Showing posts with label probability. Show all posts
Showing posts with label probability. Show all posts

Thursday, May 16, 2019

The power of storytelling, and the problem of probability.

I’ve recently listened to the debate between Michael Shermer (skeptic) and Luuk Vandeweghe (Christian apologist) which took place in Sequim, Washington, USA, in March 2019, and was broadcast on the Unbelievable radio show and podcast a couple of weeks later.

It was a debate on biblical miracles, in front of a mostly Christian audience. It's fair to say that Vandeweghe won the debate. But I don't think he won the debate because he is right and has the facts on his side, I think he won the debate because he's a great storyteller, and told a compelling story of early Christianity which sounded entirely plausible, and therefore believable. Shermer never got the chance to take the story apart, and so wasn't able to counter the power of a good story.


Christians have always had great storytellers and great stories. But just because they have great stories, perhaps even the greatest story ever told, doesn't make the stories true. Sometimes fiction is more interesting than real life.


So let's break down Luuk Vandeweghe's story and see if it holds up to scrutiny. Obviously I'll only comment on a few aspects of it here, but I'll try and give the gist of the whole and be accurate in a few direct quotes.


He began by acknowledging that he was telling a story: "I want to tell you a story..." and used a repeated refrain to link together all the different characters he told us about: "They weren't liars and they weren't fooled".


He started his story in 66AD with a story about the emperor Nero in Rome, told by Tacitus. Vandeweghe doesn't tell us that Tacitus was only ten years old in 66AD, and wasn't there, and wouldn't write this account until at least 30 years later, he implied an accurate report of the events in AD66. He told how Nero took Christians, nailed them to crosses, and burned them as torches for his garden parties. He then told a tale of someone at the Colosseum, who could have saved their family members from being torn apart by wild animals if only they had denied Christ, but who chose to stay faithful. He said: "Tacitus tells us Christians gained the sympathy of the people because they never did this, they suffered, they endured, and they won over the hearts of Rome during that era, because they never went back on their testimony".


The problem I have with this, is that Tacitus says no such thing. Tacitus does not recount the story of the people at the Colosseum being given the opportunity to deny Christ and live. As far as I know, those stories come from 2nd century writings like the Apocryphal Acts, and writings like the Epistles of Ignatius, it's not in Tacitus. And the 2nd century writings contain a lot of stories that serious historians laugh at. They are not history. But here, a storytelling Christian has merged aspects of real history, with some ambiguous interpretation, with probably fictional stories, to make the story he wants to tell. This is not history, this is apologetics, and if the truth has to be bent along the way, so be it.

The storyteller told a good story, does it matter that it is probably not true? 


Is Luuk Vandeweghe a liar, or has he been fooled?

Here's what Tacitus actually said:
"Consequently, to get rid of the report [that Nero had ordered the fire in Rome], Nero fastened the guilt and inflicted the most exquisite tortures on a class hated for their abominations, called Christians by the populace. Christus, from whom the name had its origin, suffered the extreme penalty during the reign of Tiberius at the hands of one of our procurators, Pontius Pilatus, and a most mischievous superstition, thus checked for the moment, again broke out not only in Judaea, the first source of the evil, but even in Rome, where all things hideous and shameful from every part of the world find their centre and become popular. Accordingly, an arrest was first made of all who pleaded guilty; then, upon their information, an immense multitude was convicted, not so much of the crime of firing the city, as of hatred against mankind. Mockery of every sort was added to their deaths. Covered with the skins of beasts, they were torn by dogs and perished, or were nailed to crosses, or were doomed to the flames and burnt, to serve as a nightly illumination, when daylight had expired. Nero offered his gardens for the spectacle, and was exhibiting a show in the circus, while he mingled with the people in the dress of a charioteer or stood aloft on a car. Hence, even for criminals who deserved extreme and exemplary punishment, there arose a feeling of compassion; for it was not, as it seemed, for the public good, but to glut one man's cruelty, that they were being destroyed."
This does say that Nero blamed the fire of Rome on Christians, and had some Christians crucified, some burned as torches, and some torn by beasts. It doesn't say that any of them were given the option to deny Christ and be saved. And while it does say that the people of Rome had some compassion for the Christians, it doesn't say that this was because they were faithful to their beliefs.

Luuk made the claim that "the early martyrs weren't liars", but on the evidence of Tacitus, we don't actually know what the early martyrs said. They pleaded guilty to something, but Tacitus is unclear on what. Possibly the crime of setting fire to the city?



But the storyteller told a good story, does it matter that it is probably not true? 


Is Luuk Vandeweghe a liar, or has he been fooled?


The apologist's story now goes a couple of years before AD66 to the supposed martyrdom of Peter. Here, the apologist does that usual apologetic trick of overstating his case: "According to all the earliest sources that we have, Peter is the man who inspired Mark to write his gospel". Really? All the earliest sources? Paul doesn't say it, Acts doesn't say it, even Mark doesn't say it, secular historians like Tacitus and Josephus certainly don't mention it. In fact, most of the earliest sources we have do not mention the gospel of Mark or any connection between it and Peter. I think our earliest source on the supposed link between the two is Papias in the early to mid 2nd century. And there are reasons to question whether the writings Papias was talking about are actually the same thing as the book we now call Mark. And quite a few historians question the reliability of Papias. Most of the claims we have for a link between Peter and Mark are late 2nd century, possibly a whole century after the death of Peter, certainly more than a century after the death of Jesus. Yet the apologist declares, with apparent certainty, that the miracles in Mark came from the eyewitness accounts of Peter and that he died for his belief in those miracles.


