Christian tradition. But and when at last he fixes his judgement, the evidence exceeds not what we the question properly we call want probability. to answer(73-4) is more general: can miracles play this kind of central role in justifying religious The belief argument of anyfrom sort? miracles We The will general focus onmoral the question seems to be correct: when deciding whether to believe or disbelieve 1. There of whether have been miracles miracles. can justify the religious beliefs of people whosome haveproposition, not themselves we should weigh the evidence for and against it to see whether it makes the proposition or its negation 2. witnessed If there have miracles. been miracles, God exists. more probable. How does this sort of general C. God principle exists. fit with our practice of basing beliefs on testimony? Hume has a very 2 plausible Hume s answer: argument against belief in miracles Hume thinks we may thatobserve, they cannot, that there andisindeed no species that ofno reasoning rational more person common, wouldmore base belief in The argument God on from testimony useful, miracles and that even necessary miracles have to human occurred. life, than Hethat says: which is derived from the testimony of men, and the reports of eye-witnesses and spectators.... I shall 1. There have been not dispute miracles. about a word. It will be sufficient to observe, that our assurance 2. If there have in been anymiracles, argumentgod of this exists. kind is derived from no other principle than our... therefore we may establish it as a maxim, that no human testimony can have observation such force of as theto veracity prove of a human miracle, testimony, and make anditof a the justusual foundation conformity any system of facts of to religion. the reports (88) of witnesses. (74) Hume s basic idea seems to be this: we believe things on the basis of testimony because, in the past, we have Hume s This found that basic is Hume s testimony idea seems conclusion. is normally to be We this: now correct: we believe need to normally 2 things understand the facts on the his conform basis argument of to testimony for it, which the testimony because, begins we receive. the past, we have found with that some testimony premises normally about the correct: role of normally perceptual the facts evidence conform and testimony to the testimony in the we forming receive. of beliefs. Is Hume right about the fact that we have found testimony to be, usually, correct? Does this mean that we should always believe whatever we are told? This can t be right, since we are sometimes told Does contradictory this mean that things. we should And, in always any case, believe Hume whatever does not we think are told? that we should always accept testimony. 2.1 Testimony and evidence No. Testimony is just one piece of evidence among others. And in cases in which testimony contradicts some of Testimony our evidence, Hume s is first just one we claimpiece have is to that of evidence determine we shouldamong others. And in cases in which testimony contradicts some of our which base piece belief of on evidence the available is stronger: evidence: evidence, we have to determine which piece of evidence is stronger: A wise man, therefore, proportions his belief to the evidence.... He weighs the opposite experiments: He considers which side is supported by the greater number of experiments: To that side he inclines, with doubt and hesitation; and when at last he fixes his judgement, the evidence exceeds not what we properly call probability. (73-4)

8 ... therefore we may establish it as a maxim, that no human testimony can have such force as The toargument prove a miracle, from miracles and make it a just foundation for any system of religion. (88) Hume s Thisbasic Hume s idea seems conclusion. to C. be We God this: now exists. we believe need tothings understand on the his basis argument of testimony for it, which because, begins the past, we have found with that some testimony premises normally about the correct: role of normally perceptual the facts evidence conform and testimony to the testimony in the we forming receive. of beliefs. Hume s Does this basic mean idea that seems we to should be this: always we believe believe things whatever on the we basis are told? of testimony This can t because, right, in since the past, we are we sometimes have found told that contradictory testimony things. is normally And, correct: in any case, normally Hume the does facts not conform think that to the we testimony should always we receive. accept testimony. 2.1 Testimony and evidence Testimony is just one piece of evidence among others. And in cases in which testimony contradicts some of our Testimony evidence, Hume s is we have first just one to claimpiece determine is that of evidence among others. And in cases in which testimony contradicts some of our which we should piece base of evidence belief on the is stronger: available evidence: evidence, we have to determine which piece of evidence is stronger: A wise man, therefore, proportions his belief to the evidence.... He weighs the opposite experiments: He considers which side is supported by the greater number of experiments: To that side he inclines, with doubt and hesitation; and when at last he fixes his judgement, the evidence exceeds not what we properly call probability. (73-4) This This suggests The suggests general the following the moral following seems rule rule: about to be when correct: we should, when deciding and should whether not, believe to believe testimony or disbelieve about some event occurring: some proposition, we should weigh the evidence for and against it to see whether it makes the proposition or its negation more probable. We should only believe testimony about the occurrence of some event E if the Howprobability does this sort of the of general testimony Hume s principle being principle fit true with is higher about our practice than testimony the of basing probability beliefs of E s on testimony? not occurring. Hume has a very plausible answer: the testimony unless the following is the case: we may observe, that there is no species of reasoning more common, more useful, and even necessary The probability to human of the life, testimony than that being which false is derived < the from the testimony of men, probability and the reports of M occurring. of eye-witnesses and spectators.... I shall not dispute about a word. It will be sufficient to observe, that our assurance in any argument of this kind is derived from no other principle than our observation of the veracity of human testimony, and of the usual conformity

