Just this month Bible scholar James McGrath, whose incompetence and dishonesty I have documented several times now (example, example, example, example), posted a really foolish attempt to critique Bayesian history on his blog. Titled Jesus Mythicism: Two Truths and a Lie, McGrath aims to expose “the problematic case that” I have “made for incorporating mathematical probability (and more specifically a Bayesian approach) into historical methods.” Here’s why this shows McGrath doesn’t understand logic, math, Bayes’ Theorem, or even history.

Neil Godfrey has already destroyed this over at Vridar. But here’s what I think everyone needs to learn…

History Is Mathematical

Just McGrath’s opening statement alone is far more problematic than anything I’ve argued. McGrath must somehow think there can be some kind of “probability” that isn’t mathematical. But there isn’t. And that’s not something I am “proposing.” It’s an inescapable truth of logic. All statements of probability are mathematical. Period. Therefore all statements about what probably happened in the past are mathematical. By Hypothetical Syllogism, a standard formula of logic: if A, then B; if B, then C; therefore if A, then C. If all historical statements are stating a probability, and if stating a probability is always mathematical, then all historical statements are mathematical.

You can’t get around this. So how could any case “for” the fact that historical conclusions assert what’s probable be “problematic”? Is McGrath a postmodernist who rejects all historical truth? Is he an irrational dogmatist who believes every claim about history is either absolutely false or absolutely true without any probability of it being otherwise? You might see we have a lazy thinker here already. But once we admit all statements about the past are statements of probability (“unlikely,” “most likely,” “very likely,” “almost certainly,” are all making distinctions of probability), then we cannot avoid concluding that all statements about history are mathematical. You cannot escape this by insisting you are not “using numbers.” You are necessarily implying numbers every time you make such assertions…provided you mean by such statements anything at all.

As I explained already to a bunch other Doofuses:

We measure uncertainty as margins of error around a probability. If you say “I think x is very probable,” you cannot mean the probability of x is 20%, which is actually improbable, nor 60%, as that is probable, but hardly “very” probable; it’s surely not the kind of probability you mean. So we have the right to ask you what you mean: how far would a probability have to drop to make you no longer refer to it as “very” probable? You can tell us. It’s arbitrary; it’s your own words, so you get to say what you mean. But then you have to be consistent. You can’t start throwing up equivocation fallacies, constantly changing what you mean mid-argument. Unless you’re a liar; or actually want to be illogical. And only a doofus wants to be illogical.

We can then ask you, well, if you mean it has to be, perhaps, at least 90% to qualify for you describing it as “very” probable, what’s the most probable you can mean? When would the probability cease being just “very” probable and become, say, “extremely” probable? Same rules. You have to mean something by these terms. Otherwise they literally mean nothing. If you mean the same thing by “merely” and “very” and “extremely,” then those words convey nothing anymore. But the only thing they could ever mean differently, is a different range of probability. There is no escaping this.

So when this doofus tries to claim language can operate without any logical coherence in probability theory, he’s just being a full doofus.

So has McGrath joined the doofuses?

Once you admit all probability statements are mathematical, you need then to ascertain what mathematical formula describes what you are doing when you make assertions about probability. What are historians doing when they reach conclusions about what is or isn’t probable, or how probable it is? The answer will always be Bayes’ Theorem. There is no avoiding that. No one has proposed any other. And no other known to me, accurately describes any valid historical reasoning—unless it just reduces to Bayes’ Theorem again. This has been independently verified, under peer review, by a philosopher of history; and a philosopher of archaeology (and by several archaeologists as well, cited thereby). So it’s apparently Bayes’ Theorem all the way down. Historians therefore had better start learning this. Otherwise, as David Hackett Fisher has extensively documented, they will be highly prone to logical error in their work.

