Thought experiments on the historicity of Jesus-1: The contamination principle

Readers may recall an earlier post on the question of whether the Jesus of the Bible is based, however loosely, on an actual historical figure living in that region of the world at that time (as claimed by the historicists) or whether he is an entirely fictional character based on myths and legends (as asserted by those labeled as mythicists). It should be noted that this particular debate does not involve religious people and has nothing to do with whether Jesus did miracles, rose from the dead, and all the other things that signaled that he was divine, which both sides are willing to dismiss as fictional.

Much of the discussion is based on the extent to which the earliest reports of Jesus’s life can be taken at face value. These are the four gospels, the writings of Paul, and a few other sources that refer to some figure like Jesus but that may have been influenced by those five basic documents.

At heart this argument is empirical, whether there is credible data and evidence to support the claim of existence. But philosopher Stephen Law of the University of London has waded into the debate and shown how philosophy, using carefully crafted thought experiments, can help in clarifying questions and sharpening arguments.

Law says that the reliability of the Gospel’s and Paul’s accounts of the ordinary (i.e., not miraculous) elements of Jesus’s life are central to this debate. If those are not credible, then the whole case for a historical Jesus goes up in smoke. In order to judge this issue, Law uses two principles P1 and P2. The first one will be familiar to most readers.

P1: Where a claim’s justification derives solely from evidence, extraordinary claims (e.g. concerning supernatural miracles) require extraordinary evidence. In the absence of extraordinary evidence there is good reason to be sceptical about those claims.

The second one is a new argument (to me at least) and he calls it the ‘contamination principle’.

P2: Where testimony/documents weave together a narrative that combines mundane claims with a significant proportion of extraordinary claims, and there is good reason to be sceptical about those extraordinary claims, then there is good reason to be sceptical about the mundane claims, at least until we possess good independent evidence of their truth.

He points out that the authors of the Gospels wrote much stuff about a man named Jesus who preached and did things that are quite ordinary, and then throw in the miraculous events (he counts about thirty five) from time to time. The historicists argue that we should treat these two elements more or less independently and they take the former seriously while dismissing the latter as later embellishments that can be dispensed with.

Law argues that the contamination principle means that if we dismiss the miraculous as fabulous, then that must seriously undermine the credibility of the ordinary as well. He gives a nice thought experiment to support his case. Suppose you are visited by two close friends Ted and Sarah whom you know to be ‘sane and trustworthy’ people and they tell you about a visit they had from someone named Bert who spent some time socializing with them. They provide all manner of mundane details of the visit (what Bert said, what he wore, what he did), none of which are exceptional. You naturally believe them and in the existence of Bert. Why would you doubt it?

But suppose they then start adding bizarre elements to their narrative, in which Bert “flew around their sitting room by flapping his arms, died, came back to life again, and finished by temporarily transforming their sofa into a donkey. Ted and Sarah appear to say these things in all sincerity. In fact, they seem genuinely disturbed by what they believe they witnessed. They continue to make these claims about Bert even after several weeks of cross-examination by me.”

Since they do not provide any evidence to support the extraordinary actions by Bert, you are unlikely to believe they happened at all. The fact that Bert did some perfectly ordinary things does not make his extraordinary actions believable in the absence of strong supporting evidence (P1). Law poses this question: Would you simply dismiss these aspects as fictitious while believing in the reality of Bert or would you begin to seriously doubt whether the visit by Bert ever happened at all? He concludes that you would do the latter.

The important point that Law makes is that if your friends had not added these bizarre elements to their story, you would have simply accepted their claim of the existence of Bert at face value. You would not have demanded that they produce credible evidence of it, say in the form of videotape or his birth certificate and driver’s license or traces of his DNA on their furniture. The fact that they would have no reason to make up such a boring story gives it a kind of default credibility, unless you suspect that your friends are pathological liars.

