Possibiliter Ergo Probabiliter and the McGrew Nativity Debate

Possibiliter Ergo Probabiliter and the McGrew Nativity Debate December 20, 2020

Possibiliter ergo probabiliter is a fallacy that Richard Carrier coined to express the ubiquitous technique that theists use to try to explain away issues that pop up in the Bible and this is no more evident in Christian approaches to defending problems within the infancy narratives of Luke and Matthew. Indeed, in my recent debate with Lydia McGrew, this was on show in no small measure. I spent some time at the beginning of the debate warning of this and, it seems, for good reason.

This fallacy means, essentially, that some explanation for events is possible, and, therefore, it’s probable, and, therefore, it’s what happened. What this means is that any conceptually possible explanation can be plugged into the formula and be seen to be explanatory plausible and then probable. The jump from possible to plausible to probable to being the best explanation is a tremendously problematic thing, but it, unfortunately, represents McGrew’s case very well, as well as most of the Christians discussing the debate on particularly the Unbelievable? YouTube video forum. I think there is an interesting use of the word “plausible” from McGrew that has a casual meaning – that an explanation can be seen as a prima facie “normal” thing to happen. More on this later.

Here are some examples of a few comments.

From New Zealand Christian philosopher Glenn Peoples:

Jonathan is seriously misunderstanding or misusing the idea of “possible therefore probable.” He raises objections as though they show that events (eg the census described in Luke) did not happen. In order to show that this refutation fails, one need only show that there is nothing about the event that indicates that it couldn’t have. They don’t have to create anything like a conclusive case that it did. In order to be a good objection, it is up to Jonathan to show that the Gospel claim is untrue or at least very unlikely.

I replied: You misunderstand my position. What you arguing for has the same epistemic value as arguing the aliens came down and did it. This is conceptually possible but has no positive evidence nor any inductive basis to give it a prior probability. something like a census in 8 or 9 BC under a client kingdom has Quirinius ruling twice, then the cogovernor and the census taking place in a quiet kingdom. All three of these have no precedent in Roman history. This is what Lydia is arguing for Anns I would say almost certainly didn’t happen because, though it is conceptually possible, it is not in the slightest probable all, depending on how you define possible, possible in terms of Roman custom and procedure.

He replied:

No, I understand your remark about “possible therefore probable” perfectly well. You accuse apologists of appealing to a scenario that is merely possible, illegitimately treating it like it is probable. And you’re entirely wrong to make the alien comparison. Remember, Jonathan, what you thought you had offered re: the census was framed as a defeater: an argument that purported to show why the Gospel accounts cannot be true. But such a defeater fails just if there is any number of reasonable possibilities that could fend of the defeater. And clearly there are. Nobody is obliged to demonstrate which scenario is true, the point is, you don’t have a defeater after all. You just don’t know how this works, and “possible therefore probable,” in Latin no less, was merely a rhetorical flourish.

I said: I have to completely disagree with you because your notion of what are reasonable Possibilities is entirely problematic. This is entirely my point. You are positing things that are conceptually possible such as a co–governorship of Quirinius, a census in acquiring kingdom, or the double ruling of Quirinius and so on. The problem is, though these are conceptually possible, such as aliens doing something, this is customarily and historically unprecedented and therefore entirely improbable. It is not just about positing a “reasonable possibility” when all this means is something that doesn’t break the rules of natural law. Inductively, you are in a hiding to nothing.

He stated:

Yes, you do have to disagree, but not for any good reason. You are misrepresenting those possibilities by saying that they are mere;y “conceptually possible.” Nobody believes that, not even you. Not only are they conceptually possible, but they are the sorts of things that actually happen. Do you know of any alien visitations? So your argument turns on your claim that there just is no plausible explanation of what Luke and Matthew both say about the census, and when people point out that there are plausible explanations after all, your comeback is that this doesn’t show they happened. So it’s a failed critique of the Gospels. (Feel free to comment on this for the benefit of others, but I’ll leave it there.)