Indeed, I even demonstrate by syllogistic logic that all historical claims are necessarily Bayesian in Proving History, pp. 106-14 (which, incidentally, was formally peer reviewed by a professor of mathematics and a professor of Biblical studies—as I insisted on in my contract with the publisher). I likewise show there that all standard historical methods usually employed (as loose logical formulas), are in fact actually Bayesian (Ibid., Chapters 4 and 5). Does McGrath interact with or critique any of these demonstrations in Proving History? Nope. He didn’t even do that when he claimed to have read the book. That by itself is already incompetent. Competent academics, actually read a book they critique, and actually interact with its arguments. So why won’t McGrath do that? That he doesn’t, entirely discredits his opinion in the matter. Why he doesn’t, we can only guess.

McGrath cannot deny history is mathematical. Because he cannot deny it is probabilistic. And he cannot deny all assertions of probability are mathematical. So if what he wishes to object to is instead only the specific formula, then the burden is on him to present what mathematical formula describes correct historical reasoning. If he cannot, then what remains is what has been proved under peer review: that it’s Bayes’ Theorem. He cannot logically gainsay that, if he cannot even comprehend it. He would do better to just admit he doesn’t understand the logic of probability; and admit this is a serious problem for a guy whose profession is all about making assertions of probability. Otherwise, he has a job to do.

What Bayes’ Theorem Actually Says about Historical Reasoning

McGrath claims that “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.” That’s entirely false. Thus demonstrating McGrath does not understand Bayes’ Theorem. Even after supposedly reading a whole book about it and presumably studying it as any competent critic would do.

Neither I have said nor does Bayes’ Theorem ever entail “each bit of evidence that is compatible with” some theory h being false “diminishes” the probability of h. To the contrary, one of the principal insights of Bayesian reasoning is that such evidence has no effect at all on the probability of h. Merely “being compatible” with a conclusion, only increases the probability of that conclusion if that same evidence is incompatible with the alternative (to some degree). Otherwise, an item of evidence can be equally compatible with both h and ~h, in which case it has no effect on the probability of h. The likelihood ratio is then just 1/1, which is just 1, and anything multiplied by 1 is itself. No change. I discuss this fact repeatedly in Proving History. It is impossible McGrath can have missed it. Unless he never really read the book.

Likewise, “each bit of evidence of untruth would diminish the evidence for truth” is only true if you more carefully reword that to say “each bit of evidence that is more probable on the untruth of h would diminish the probability of the truth of h.” Which is simply a straightforward description of evidence. That’s what evidence does, and what something must do to be called evidence for one conclusion or another. It is the likelihood ratio that determines whether any e is evidence for or against h, and how much for or against h it is. Hence if a made-up legend about someone is just as expected whether they existed or not, then that made-up legend argues for neither conclusion.

It is frequently the case that there is evidence against h that is weak (e.g. O.J. Simpson insists he is innocent), but evidence for h that is strong (e.g. a ton of forensics and the complete lack of any plausible alternative). The conclusion then is h is probable. But it would be even more probable without that contrary evidence (e.g. if O.J. Simpson admitted he was guilty). That h can already be almost certainly true (e.g. 99% likely) and yet could still be even more probable (e.g. 99.99% likely) is a simple mathematical fact that shouldn’t be confusing or freaking out anyone who even so much as graduated middle school.

So once we have those two 6th grade math-facts cleared up, let’s look at the pile of poo McGrath’s confusion has tripped him into:

But in history as historians practice it, each claim, each piece of evidence, stands or falls on its own merits. The non-historicity of the cherry tree incident in no way dilutes the case for the historicity of George Washington. There is no need to go back over the evidence and do a recalculation of the case for historicity. That is not just because the impact of that non-historical story is infinitesimally small in comparison with other evidence. It is that the case for historicity is based on the evidence which supports it, and is not diminished by the fact that all famous people also have non-historical claims made about them.

