Reply to James McGrath’s Criticism of Bayes’s Theorem in the Jesus Mythicism Debate

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by Neil Godfrey

Aviezer Tucker

James McGrath in a recent post, Jesus Mythicism: Two Truths and a Lie, made the following criticism of the use of Bayes’s theorem in the Jesus Mythicism debate:

. . . . as I was reminded of the problematic case that Richard Carrier has made for incorporating mathematical probability (and more specifically a Bayesian approach) into historical methods. . . .

If one followed Carrier’s logic, each bit of evidence of untruth would diminish the evidence for truth, and each bit of evidence that is compatible with the non-historicity of Jesus diminishes the case for his historicity.

The logic of this argument is based on a misunderstanding of the nature of historical inquiry and how a historian is expected to apply Bayesian logic. (It also misconstrues Carrier’s argument but that is another question. I want only to focus on a correct understanding of how a historian validly applies Bayesian reasoning.)

In support of my assertion that James McGrath’s criticism is misinformed I turn to a historian and philosopher of history, Aviezer Tucker (see also here and here), author of Our Knowledge of the Past: A Philosophy of Historiography. He treats Bayesian reasoning by historical researchers in depth in chapter three. I quote a section from that chapter (with my own formatting):

There have been attempts to use the full Bayesian formula to evaluate hypotheses about the past, for example, whether miracles happened or not (Earman, 2000, pp. 53–9).

We may compare McGrath’s criticism. He is of the impression that the Bayesian formula is used to evaluate the hypothesis that Jesus did exist. This is a common misunderstanding. If you are confused, continue to read.

Despite Earman’s correct criticism of Hume (1988), both ask the same full Bayesian question:

“What is the probability that a certain miracle happened, given the testimonies to that effect and our scientific background knowledge?”

We may compare McGrath’s criticism again. He is of the impression that the historian using Bayesian logic is asking what is the probability that Jesus existed, given the testimonies to that effect and our background knowledge. If you are still confused then you share McGrath’s misunderstanding of the nature of historical inquiry. So continue with Tucker:

But this is not the kind of question biblical critics and historians ask. They ask,

“What is the best explanation of this set of documents that tells of a miracle of a certain kind?”

The center of research is the explanation of the evidence, not whether or not a literal interpretation of the evidence corresponds with what took place.

(Tucker, p. 99)

In other words, biblical critics and historians ask (Tucker is assuming the biblical critic and historian is using Bayesian logic validly and with a correct understand of the true nature of historical research) what is the best explanation for a document that, say, purports to be by Paul saying he met the James, “the brother of the Lord”.

I use that particular example because — and someone correct me if I am mistaken — Jame McGrath and others believe that passage (Galatians 1:19) makes any questioning of the historicity of Jesus an act of “denialism”. (McGrath does not tell his readers in the post we are addressing what he has in mind as the “clear-cut” evidence for the historicity of Jesus but from previous posts and comments I am convinced that it is the “brother of the Lord” passage in Galatians 1:19 that he has in mind. If I am wrong then someone will no doubt inform me.)

No one, I am sure, would mean to infer that the late and highly respected Philip R. Davies was guilty of denialism when he suggested that the historical methods he applied to the Old Testament should also be applied to the New — a method I have sought to apply to the study of Christian origins ever since I read Davies’ groundbreaking book.

Back to the question. It is the question of what is the best explanation for the passage in our version of Galatians that I have attempted to address several times now.

That is the question that the historian needs to ask. Every decent book I have read for students about to undertake advanced historical studies has stressed, among many other duties, the necessity for the researcher to question the provenance, the authenticity, of the documents he or she is using, and to know all the questions related to such questions from a thorough investigation of the entire field. My several posts have attempted to introduce such questions that should be basic to any historical study.

Tucker, from my reading of his book, would not consider such an exercise to be “denialism”, but sound and fundamental historical method — and even sound biblical criticism.


There are other fallacies and misunderstandings in McGrath’s post but one central point is surely enough for a reply. Some of those missteps could be corrected from a reading of both Tucker’s chapter three and Carrier’s Proving History.