But when they introduced the supernatural elements into their story, the entire picture changes. Our natural tendency is not to split the narrative into two: to continue to believe in Bert’s existence and the mundane elements of the story while disbelieving in his miraculous actions. We would begin to rightly suspect that the whole story is fictitious and that Bert does not exist at all and would demand independent evidence of that mundane fact. The fact that you cannot explain why your trusted friends would make up this bizarre story would not lessen your skepticism. It would simply be another puzzle to be addressed separately.

I found this to be a pretty good argument, but there’s more to come.

Tomorrow: More on Law’s arguments against the historical Jesus


  1. OverlappingMagisteria says

    I think I agree with the contamination principle, but it might not apply to the gospels and Paul. The reason I would start to doubt the existence of Bert in the example is because the crazy stories that Ted and Sarah are telling about them make me doubt their sanity. If they’re so out of it that they could see Bert flying around the room then it’s not such a far stretch to think that they were hallucinating entirely.

    However, with Jesus we do not have eye-witness stories. The gospels are written significantly after the events and had been passed down orally multiple times before being recorded. I can imagine a Jesus who had legends attached to him at some point, not by the original witnesses but by someone repeating the stories passed down to them. Perhaps confusing the story of Jesus with some other story being passed around. Perhaps exaggerating a real non-miraculous act that Jesus really did perform (Jesus fed a bunch of people with a few fish can turn into thousands of people after some repetitions.)

    The difference is that with Bert, we are hearing from the direct eye-witnesses whose reliability is called into question once the miraculous elements come out. With Jesus we are hearing a story that has already played the game of telephone for 40+ years. We really can’t know the reliability of the original witnesses and there’s a lot of room for embellishment.

    It is a really interesting principle nonetheless and I thank you for sharing it. I look forward to tomorrows continuation.

  2. iknklast says

    As a fiction writer, I find this argument very plausible. When we’re writing a story, we often make up rather mundane events that characters do to make the other events, the ones the story centers around, more credible. So, we may have a perfectly ordinary conversation about a dinner party, say, that sets the stage to make the characters sympathetic, believable.

    When I read the Bible as a fiction writer, I can see all sorts of elements that are frequently used as tools by fiction writers, even in the “mundane” details. As someone who also writes non-fiction, I know that these tools are NOT used by non-fiction writers. (Of course, writing has changed since the first century, so we do have to consider if that is simply looking at the world from a modern standpoint; reading some of the historians of the Roman Empire, it cannot be stated simply and easily that they did not use the tools of fiction in non-fiction, so this is still somewhat “wiggly”).

    I do know that, when I am reading a non-fiction work, if I see even one statement that is blatantly false, it makes me much less likely to accept statements on things I don’t know as much about. I’ll check them for verification in other sources. The Bible as a sourcebook does not pass this test.

  3. sailor1031 says

    Over the years a number of such stories arose about Haile Selassie, who became a ecentral object of Rastafarianism. But Haile Selassie certainly existed. I think like most philosophy this proposition just opens another can of worms without closing any previously opened cans. In any case, what does it matter if a Yeshue Bar Yussef really existed or not? It can’t be proved one way or the other and it makes no difference to the manifest falsity of christianity or to anything else. It is a pointless debate.

  4. OverlappingMagisteria says

    Thanks. I was racking my brains for examples of real world people who have had urban legends tacked onto them. The coffee wasn’t working yet at the time. Haile Selassie is a good example. Caesar and the various miracle claims he’s had is another.

    A agree that the mythicist/historicist debate is entirely tangential to the real important question: Was Jesus God? And the answer to that question is pretty clearly “no.” But it’s in an interesting debate nonetheless for the dorky type who like to pick over minutia (and I mean that in a good way.)

  5. The Rose says


    “Perhaps confusing the story of Jesus with
    some other story being passed around.”

    One would have to know something of the craft of oral tradition, right? I wonder if there was some deal of accuracy with all the repetition. I wonder if we can fairly well doubt a whole lot of confusion about which story is witch.
    Does one confuse Led Zeppelin’s “Whole-lot-of-love” with Queen’s “Fat Bottomed Girls”?