9 Hume s basic idea seems to be this: we believe things on the basis of testimony because, in the past, we have found that testimony is normally correct: normally the facts conform to the testimony we receive. The argument from miracles This suggests the following rule about when we should, and should not, believe testimony about some event occurring: 2. If there One have conclusion: been miracles, testimony God isexists. one, but not the only, source of evidence which we should use when forming a belief. Testimony Hume s principle is relevant about because testimony it has a (relatively) high probability of being true. But, like any evidence, this can be overridden by other sources of evidence (like, for example, We should contrary not believe testimony) that which M happened have give on a the highbasis probability of to the negation of the proposition the testimony in question. unless the following is the case: We should only The believe probability testimony of the about testimony the occurrence being false of < some the event E if the probability of the probability testimony 2.2 of being M Testimony occurring. true is about higher miracles than the probability of E s not occurring. We now need to apply these general points about testimony and evidence to the case of Hume This applies suggests miracles. this principle the One following conclusion explicitly principle seems to the about to case follow of miracles: miraculous immediately: events: That no testimony is sufficient to establish a miracle, unless the testimony be of such a kind, that its falsehood would be more miraculous, than the fact, which it endeavors to establish... (77) Suppose Thewe problem have testimony for the believer that some in miracles miraculous is that event miracles, M happened. being departures Hume is from say that the we lawsshould not believe What it would mean for the falsehood of the testimony to be more miraculous than the occurrence of the M happened of nature, on seem the basis to beof exactly the testimony the sorts unless of events the following which weis should the case: not expect to happen. relevant event? It would mean that the probability of the testimony being false is even lower than the As Hume puts it: probability of the event in question happening. And this is exactly what Hume s principle about testimony The probability of the testimony being false < the probability of M occurring. should lead us to expect. A miracle is a violation of the laws of nature; and as a firm and unalterable