To which I simply obliged by pointing people to my recent article on this: Nativity, Census, Quirinius: Refuting Very Poor Christian Apologetics Again. Even More.

And then the rather unsavoury Matthew Firth chipped in with:

What a silly argument. We have no evidence of aliens, thus any recourse to aliens is dubious. But we do have evidence for a lustrum census in Judea in 8/9BC, so recourse to the idea of a census during the final couple of years of Herod’s reign is perfectly sensible.

To which, I replied: Ha, brilliant. We actually have more evidence of aliens than 1) A Roman provincial governor co-governing ever in Roman history 2) A Roman provincial governor ruling twice ever in Roman history 3) A client kingdom having a Roman-decreed census ever in Roman history 4) explicit evidence of a census in Judea under Herod 5) explicit evidence of 1) and 2) happening with Quirinius.

Oh dear, Firth, you have really shot yourself in the foot there! D’oh!

Lydia McGrew on another thread stated:

Just a really quick probabilistic point, btw: It simply isn’t true that I’m saying that if something is possible, it is probable. That’s a misunderstanding. What needs to be probable is the disjunction–this or this or this. I am saying that the possiblities I’m raising are reasonably *plausible*, and frankly, I think people can see this by common sense. And a disjunction of reasonably plausible possibilities is reasonably regarded as probable. Saying something in Latin (possibiliter ergo probabiliter) really doesn’t make one’s criticism stronger! :-)

I said: Hi Lydia. Thanks for this. I would challenge the claim “the possiblities I’m raising are reasonably *plausible*”. Saying possibiliter ergo probabiliter is shorthand for having to explain it every time, but when I first use it, as the name of the fallacy, it is good manners to explain it! How would you explain the 10-12 year gap in a plausible/probable manner?

McGrew replied:

I’m not sure what you mean by the 10-12 year gap, but I strongly deny that Luke is saying that Jesus’ birth occurred during the 6 A.D. census. In fact, of all the interpretations of what he is saying, that is probably one of the most improbable*, since it would contradict multiple things that he himself says and reports elsewhere (such as that John the Baptist was conceived in the reign of Herod the Great), both in Luke and in Acts. It’s obvious that he isn’t saying *that*. If he’s made a mistake at all, it may be in thinking that Quirinius was governor twice, perhaps through confusing “Quirinius” and “Quinctilius,” but that would just be an example of his sincerity in believing that a census took place at the time of Jesus’ birth–an earlier census in Judea. I realize that you have a bunch of other objections to the actuality of such a census, and I was not (and am not) planning on a Youtube combox exchange with you about that. (In fact, I have a video and blog post of my own on the census coming out on Sunday.) But the point is that Luke definitely does not *mean to say that Jesus was born during the census in the year that we would call 6 A.D. That’s not even just a matter of plausibility. That’s pretty well definite. An example of a reasonably plausible theory (that I had in mind) would be the conjecture that Joseph had a familial home in Bethlehem or some property there requiring him to register.

My reply: So, IIRC, you somehow dismissed the Quirinius census of 6 CE by saying there was one in 8/9 BCE. This could have been a debate in itself. Can you establish what this “lustrum” census of the time was, in Judea, and why it was a Roman decreed census in a client kingdom? This is a punt to an implausible not-even possibility afaict.

And her final point:

Now, look: I already said that I’m not going to have a big debate on all the census issues here in the combox. But that isn’t why I say that Luke is not talking about the 6 A.D. census. I say that for the other reasons I’ve given about what else Luke says and what he knows. Whatever else you may say about whether Luke was mistaken or not, he clearly intends to be talking about some other census. I don’t know how to get across this interpretive point more clearly. Luke has numerous references to other historical information that shows that he knows that Jesus wasn’t born in the year 6 A.D. Merely as a matter of interpreting his own statements in the context of his own writings, we can see that he isn’t trying to say that Jesus was born during that census. I think I’ve made myself clear enough on this limited point, so I’ll leave it at that. And my original purpose in coming in here was to clarify that I am not saying that a merely possible hypothesis is therefore probable–that’s a misunderstanding of what I have argued at any point, ever.