  6. Francisco Bacopa says

    Just want to say that while Law’s argument describes exactly how I would treat people telling me strange stories about their everyday lives, I would not necessarily apply those standards to written accounts. Real stories about real people can be “improved” by changing and adding things. I couldn’t think of a very good example. Thanks Sailor 1031 mentioning Haile Selassie.

    I’ll come out and say that I am a historicist. I think there’s no other way to account for John the Baptist being in the gospels at all. I read the John the Baptist story as a peace offering to a losing faction. There must have been a John faction and a Jesus faction, they came into conflict, the John faction lost, but had John written into the Jesus story as part of the negotiations.

  7. Jared A says

    “We would begin to rightly suspect that the whole story is fictitious and that Bert does not exist at all and would demand independent evidence of that mundane fact. ”

    No, we might suspect that Bert is their LSD dealer.

    One thing I learned in philosophy 101 is that the most important part of a thought experiment is understanding what kind of assumptions are being made throughout.

    I haven’t read the orginal article by Law, but nothing jumps out at me as wrong with the contamination principle. the problem is that the thought experiment is far from convincing, at least as it is portrayed here. As OverlappingMagesteria pointed out, there are a host of implied, non-incidental reasons about why we may or may not believe Ted and Sarah based on their stories.

    If the point of this thought experiment is to show that contamination applies sometimes, than that’s fine--though, again, the example is pretty awkward for the above reason). But if the point of the thought experiment is to show that the principle of contamination is universal, I think it fails pretty wretchedly.

  8. RW Ahrens says

    I could see your point about the factions, if things were likely to have happened that way. But the gospels weren’t negotiating tools, they were religious tracts meant to instruct the faithful, prove the miracles of christ to the doubtful and be an authoritative source to smack down the heretics in other sects. Each separate gospel was written by a different author (or sometimes authors I think) at different times and places for different audiences.

    The John the Baptist character is an element that exists in other “hero” stories similar to the Jesus story which fulfills a theological requirement of such stories -- that the hero was acknowledged by the heavenly power that sent him in a public manner to kick off his ministry.

    The possibility that there may have been an actual historical figure named John the Baptist is simply icing on the cake -- one of those tools fiction writers use to make their stories seem real -- using a known public figure in a novel to add some measure of reality to the story. That his actions in your fictional narrative are actions that character may have taken in real life just makes it more believable.

    But the fact is that if John the Baptist hadn’t existed, he would have had to have been invented anyway, for the Jesus story to work. And in fact, he doesn’t exist in other Gospels.

  9. mnb0 says

    Stephen’s Law is not convincing at all. In the first place he doesn’t show how it applies to say the Roman Kings (ie before the city became a Republic). In the second place, much worse, he is approaching ancient texts with a 21st Century attitude. If you want to understand those texts you have to try to think like an author from Antiquity. It doesn’t appear to me that Law does try.
    Weird that a sceptic like Mano Singham loses his scepticism when it comes to this subject.

  10. Steve Schuler says

    A more recent example of a historically verifiable person who is known to have lived and who also had many miraculous feats attributed to him is Sathya Sai Baba.

    If one were exposed to Baba via anecdotes from followers of his who believed that Baba possesed supernatural powers, employing Law’s contamination principle would suggest that one should question or doubt the existence of Baba himself as well as the likelihood that Baba was able to perform miracles.

    To me it seems more a stretch of the imagination to believe that Jesus was a completely fabricated entity rather than a literary character derived from a person who actually lived. I think that a historical Jesus is a much simpler and likely explanation than a completely contrived and fabricated character with no basis in reality, as the mythicists suggest.

  11. jamessweet says

    I very much liked his Fifth Islander thought experiment later in the piece. In such a case, I would consider it more or less impossible to say whether there was a fifth islander — which is similar to how I feel about the historicity of Jesus question.