10 Pascal situates the question of miracles within (one part of) the Christian tradition. But 2. If there One have conclusion: been miracles, testimony God isexists. one, but not the only, source of evidence which we should use the question we want to answer is more general: canhume s miracles principle play this about kindtestimony of central The C. argument when God exists. from forming miracles a belief. Testimony is relevant because it has a (relatively) high probability role in justifying religious belief of any sort? of being true. But, like any evidence, this can be overridden by other sources of evidence 1. There have (like, been formiracles. example, contrary testimony) which We have should givenot a high believe probability that M happened to the negation the basis of We will focus on the question of whether miracles can justify the religious beliefs of people 2. If there have of the been proposition miracles, in God question. exists. the testimony unless the following is the case: who have not themselves witnessed miracles. We should only believe testimony about the occurrence The probability of some of the event testimony E if the being false < the probability of the testimony 2.2 being Testimony true is about higher probability miracles than the of probability M occurring. 2 Hume s argument against belief in miraclesof E s not occurring. We now need to apply these general points about testimony and evidence to the case of Hume This applies suggests miracles. Hume this thinks principle the One following that conclusion explicitly they principle cannot, seems to the about to case and follow indeed of miracles: miraculous immediately: that noevents: rational person would base belief in God on testimony that miracles have occurred. He says: The argument from miracles Hume s principle about testimony. That no testimony is sufficient to establish a miracle, unless the testimony 1. There have be. been. of. therefore such miracles. a kind, we may that its establish falsehood it as would a maxim, be more miraculous, than the fact, We that should no not human believe testimony that M happened can on the basis of th 2. If there have which have been such it endeavors miracles, force asgod to to establish prove exists. a miracle,... (77) and make testimony it a just unless foundation the following for any is the case: system of religion. (88) C. Suppose God The exists. we problem have testimony for the believer that some in miracles miraculous is that event miracles, M happened. being departures Hume is from say that the we lawsshould not believe th What it would mean for the falsehood of the testimony to be more miraculous The probability than of the the occurrence testimony of being the false < the M happened of nature, on seem the basis to beof exactly the testimony the sorts unless of events the following which weis should the case: not expect to happen. relevant event? It would mean that the probability of the testimony being probability false is of even M occurring. As This Hume is Hume s puts it: conclusion. We now need to understand his argument for it, lower which than begins the probability of with the event in question happening. And this is exactly what Hume s principle about testimony The probability some premises of the about testimony the role being of perceptual false < the evidence probability and of testimony M occurring. the forming should lead us of beliefs. to expect. A miracle is a violation of the laws of nature; and as a firm and unalterable This We now is one want experience plausible to know reading has why established Hume of what thinks it these would that laws, a mean principle the for proof the of falsehood this against sort shows a of miracle, the that testimony from we are the to never be more justified miraculous in believing th We now the testimony want occurrence to about know veryof why nature miracles. the Hume relevant thinks of the event. that a principle of this sort shows that we are never justified in believing testimony about miracles. fact, is as entire as any argument from experience can 2.1 Testimony and evidence possibly be imagined... There must be a uniform experience against every To do We To do this, now this, we need want we miraculous need to know to figure event, why figure out how Hume out how otherwise to thinks to determine determine the that event the a principle the relevant would relevant not of probabilities: this merit sort probabilities: that shows appellation. the that of probability we the are testimony (76- of never the testimony justified being false, in being believing and of M false, testimony not occurring. and the probability about Recall 7) miracles. the quote about evidence discussed earlier: Hume s first claim of the is relevant that weevent should not base occurring. belief on Recall the available the quote evidence: about evidence discussed earlier: The implied A wise question man, therefore, is: could testimony proportions ever hisprovide belief to strong the evidence. enough evidence... He to weighs override our massive the opposite evidence experiments: in favor of nature s He considers following which itsside usual iscourse supported (which by is the also greater evidence against number the occurrence of experiments: of the miracle)? To that side he inclines, with doubt and hesitation; and when at last he fixes his judgement, the evidence exceeds not what we properly call probability. (73-4) 2.3 The relevance of religious diversity

