Bart Ehrman, multiple attestation and probability

I've just listened to the entire 12 hour audio book of Bart Ehrman's "Did Jesus Exist?" which someone posted on YouTube. I transferred it to my iPod, and listened to it while commuting, of course.

I don't have too much to say about the book. I totally understand why many folks in the "Mythicist" camp are angry at this book, as it does seek not only to counter their arguments, but also makes a number of ad hominem attacks on them, individually, specifically, by name. But I'm not going to defend them here, they've gone as far as to write a whole book in response. I might read that eventually, but I'm in no hurry...

I also don't dispute the central thesis of this book. I'm reasonably convinced that there really was a 'historical Jesus' and that Christianity, at least in part, is based on some of his teachings and actions. I also believe, as explained in this book, that an awful lot of legends have been added to the historical core of Christianity, such that the modern religion is almost certainly something that the 'historical Jesus' wouldn't recognise at all.

But the main thing that annoyed me with Ehrman's book was the sloppy thinking at the centre of his reasoning. During his ad hominem attacks on the mythicists, he made a big deal about the fact that most mythicists (with the exception of Robert M. Price and Richard Carrier) do not have postgraduate degrees in relevant disciplines, and so (in his thinking) the arguments by these people can be largely dismissed. For Ehrman, appropriate qualifications are essential. It is odd, therefore, when he wades into the field of probability - something that he has no postgraduate education in - and bases the main points of his argument on probability judgements. He does not appear to understand how probability works.

The core of Ehrman's reconstruction of the historical Jesus is based on the criterion of Multiple Attestation - put simply this is taken to mean that if a story about Jesus or a teaching attributed to Jesus is attested in multiple independent sources, then it is more likely to be true or authentic than one which is not. Ehrman builds a library of stories and sayings that are multiply attested and concludes that these are most likely historically authentic.

Hang on, do you see what he did there? He takes a statement of relative probability (that Story A, which is attested in two independent sources, is more likely than Story B, which is found in only one source), and assumes it to be a statement of absolute probability. In other words, he seems to equate "more likely than" with "certainly happened". This is very sloppy thinking! An event that has a one in a thousand chance of having happened is more likely than an event which has a one in a million chance of having happened - a thousand times more likely in fact - but both events are still extremely unlikely. Relative probability tells us nothing without some quantification of absolute probability. Just because a story appears in multiple sources, doesn't mean it actually happened. It merely means that more people wrote it down.

Another annoying aspect of Ehrman's reasoning is the way he invents independent sources. I actually can't remember all the sources he claims, but his list of independent sources includes:

Mark; Q; M; L; John; Traditions in Paul; Traditions in Acts; Traditions in non-Pauline epistles; Revelation; and various non-scriptural sources.

This is all very impressive, but Ehrman forgets that Q is a scholarly construct which may or may not have existed. If it did exist, then the claim is that both Matthew and Luke used some of it, in addition to Mark, when creating their own gospels. There is no claim that both of them used all of Q in their gospels, so it seems quite likely that one or both of them might have missed out bits of Q. This means that it is possible that some, if not all, of the M and L material was actually part of Q. In other words it is quite possible that Q, M and L are not independent. Given that this is a real possibility, which we cannot discount, we cannot claim that these are independent sources.

For what its worth, I'm reasonably convinced by the Farrer hypothesis, that Luke used Matthew and Mark when writing his gospel. In this way of thinking, M and Q are reduced to a single source, and Luke (including L?) is not independent of either of them.

How Ehrman manages to justify to himself that the traditions in Acts are independent of L is a mystery to me. Both were written by the same author, it is supposed. And under the Farrer hypothesis, these become not independent from Mark and Matthew.

So I think Ehrman completely overstates his case. Sure there are some stories that are genuinely multiply attested, but not half as many as Ehrman makes out.

While I basically agree with Ehrman's conclusions, I think his overly exaggerated claims of authenticity don't do his case much good. The same case could be built on more sober and reliable reasoning.