  12. OverlappingMagisteria says

    I’m not sure I understand what you are saying, but I see that the quote that you pulled from me might need clarifying either way.

    I was simply giving one example of how a story can change or get additions to it overtime with oral tradition. For example, imagine the following scenario. Someone is repeating the story of Jesus and remembers hearing about a guy who walked on water. The person thinks “That seems like something Jesus could’ve done… yea I think it really was him.” when in reality the person is remembering a different legend. That gets added onto the story and gets repeated with more certainty with every telling.

    This happens all the time, even today. People forget the source of one story and mistakenly place it into another. Inconsistencies and detail get smoothed over to better fit the narrative (consciously or unconsciously) and, after a few repetitions, it becomes embedded into the story.

  13. CJO says


    With Jesus we are hearing a story that has already played the game of telephone for 40+ years. We really can’t know the reliability of the original witnesses and there’s a lot of room for embellishment.

    Note that this assumes historicity. If there was no historical Jesus, there was no historical event c.30 CE, and no set time frame or initial eyewitness account for this putative game of telephone.


    In any case, what does it matter if a Yeshue Bar Yussef really existed or not? It can’t be proved one way or the other and it makes no difference to the manifest falsity of christianity or to anything else. It is a pointless debate.

    I agree that it doesn’t matter for the manifest falsity of christianity, but that’s hardly the only factor that might motivate one to be interested in the subject. The earliest history of Christianity is a legitimate field of inquiry, and if there was no historical figure at its center the consensus view is drastically wrong.

    OM, again:

    Haile Selassie is a good example. Caesar and the various miracle claims he’s had is another.

    Well, which Caesar, and which claims? The primary difference between Greco-Roman history (Tacitus, Suetonius, Plutarch, Dio, Arrian et al) and the gospels is that the gospels are anonymous, unprovenanced texts. Another key difference is that the historians refer to sources and provide their own analysis where their sources contradict each other or narrate improbable events, while this is entirely absent from the gospels. So we might amend the contamination principle somewhat: Tacitus, for instance, narrates miraculous healings performed by Vespasian in Egypt with a great deal of sarcasm and skepticism (typical for that author); such second-hand reports should not be understood to “contaminate” the mundane accounts in which they are found, as the author clearly doesn’t believe them or at the least leaves plenty of room for doubt. Nearly all of the miracle claims found in the Greco-Roman historians fit this mold; none of the miracles in the gospels do.

    Francisco Bacopa:

    I’ll come out and say that I am a historicist. I think there’s no other way to account for John the Baptist being in the gospels at all. I read the John the Baptist story as a peace offering to a losing faction. There must have been a John faction and a Jesus faction, they came into conflict, the John faction lost, but had John written into the Jesus story as part of the negotiations.

    Even if you’re right, this doesn’t entail historicity. What is at issue is exactly what were the beliefs of the Jesus faction. Why could not a group dedicated to the exaltation of a cosmic redeemer figure like Paul’s Christ have come into conflict with a John faction, focussed on a historical baptizing figure?
    In any case, I think you are wrong. John appears at the outset of Mark as Elijah redivivus, the traditionally expected herald of the Messianic age. It is at his baptism of Jesus that God proclaims Jesus his son, and the later digression to relate the death of John foreshadows the passion.

    RW Ahrens:

    But the fact is that if John the Baptist hadn’t existed, he would have had to have been invented anyway, for the Jesus story to work. And in fact, he doesn’t exist in other Gospels.

    He’s in all four of the canonical gospels. What happens is we see increasing dicomfort on the part of the later authors who take up the story in Mark with the idea of Jesus submitting to a baptism administered by him, as in Mark he is said to be baptizing “for the forgiveness of sins”.