11 Hume s principle about testimony. 1. There have. been.. therefore miracles. we may establish it as a maxim, We Hume s that should no not human principle believe testimony about that M testimony happened can on the basis of th The argument 2. If there from have miracles have been such miracles, force asgod to prove exists. a miracle, and make testimony it a just unless foundation the following for any is the case: 1. There have been system miracles. of religion. (88) the testimony unless The probability the following of the is testimony the case: being false < the probability of M occurring. This is Hume s conclusion. We now need to understand his argument for it, which begins The probability of the testimony being false < the with some premises about the role of perceptual evidence and testimony in the forming probability of M occurring. of beliefs. We now want to know why Hume thinks that a principle of this sort shows that we are never justified in believing We now testimony want to about know why miracles. Hume thinks that a principle of this sort shows that we are never justified in believing testimony about miracles. 2.1 Testimony and evidence To do this, we need to figure out how to determine the relevant probabilities: of the testimony being false, and of M To do this, not occurring. we need to Recall figure the out quote how to about determine evidence the discussed relevant probabilities: earlier: the probability of the testimony being false, and the Hume s probability first claim of the is relevant that weevent should not base occurring. belief on Recall the available the quote evidence: about evidence discussed earlier: A wise man, therefore, proportions his belief to the evidence.... He weighs the opposite experiments: He considers which side is supported by the greater number of experiments: To that side he inclines, with doubt and hesitation; and when at last he fixes his judgement, the evidence exceeds not what we properly call probability. (73-4) Hume s idea The seems general to be moral this. When seems we to are be correct: trying to when figure deciding out the probability whether toof believe some event or disbelieve happening in certain Hume s circumstances, idea seems to be this. When we are trying to figure out the probability of some event happening in certain some proposition, we ask: wein should the past, weigh how the frequently evidenceas forthat andevent against been it to observed see whether to occur it makes in those circumstances? circumstances, ask: in the past, how frequently as that event been observed to occur in those circumstances? the proposition Our answer or to its this negation question more will give probable. us the probability of the relevant event. Our answer to this question will give us the probability of the relevant event. So, for example, How does to determine this sort whether of general a principle fair coin flip fit with will come our practice up heads, of basing we ask: beliefs in the onpast, testimony? what percentage of fair coin flips Hume have hascome a veryup plausible heads? We answer: find that ½ of them have; so we take the event of the next fair coin flip coming up head to have a probability of 50%, or 0.5. we may observe, that there is no species of reasoning more common, more But this, Hume thinks, is enough to show us that we ought never to believe testimony regarding miraculous useful, and even necessary to human life, than that which is derived from the events. testimony of men, and the reports of eye-witnesses and spectators.... I shall not dispute about a word. It will be sufficient to observe, that our assurance in any argument of this kind is derived from no other principle than our

12 One conclusion: testimony is one, but not the only, source Hume s of evidence principle whichabout we should testimony use The argument when from forming miracles a belief. Testimony is relevant because it has a (relatively) high probability of being true. But, like any evidence, this can be overridden by other sources of evidence (like, for example, contrary testimony) which have give a high probability to the negation the testimony unless the following is the case: The argument of thefrom proposition miracles in question. Hume s principle about testimony. C. God 1. exists. There have been miracles. The We probability should not of believe the testimony that M happened being false on < the basis of th 2.2 Testimony about probability of M occurring. testimony miracles unless the following is the case: Hume s idea seems We nowto need be this. to apply When these we are general trying points to figure aboutout testimony the probability The and probability evidence of some of to the event testimony casehappening of being false < the certain circumstances, miracles. One we ask: conclusion in the past, seemshow to follow frequently immediately: as that event probability been observed of M occurring. to in those circumstances? Our answer to this question will give us the probability of the relevant event. That no testimony is sufficient to establish a miracle, unless the testimony So, for example, to be determine of such awhether kind, that a its fair falsehood coin flip would will come be more up heads, miraculous, we ask: thanin the fact, Hume s idea seems to be this. When we are trying to figure out the probability of some past, event what happening percentage in certain of fair coin flips have which circumstances, come it endeavors we ask: up in heads? to the past, We establish how find frequently that... ½ (77) of them as that have; event so been we take observed the event to occur of the in next those fair circumstances? coin flip coming up head to have a probability of 50%, or 0.5. Our answer to this question will give us the probability of the relevant event. The problem for the believer in miracles is that miracles, being departures from the laws But this, Hume ofthinks, nature, is seem enough to beto exactly show us thethat sortswe of ought eventsnever which to webelieve should not testimony expect to regarding happen. miraculous events. This, Hume As Hume thinks, puts is enough it: to show us that we ought never to believe testimony regarding miraculous events: A miracle is a violation of the laws of nature; and as a firm and unalterable experience has established these laws, the proof against a miracle, from the very nature of the fact, is as entire as any argument from experience can possibly be imagined... There must be a uniform experience against every miraculous event, otherwise the event would not merit that appellation. (76-7) Hume s Hume s point is The point that implied is miracles that question miracles are always is: are could always departures testimony departures from ever provide the from ordinary the strong ordinary laws enough of laws nature. evidence of nature. But to override the But ordinary the ordinary laws laws of of nat nature are are regularities regularities our massive which which evidence have have been in favor been observed ofobserved nature s to hold following to hold 100% its 100% of usual the of course time. the time. Of (which course, Of iscourse, also we evidence have we not have observed not testimony observed be correct testimony against 100% to the be of occurrence the correct time. 100% Hence, of theof miracle)? the probability time. Hence, of the testimony probability regarding of testimony a miracle regarding being false a miracle will always be being greater false will than always the probability be greater of than the the miraculous probability event; of the and miraculous then it follows event; from and Hume s then it follows principle from about Hume s testimony tha principle we about should testimony never accept that the we should testimony. 2.3 never The relevance accept of the religious testimony. diversity