Here McGrath seems to think that somewhere I have said that simply because there are false things said about Jesus, that this reduces the probability of Jesus. Holy balls. Dude. I said exactly the opposite! And have repeatedly said exactly the opposite. For example, here is the actual conclusion with respect to the Gospels in my peer reviewed case for the non-existence of Jesus (which McGrath has also lied about reading):

The Gospels generally afford us no evidence whatever for discerning a historical Jesus. Because of their extensive use of fabrication and literary invention and their placing of other goals far ahead of what we regard as ‘historical truth’, we cannot know if anything in them has any historical basis … This is equally expected on both minimal historicity and minimal mythicism, however, and therefore (apart from what we’ve already accounted for in determining the prior probability in Chapter 6) the Gospels have no effect on the probability that Jesus existed, neither to raise or lower it. (pp. 506-07)

Neither to raise or lower it. So why does McGrath believe I said each of these false stories “lowers” the probability of history? Because he is incompetent. And a liar. He did not read my books, despite claiming to. He consequently doesn’t know what’s in them. He chooses to make completely false claims about what’s in them instead. Why does historicity have to be defended with incompetence and lies? That’s what more and more people want to know.

Now, I did say “apart from what we’ve already accounted for in determining the prior probability.” So there is some sense in which I claim the evidence of the Gospels argues against the historicity of Jesus. But what sense exactly is that? Is it, as McGrath here falsely implies, that I am adding up false story after false story and concluding each false story reduces the probability of Jesus? Absolutely not. Explicitly not. And any honest person who actually read my work knows this. To the contrary, I have argued on this blog that more evidence of Jesus’s mythification probably couldn’t further reduce the historicity of Jesus. Because once you are that mythical, there is no more mythical you can be. Or to be more precise, there is no more evidence in our background as to the frequency of persons that mythologized, being mythical.

The Gospels only tell us, not on an item-by-item basis, but globally, how mythologized Jesus was. The answer: just as mythologized as a lot of other mythical people. In fact, few historical persons were ever that mythologized. I’ve explained this to McGrath before. If you put Jesus and everyone else as mythologized as he is into a hat, and drew one out at random, the odds you’d draw a historical person are no better than 1 in 3—and possibly as bad as 1 in 15 (OHJ, Ch. 6). Because this cannot be circularly prejudged—so we cannot say in advance whether the person drawn out of that hat is Jesus or not. The odds must be the same. For Jesus as for anyone else in the hat. That can only be changed with evidence—that is, evidence specifically that Jesus is more likely historical than the others in that hat. Notably, exactly what McGrath wants to say.

For instance, if for some reason Julius Caesar were in that hat (he isn’t, but let’s pretend he is), the prior odds he’d be historical would be 1 in 3—the odds upon merely drawing his name from the hat—but the evidence would still be overwhelming that he nevertheless existed, totally crushing that 3 to 1 against into millions to one in favor. So we need evidence. And that’s what we lack for Jesus. Despite McGrath’s hyperbolic assertions to the contrary, we have no evidence for Jesus that can even be called good…compared to every other person we are certain existed. For example, even Hannibal or Spartacus are way better attested.

This means, for example, the Argument from Contamination only pertains to the prior, not the posterior…provided there is evidence of a thing other than mythical texts about it; if there isn’t, the prior is all you are left with. But this is why McGrath needs to learn to tell the difference between a prior probability and a posterior probability. He needs to learn how frequencies work within reference classes. He needs to learn how to correctly class a figure like Jesus. And he needs to learn how evidence works—namely, why evidence increases or decreases a probability, and how much. And when it has no effect at all. Otherwise, McGrath can have no real idea of what he is even doing when judging probabilities.

Epilogue

I’ve covered this before. And again. In very easy terms. And I explain it in detail in OHJ (e.g. pp. 506-09, 451-52, 601-06). McGrath has no excuse at this point. History is all about ascertaining probabilities. Learning how probability works is his job. So McGrath needs to do his damned job, and finally, actually, learn how probability works. Until he does, he can’t ever claim to have a logically valid argument for any conclusion. Including whether Jesus existed.

 

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