  14. Mano Singham says

    The case of Sai Baba is interesting. The big difference is that there is independent evidence of his actual existence so it is not in doubt. If the only thing we had were reports of his existence provided by a few people, and they made miraculous claims, then it would be a parallel case to that of Jesus.

  15. Mano Singham says

    An interesting parallel is that of Socrates. Did he exist? We are not sure. In his case, there is nothing tangible at stake in his existence or non-existence. What we value are his teachings, whomever they can be ascribed to. Since there is nothing in the stories about him that require miraculous powers, the stories of his existence are not ‘contaminated’ and so do not draw the same level of skepticism.

  16. OverlappingMagisteria says

    “Note that this assumes historicity.”

    Correct it does. My purpose in that was to say that the contamination principle does not disprove a historical Jesus. IF a historical Jesus existed, there are many ways in which fanciful stories could have been attached to him.

    Personally, I am neither a mythicist or historist; I don’t know enough to really make a stand for either. You could call me agnostic on that question. I am only pointing out that I don’t think that the contamination principle does much to support mythicism.

    As to Caesar, there have been miraculous claims added to him (such as Julius Caesar being urged by a divine messenger to cross the Rubicon, and Caesar Augustus being born of a virgin.) Though that was just an example and other have given better ones.

  17. RW Ahrens says

    I have to bow to superior knowledge, I am not one who has memorized or extensively studied the content of the bible to that degree, I was going from a faulty memory. Thanks for the correction.

  18. CJO says

    As to the Caesars, it’s not sufficient to make a vague gesture at added claims of miracle. You have to look at the specific work in question, and how the author presents the claim, as I did for Tacitus on Vespasian, and compare that to the gospels. My contention is that not one of the miraculous claims made by historians of the Roman era even resembles the accounts of miracles by Jesus on the key parameters: genre, provenance, skeptical treatment/alternative versions, and reference to sources. Suetonius, for instance, might relate two or three differing accounts (of which one would be a rationalist explanation), while Tacitus, as discussed above, is openly cynical about such claims. You might say that these authors use these devices to isolate their mundane claims from “contamination” by the miraculous or improbable.

  19. The Rose says

    Thanks, OverlappingMagistria. I’m enjoying your comments below as well -- and others too -- interesting subject.

    I can definitely imagine the “story” changing -- and have seen how rumors can change first hand, but as to the “forgeting the source of one story”…didn’t they use a lot of mnemonic devices in the oral tradition? I don’t think a story teller would make a lot of slip ups on accident. And I can also imagine an audience that would hold them to it…”that’s not how it goes!!” Of course I have NO idea -- just wonderin’.

  20. Andrew G. says

    Law’s argument strikes me as being wrong from a Bayesian perspective; what we need to know is P(E1|H) and P(E1|~H), where E1 is the evidence “the Gospels, heavily mythicized accounts of Jesus containing many supernatural claims, exist” and H is the hypothesis “Jesus was a historical person”.

    Law’s argument on the other hand is more like this: “E1 is weaker evidence for H, due to its incorporation of supernatural claims, than E2 would be, where E2 is a hypothetical account of Jesus not incorporating such claims”. i.e. that P(H|E2) > P(H|E1) for the same prior on H.

    (I’m not drawing a distinction here between evidence for and against, so by “weaker evidence for” I include “stronger evidence against”.)

    Applying Bayes’ theorem to Law’s argument we get:

    P(H|E2) > P(H|E1) iff P(E2|H)/P(E2|~H) > P(E1|H)/P(E1|~H)

    (the prior probability of H cancels out, since it’s the same on both sides)

    So Law’s argument is true if and only if the likelyhood ratio for a non-supernatural account existing, for a historical person as compared to an ahistorical person, is greater than that for a supernatural account existing for a historical person as compared to an ahistorical person. On the evidence I don’t think we can conclude this as a general principle; it might be true for specific kinds of evidence (e.g. eyewitness reports) but not others (e.g. hagiography).