13 2. If there The argument have been from miracles, miracles God exists. C. God 1. There exists. have been miracles. the Hume s principle about testimony testimony unless the following is the case: The probability of the testimony being false < the the testimony unless the following is the case: probability of M occurring. The probability of the testimony being false < the Pascal situates the question of miracles within (one probability part of) the of M Christian occurring. tradition. But Hume s idea seems to be this. When we are trying to figure out the probability of some event happening in certain the question we want to answer is more general: can miracles play this kind of central circumstances, Hume s idea we seems ask: in to the be past, this. When how frequently we are trying as that to figure event out been the observed probability to occur of some in those event circumstances? role in justifying religious belief of any sort? happening in Our answer certain to circumstances, this question we will ask: give in us the the past, probability how frequently of the relevant as that event. event been observed to occur in those circumstances? We will focus Our answer on the question to this question of whether will give miracles us the can probability justify the of religious the relevant beliefs event. of people Hume s point who is that havemiracles not themselves are always witnessed departures miracles. from the ordinary laws of nature. But the ordinary laws of nature are regularities Hume s point which is that have miracles been observed are always to hold departures 100% of from the the time. ordinary Of course, laws of we nature. have not But observed the ordinary testimony laws to of be correct nature 100% are regularities of the time. which Hence, have the probability been observed of testimony to hold regarding 100% of a the miracle time. being Of course, false will we have always not be greater observed than the testimony probability to of be 2the correct miraculous Hume s 100% argument of event; the time. and against then Hence, it follows the belief probability from in miracles Hume s of testimony principle regarding about testimony a miracle that we should being never false will accept always the be testimony. greater than the probability of the miraculous event; and then it follows from Hume s principle about testimony that we should never accept the testimony. Hume thinks that they cannot, and indeed that no rational person would base belief in Hence And Hume s God this is conclusion: testimony that miracles have occurred. He says: precisely Hume s conclusion:... therefore we may establish it as a maxim, that no human testimony can have such force as to prove a miracle, and make it a just foundation for any system of religion. (88) On this reading, Hume s argument depends upon the following assumption: This is Hume s conclusion. We now need to understand his argument for it, which begins with some premises about the role of perceptual evidence and testimony in the forming of beliefs. The zero probability principle If some event has never been observed to occur before, then the 2.1 probability Testimony of it and occurring evidence is 0%.