The problem here, without opening a can of worms about John the Baptist (I may make a separate article on that) is the claim of a census earlier in 8/9 BCE. If we grant a thesis that I’m not sure that McGrew adheres to, but at least she offers, that Luke got Quirinius wrong, we still have a census in a client kingdom of Judea in 8/9 BCE under Herod and that this required Joseph to return to his ancestral home. For Lydia to claim that Joseph could have had property in Bethlehem and that’s why he returned to Bethlehem for a census, we still have issues:

  1. This was a client kingdom, and there is no evidence of a Roman-decreed census ever having happened in a client kingdom (an autonomous buffer zone on the edge of the Roman Empire).
  2. There is no evidence of this happening under Herod, a very well-documented king.
  3. This seems too early for Jesus’ birth.
  4. It would not require Mary to attend.
  5. Luke clearly says: “So Joseph also went up from the town of Nazareth in Galilee to Judea, to Bethlehem the town of David, because he belonged to the house and line of David.” So this is getting registered in Bethlehem not because he has property there, but because he is of David’s ancestral line.
  6. Any rationale for a census requiring people to return to their ancestral homes is thoroughly implausible. I have yet to hear anyone give even a remotely plausible explanation as to why this requirement might exist. It has not been seen anywhere in the history of censuses.

And so on. Indeed, this is an incredibly implausible scenario, whichever way you cook it. McGrew claims that her harmonisation is not an example of positing something implausible, claiming it is reasonable and plausible, but this is simply not the case. She would have to bend the probabilities and inductive observations we have of Roman history and censuses in order to take her attempts seriously.

That a tekton might have property in Bethlehem is perhaps somewhat plausible, but for this to require him and his partner to travel to a different tax area to register, even though Luke claims it is for ancestral reasons, is what takes this to punting to the conceptually possible whilst ignoring the probable (that one or both of the Gospels are wrong). This is an example of that use of “plausible” I was mentioning earlier. Here, it seems a prior “plausible” that a Jewish tekton might have a second property. As such, you might think the whole explanation is plausible. But there is an awful lot more work that “owning a second property” has to do to become really plausible qua probable (that of 1-6 above). Don’t get drawn in by a seemingly simple plausibility that actually hides an awful lot of low probability implications.

Of a Herodian census, Richard Carrier states:

Was it a Census Conducted by Herod the Great?

One might try to argue that the census was actually not Roman at all, but conducted by Herod. Of course, this is prima facie implausible, for it is most strange that Luke would not simply say this, but instead associate it with a Roman governor and an Imperial decree: the plain language and obvious context leaves no reasonable interpretation but that Luke meant a Roman census (and again, the possibility that Luke is drawing on Josephus would support this). Even if some other nations held their own censuses, the Jews held a negative attitude toward taking a census in peacetime.[16.1] Had Herod conducted such a census on his own initiative, it would have been a truly remarkable event, and could not have escaped mention by historians such as Josephus. And Herod the Great enjoyed the greatest favor and freedom of any client king ever under Roman influence, so any Roman attempt to “force” Herod to run a census would have been even more inexplicable and unprecedented….

The bottom line is that there is no evidence of a Herodian census, and no reason to believe there ever was one. And even if there were, there is no way Luke’s reference could be to such a census, and thus [the] argument is baseless.

In conclusion, not just on this point, but certainly at least on this point, McGrew and other Christians are deferring to the possibiliter ergo probabiliter fallacy and I think the jump is epistemically problematic. .

[Please grab a copy of my book on the Nativity (The Nativity: A Critical Examination) [UK].]

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