    More importantly, Law’s argument does not seem to provide a useful bound on the value of P(E1|H)/P(E1|~H). Even if the argument is true, then as long as P(E1|H)/P(E1|~H) > 1 then it is evidence in favour of H; and we would normally expect P(E2|H)/P(E2|~H) to be not only greater than 1 but much greater, leaving plenty of room for E1.

    So I think it more productive to focus on P(E1|H)/P(E1|~H) on its own merits.

  21. Francisco Bacopa says

    You might be right, though I fail to see how John the Baptist is necessary at all. Though you may be right that there was a real John at some point. He may never have been involved in whatever events led to the creation of the Jesus mythology, but as you pointed out, John might have been added to the gospels simply to improve the story.

    But I am still sticking to my idea that the inclusion of John in the Gospels is evidence of some kind of conflict between two factions. You might not be aware of this but both factions are alive and well today. Obviously there are Christians, but there is also a sect called the Mandaeans. They teach that John the Baptist is the true prophet and that Jesus is a false prophet.

    There are very few Mandaeans alive today. And I suspect that the current political climate in Iraq will be even more oppressive that it is toward Iraq’s Christian minority. But they do live.

    So there were two factions. Most of the John faction switches sides and gets John included in early teachings that predate the Gospels, the remaining John believers move to Iraq and set up a separatist community this survives to this day.

    Plausible, don’t you think?

    I really don’t think the historicist vs. mythicist debate is that important. Why does it even matter? God isn’t real and no one can be his prophet or messiah, even if claims that someone was a messiah are partly based in fact.

  22. Francisco Bacopa says

    But in a few hundred years how much evidence that Sai Baba was a real person will still be around? Oh well, maybe a lot. But what if all the documentation of Sai Baba were done with not even the best of 1st century CE tech. We might be left with a few scattered notes and objective reports, but mostly just the testimony of his most fervent followers.

  23. Francisco Bacopa says

    What do you make of the fact I pointed out in an earlier reply that there exists to this day a tiny religious sect that considers John the Baptist the true prophet and claims Jesus was a false prophet sent to tempt the world away from salvation? And note well: The Mandaeans do not claim that Jesus was made up, they think he was real, but evil.

    It all seems too complicated for a mytho-verse. Some real dudes were back there somewhere.

    I realize this is something of an argument from personal incredulity, but since I really don’t think the evidence is adequate to do much better, that’s the best I can do. I suppose that makes me an agnostic on this issue who leans toward believing in that there was some specific (non-divine, non-inspired) person the Jesus stories were based on.

  24. says

    Andrew posted the above comment on my blog and I just posted this response, for those interested…

    Thanks Andrew G

    The argument takes the form of a challenge to theists to explain why the existence of Jesus is very probable indeed (not just a bit more probable than not) given the evidence. The prob of Jesus existing might be a bit higher than his non-existing, given the evidence. That is not the point. The onus is on the Biblical scholar to explain why they are justified in giving such a very high probability to the existence of Jesus given the evidence. So I think you are misrepresenting the argument in para beginning “So Law’s” aren’t you?

    Your more important point seems to be that if P(E1|H)/P(E1|~H) is greater than 1 then E1 it is evidence in favour of historicity, and it might be greater than one.

    Sure, but show it is. Show it is considerably greater than one.

    And in fact the general principle that introducing significant uncorroborated supernatural elements does considerably weaken the support provided by evidence for a hypothesis is clearly illustrated by the Ted and Sarah and similar cases. That’s to say, such considerations seem to show P(E1|H)/P(E1|~H) is unlikely to be much greater than one. If indeed it is greater than one.

    So you seem just to be ignoring my argument rather than dealing with it, so far as I can see. But I read this quickly so maybe I’ve got wrong end of stick?!

  25. sailor1031 says

    …..”Personally, I am neither a mythicist or historist; I don’t know enough to really make a stand for either.”

    No worries; neither does anyone else.

Leave a Reply

Your email address will not be published. Required fields are marked *