14 Hume s principle about testimony the testimony unless the following is the case: The probability of the testimony being false < the probability of M occurring. On this reading, Hume s argument depends upon the following assumption: The zero probability principle If some event has never been observed to occur before, then the probability of it occurring is 0%. This is what enables Hume to conclude that we can never be justified in believing testimony about a miracle, since, as he plausibly assumes, the probability of the testimony being false will always be > 0. Interestingly, this principle also seems to be enough to establish a stronger claim: one is never justified in believing in the existence of miracles, even if one is (or takes oneself to be) an eyewitness. Can you see why? Perceptual experiences of the world, like testimony, don t conform to the facts 100% of the time. So, the probability of a miraculous event M occurring will always, given the above principle about probabilities, be less than the probability of one s perceptual experience being illusory, since the latter will always be > 0. Hence, it seems, one would never be justified in believing in the existence of a miracle, even on the basis of direct perceptual experience. This might at first seem like a good thing for Hume s argument: it shows not just that one an never believe in miracles on the basis of testimony, but also that one can never believe in them for any reason at all! But in fact this brings out a problem for the zero probability principle.

15 Hume s principle about testimony the testimony unless the following is the case: The probability of the testimony being false < the probability of M occurring. The zero probability principle If some event has never been observed to occur before, then the probability of it occurring is 0%. Perceptual experiences of the world, like testimony, don t conform to the facts 100% of the time. So, the probability of a miraculous event M occurring will always, given the above principle about probabilities, be less than the probability of one s perceptual experience being illusory, since the latter will always be > 0. Hence, it seems, one would never be justified in believing in the existence of a miracle, even on the basis of direct perceptual experience. This might at first seem like a good thing for Hume s argument: it shows not just that one an never believe in miracles on the basis of testimony, but also that one can never believe in them for any reason at all! But in fact this brings out a problem for the zero probability principle. Consider the following sort of example: You are a citizen of Pompeii in AD 79, and there is no written record of the tops of mountains erupting and spewing forth lava. Accordingly, following the zero probability principle, you regard the chances of such a thing happening as 0%. On the other hand, you know that your visual experiences have been mistaken in the past, so you regard the chances of an arbitrary visual experience being illusory as about (say) 1%. Then you have a very surprising visual experience: black clouds and ash shooting out of nearby Mt. Vesuvius. What is it rational for you to believe?

16 Hume s principle about testimony the testimony unless the following is the case: The probability of the testimony being false < the probability of M occurring. The zero probability principle If some event has never been observed to occur before, then the probability of it occurring is 0%. Consider the following sort of example: You are a citizen of Pompeii in AD 79, and there is no written record of the tops of mountains erupting and spewing forth lava. Accordingly, following the zero probability principle, you regard the chances of such a thing happening as 0%. On the other hand, you know that your visual experiences have been mistaken in the past, so you regard the chances of an arbitrary visual experience being illusory as about (say) 1%. Then you have a very surprising visual experience: black clouds and ash shooting out of nearby Mt. Vesuvius. What is it rational for you to believe? This sort of case seems to show that the zero probability principle is false. Other such examples involve falsification of well-confirmed scientific theories. So, if Hume s argument depends on the zero probability principle, it is a failure. But this doesn t quite mean that Hume s argument is a failure. Sometimes an argument relies on a false premise, but can be fixed by finding another premise which both avoids the problems with the original one, and still delivers the intended conclusion. So we should ask: can we come up with another principle, which would avoid these sort of counterexamples while still delivering the result that Hume wants?

17 Hume s principle about testimony the testimony unless the following is the case: The probability of the testimony being false < the probability of M occurring. So we should ask: can we come up with another principle, which would avoid these sort of counterexamples while still delivering the result that Hume wants? It seems that we can. All Hume s argument needs, it would seem, is the following trio of assumptions: (a) If some event has never been observed to occur before, then the probability of it occurring is at most X%. (b) The probability of a piece of testimony being false is always at least Y%. (c) Y>X X does not have to be zero, as the zero probability principle assumes; it is enough for Hume s argument that it be some number which is always lower than the probability of testimony being false. Suppose, for example, that the probability of an event of some type which has never before been observed is at most 1%, and that there is always at least a 10% chance of some testimony being false. If we assume Hume s principle about testimony, would this be enough to deliver the conclusion that we are never justified in believing in miracles on the basis of testimony? No, because one can get testimony from multiple witnesses. Suppose that we have three witnesses, each of whom are 90% reliable, and each independently reports that M has occurred. Then the probability of each witness being wrong is 10%, but the probability of all three being wrong is only 0.1%. This, by the above measure, would be enough to make it rational to believe that M happened on the basis of testimony.