But I can’t resist just one point. The apocryphal tale of chopping down the cherry tree is not evidence for the nonhistoricity of George Washington as implied in McGrath’s post. It is evidence that apocryphal or mythical tales grew around George Washington. Recall once again Tucker’s point. The historian asks what is the best explanation for the tale of the cherry tree. If the best explanation, given our other evidence and background knowledge, is that GW did in fact do the deed, then that is what the historian goes with. But if the best explanation, given our other evidence and background knowledge, is that the tale is apocryphal, then that’s what the historian goes with.

The evidence for the historicity of George Washington is found in other documents and artifacts. The historian looks for the best explanation for these and to date all historians have considered that the best explanation for the details of these is that they testify to the historical existence and activities of George Washington.

Biblical critics would not be dismayed by this process. Most critical scholars do accept that the best explanation for the gospel narratives is that they are the product of much myth-making and theological interpretation surrounding Jesus. Does Galatians 1:19 prove Jesus existed? We cannot say that until we first ask and investigate the best explanation for what we read in Galatians 1:19. See previous posts where those questions are asked.



  • Clarke Owens
    2018-07-07 12:59:17 UTC - 12:59 | Permalink

    Fo me, the key point in McGrath’s column was where he says that we only need one piece of evidence that strongly indicates the historicity of Jesus, “and we have it,” he says, so mythicism should vanish. But he doesn’t say what the strong evidence is. Once again (as with other defenders of historicity of JC), he implies that Jesus is comparable to a historical figure (Geo. Washington), insofar as legends arise in connection with both figures. His point seems to be that historicity is not a cumulative point game, but that points of history are to be determined in isolation, one from another. It seems to me, if he were going to play fair, he would tell us what the incontrovertible evidence of historicity is, so that we could make our own judgment about it. Very often, it will be something such as that many people were willing to die for their belief, etc., whereas religious fanatics die all the time for the most absurd ideas.

  • Giuseppe
    2018-07-07 14:41:54 UTC - 14:41 | Permalink

    Hi Neil,

    About Gal 1:19,
    I argue that a good case for the interpolation has to take in consideration the fact that the reason of the strange detail of the absence of the apostles just that day of the first visit of Paul in Jerusalem, is to allude implicitly (behind the apparently ‘innocuous’ reference to the strict connection between James and Jerusalem already then) to the particular fate that will await precisely that James just in Jerusalem : his martyrdom in that city, followed by the fall of the same city.

    And obviously, this clue to the fate of a persecuted James, is put deliberately in opposition and contrast to a Paul who was a persecutor of the Church. So the reader is led to raise by himself a comparison between Paul and James won clearly by the latter.

    So the reasons to consider as interpolation the passages about a Paul persecutor became also reasons to consider interpolation Gal 1:19 insofar one can read in it the fate that will await James.

  • Neil Godfrey
    2018-07-07 20:32:36 UTC - 20:32 | Permalink

    McGrath does not tell his readers in the post we are addressing what he has in mind as the “clear-cut” evidence for the historicity of Jesus but from previous posts and comments I am convinced that it is the “brother of the Lord” passage in Galatians 1:19 that he has in mind. If I am wrong then someone will no doubt inform me.

  • Gary
    2018-07-07 20:43:44 UTC - 20:43 | Permalink


    “Paul is quite emphatic in the epistle to the Galatians that after he had his vision of Jesus and came to believe in him, he did not go to Jerusalem to consult with the apostles (1:15–18). This is an important issue for him because he wants to prove to the Galatians that his gospel message did not come from Jesus’ followers in Jerusalem (the original disciples and the church around them) but from Jesus himself.”

    “The book of Acts, of course, provides its own narrative of Paul’s conversion. In this account, however, Paul does exactly what he claims not to have done in Galatians: after leaving Damascus some days after his conversion, he goes directly to Jerusalem and meets with the apostles (Acts 9:10–30).”

    The conclusions I have to make about Gal 1:19 “but I did not see any other apostle except James the Lord’s brother.”