18 Hume s principle about testimony the testimony unless the following is the case: The probability of the testimony being false < the probability of M occurring. It seems that we can. All Hume s argument needs, it would seem, is the following trio of assumptions: (a) If some event has never been observed to occur before, then the probability of it occurring is at most X%. (b) The probability of a piece of testimony being false is always at least Y%. (c) Y>X Suppose, for example, that the probability of an event of some type which has never before been observed is at most 1%, and that there is always at least a 10% chance of some testimony being false. If we assume Hume s principle about testimony, would this be enough to deliver the conclusion that we are never justified in believing in miracles on the basis of testimony? No, because one can get testimony from multiple witnesses. Suppose that we have three witnesses, each of whom are 90% reliable, and each independently reports that M has occurred. Then the probability of each witness being wrong is 10%, but the probability of all three being wrong is only 0.1%. This, by the above measure, would be enough to make it rational to believe that M happened on the basis of testimony. So it seems that the possibility of multiple witnesses shows that (a)-(c) are not enough to make Hume s argument against justified belief in miracles on the basis of testimony work no matter what values we give to X and Y. (Of course, it is important to distinguish between having testimony from multiple witnesses and having testimony from a single witness who claims there to have been multiple witnesses.) But what if we have just one witness. In those cases, won t Hume s principle about testimony provide a good argument against the rationality of believing in miracles?

19 Hume s principle about testimony the testimony unless the following is the case: The probability of the testimony being false < the probability of M occurring. But what if we have just one witness. In those cases, won t Hume s principle about testimony provide a good argument against the rationality of believing in miracles? Even this can be called into question, because there is good reason to doubt whether Hume s principle about testimony is itself true. This principle can sound sort of obvious; but it isn t, as some examples show. First, what do you think that the probability of the truth of testimony from the writers of the South Bend Tribune would be? Let s suppose that you think that it is quite a reliable paper, and that its testimony is true 99.9% of the time, so that the probability of its testimony being false is 0.1%. Now suppose that you read the following in the South Bend Tribune: The winning numbers for Powerball this weekend were What are the odds of those being the winning numbers for Powerball? Well, the same as the odds of any given combination being correct, which is 1 in 195,249,054. So the probability of the reported event occurring is %. So, if Hume s principle about testimony is correct, one is never justified in believing the lottery results reported in the paper, or on the local news, etc. But this seems wrong: one can gain justified beliefs about the lottery from your local paper, even if it is the South Bend Tribune. You may want to think about how, if at all, Hume s principle could be modified to avoid these counterexamples.

20 Hume s principle about testimony the testimony unless the following is the case: The probability of the testimony being false < the probability of M occurring. You may want to think about how, if at all, Hume s principle could be modified to avoid these counterexamples. If it cannot be fixed, then Hume fails to show that it is never rational to believe in miracles on the basis of testimony. This, of course, does not show that we are currently rational to believe in miracles on the basis of the sorts of testimony we might use as evidence. To decide this question, at least three further issues would need investigation. 1. What are the rules which govern rational acceptance of testimony? If Hume s principle about testimony is not right, then what is? 2. How good is the evidence for events which seem to be exceptions to the usual natural order? This would involve historical investigation into questions like the following: How many witnesses were there? How reliable were those witnesses? Did they have anything to gain by lying? Etc. 3. When is good evidence that some event is an exception to the usual natural order also good evidence of supernatural intervention? These are all very difficult questions to answer. What I think the discussion of Hume shows is that to decide the relevance of miracles to religious belief, questions like these are the important ones. There is no argument - at least no obvious argument - of the sort Hume sought against belief in miracles.