    1. Acts and Galatians are contradictory.
    2. Galatians is less likely to be true over Acts, in this one issue; did Paul go to Jerusalem immediately (Acts), or did Paul spend 3 years elsewhere, and did not directly interface with Jesus’ disciples or other followers for a long time? If you believe Galatians is more likely true, then you have to believe the information Paul received about Jesus’s teaching, was either from a ghost, or the people Paul himself persecuted. Very unlikely.
    3. The further conclusion you can draw – Galatians 1:19 can certainly not be used to prove anything about the historicity of Jesus, since Gal 1:15-18 is questionable itself.

    • Neil Godfrey
      2018-07-08 07:00:17 UTC - 07:00 | Permalink

      Galatians looks like a letter by Paul in all its parts but a serious historian would not take that appearance at face value; s/he would put it to the test. Similarly, Acts looks like a kind of history of the early church, but again, a serious researcher would not take that appearance at face value. When we study these writings alongside related literature and we find very good reasons for doubting that Paul ever said anything about meeting “the brother of the Lord” and very good reasons for treating Acts as theological fiction composed to meet a political need in the second century.

      I expect apologists to take a biblical text at face value without assessing and testing it against related writings, but not serious critical historians or bible critics.

      • Gary
        2018-07-08 14:36:26 UTC - 14:36 | Permalink

        From the Ehrman site, “If he did stretch the truth on this matter, however, his statement of Galatians—“In what I am writing to you, before God, I do not lie”—takes on new poignancy, for his lie in this case would have been bald-faced. More likely the discrepancy derives from Luke, whose own agenda affected the way he told the tale.“

        This is one time I’d disagree with Ehrman.
        Yes, Acts is written much later. But “More likely the discrepancy derived from Luke”, he is acting like Paul in Galatians didn’t have a motivation. ”“In what I am writing to you, before God, I do not lie”, sounds pretty fishy to me. And it still doesn’t answer the question of where did Paul pick up Jesus’ teachings in the first 3 years after conversion. Out of the blue, ghost, or a bunch of proto Christians in Turkey, who didn’t even know Jesus? Paul had a pretty advanced theology in the beginning, considering no texts existed then, and oral stories were the only source of his theology. He had to have gotten the Jesus teachings from Jerusalem, not Turkey. And he certainly didn’t get the stories from the Christians he persecuted. While persecuting them, I suppose they told Paul, “hey, before you kill me, I want to tell you a story”. 🙂

  • proudfootz
    2018-07-07 20:45:20 UTC - 20:45 | Permalink

    People who want us to believe in the ‘historical Jesus’ often seem to like taking hostages – in this case it is George Washington who is being threatened. Or maybe it’s Boudicca, or Julius Caesar, or Abraham Lincoln.

    What they don’t want anyone to realize is that the arguments for the historical existence of every figure is going to be unique to that person.

  • Neil Godfrey
    2018-07-09 00:09:01 UTC - 00:09 | Permalink

    Richard Carrier has responded to James McGrath’s post: James McGrath Gets Everything Wrong (Again)

    • Clarke Owens
      2018-07-09 12:16:13 UTC - 12:16 | Permalink

      Carrier’s blog mentions this Vridar blog with approval, and makes the interesting claim that “all probability is mathematical,” a topic that might be interesting to discuss here.

      • 2018-07-09 14:01:50 UTC - 14:01 | Permalink

        There is a sense in which quantifiers (e.g., “usually”) and qualifiers (e.g., “proficiently”) both express probability, even though the former are mathematical while the latter are not – both can, for instance, be used to describe student performance and what a letter grade means on an elementary school report card.

      • Gary
        2018-07-09 14:19:50 UTC - 14:19 | Permalink

        That assumes the initial conditions/assumptions are correct. If not, “Garbage in – Garbage out”.

      • Neil Godfrey
        2018-07-10 22:13:34 UTC - 22:13 | Permalink

        I am thinking of addressing his claim that all historical thinking is mathematical. Maybe so at a very high-level of abstraction where I wonder if all reasoning can be said to be ultimately mathematical so that the point becomes mute.

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