I'd like to insert a little parenthesis here about probability. I'll continue with Luuk's story in a minute.

Here our apologist made three historical assertions in quick succession. These are:

  1. Peter witnessed the miracles of Jesus.
  2. Peter told the stories to Mark who wrote them down.
  3. Peter died because he would not abandon his belief in these miracles.
For the overall story to be true, all three of these need to be true. If one is false, the whole story is proven false. But historical reconstruction doesn't work in absolute truths, it works in probabilities.  The way probabilities work is that the probability of the whole is found by multiplying the probabilities of the individual components together. That is Ptotal = P1 × P2 × P3.

Suppose you think there is an 80% probability that each of these three statements is true, the probability of the overall story would be 0.8 × 0.8 × 0.8 = 0.51 or 51%. That's not a statement of high certainty, is it? But suppose we doubt the stories of Papius and think that it is unlikely that Mark's stories come from Peter, perhaps allocating that a 20% chance, and we think there's only a 50% that Peter actually saw miracles, and we think there's only a 30% chance that he would not have been martyred if he had changed his story, then we get 0.2 × 0.5 × 0.3 = 0.03 or only a 3% chance that the overall story is true!

In order for you to have (say) a 75% (or higher) probability in the overall claim, you actually need at least a 90% certainty in each of the three claims. Few historians would be likely to stake their claims that high.

This is what happens when there are only three claims being combined, Luuk's overall story has many more claims. If even a few of these have low probability, the likelihood of the overall story becomes very small. However, this reasonable application of probability in history is completely masked by compelling storytelling. A good story makes something plausible sound like something probable. They are very far from being the same thing. I'll try the sum at the end of this post... but now back to the story. 



Luuk now makes something entirely up. He says to imagine the evangelist Luke in the crowd, watching the crucifixion of Peter. Where did that come from? I've never heard that claim before. It would sure help the apologist's case if the author of Acts was there at the events he describes in his book, or the events he alludes to, because -of course- the martyrdom of Peter is not actually recorded in Acts. If Luke was there and if he witnessed Peter not denying Christ and being crucified as a consequence, and if he wrote that in his book, that would indeed be good evidence. But the thing is, this didn't happen, he didn't see it, he didn't write it. This part of the story is a complete red herring.


But the storyteller told a good story, does it matter that it is probably not true? 


Is Luuk Vandeweghe a liar, or has he been fooled?

Although the chain of evidence Vandeweghe is trying to build has already been broken with the lie above, he carries on and makes a big deal of the historical reliability of Luke's writings. He portrays Luke as a top notch historian who interviewed named eyewitnesses, including Mary the mother of Jesus. He claims that every time a minor character is named, this is probably because Luke has interviewed the eyewitness in question, and has told their story. It makes a great story, but this is also a highly doubtful claim. Nothing in there can be stated with certainty.


Scholars have long known that Luke used Mark as his primary source, but freely changed the bits he didn't like and added in other stories to bulk out his gospel. While the opening statement of Luke's gospel does sound like a claim of historical scholarship, not everyone is convinced. Indeed, from all I've read on the subject of Luke (and Acts, for that matter) I am reasonably convinced that the final edition of Luke, including the dedication to Theophilus, is a 2nd century expansion of an earlier gospel that made no claim to scholarship. Look at the first couple of chapters of Luke compared to most of the rest of the gospel, they're not even the same genre; chapters 1 and 2 are a musical! If you start reading Luke's gospel at chapter 3, it reads like the start of a book. I think chapter 3 is where the original gospel began and chapters 1 and 2 were added on by whoever was compiling this book for Theophilus. If the compiler was someone called Luke, this can't have been the same character who Paul named in his letters a couple of generations earlier. The apologetic as to why the evangelist Luke was the same as the companion of Paul is quite convoluted and there are good counter-arguments. Its certainly a low probability claim, not a certainty. Yet Vandeweghe relies on Luke's 'unbroken line of evidence' to support his case.


The storyteller told a good story, does it matter that it is probably not true? 


Is Luuk Vandeweghe a liar, or has he been fooled?

The chain of evidence now jumps to an individual I have thought a lot about recently, James the Just, the alleged brother of Jesus. Luuk invokes Josephus at this point. As with Tacitus, Josephus was a child at the time of the events of interest occurred, and was not there to witness them. There is also suspicion that the works of Josephus have been edited by later Christian redactors. Certainly the 'Testimonium Flavianum' has evidence of someone tampering with the text, and if it wasn't for the words 'the brother of Jesus, who was called Christ' in the passage about James, there would be nothing about the story in Josephus for us to think that James was martyred for anything to do with the Christian faith. He was executed as a lawbreaker. Maybe he was just a lawbreaker who was executed, and who has accrued legends after his death. People considered to be martyrs do seem to attract stories of great deeds and holiness.


Luuk repeats the oft-told apologetic about how James was a skeptic and became a believer and became leader of the early church. Having invested a lot of time reading up on this and thinking about it, I am really not convinced that this is in any way historical. I think that James the Just was co-opted by the 2nd century church as one of 'their' early martyrs and turned into Jesus's brother in the stories. See my blog post about that here. For me, this is a really weak link in the story.


Once again Vandeweghe repeats the completely non-historical claim that James only had to do one thing to avoid being martyred, he had to deny Jesus. This statement has no basis in history. At best it is simply assuming a detail of one story fits into another story, at worst it is pure fiction.



But the storyteller told a good story, does it matter that it is probably not true? 


Is Luuk Vandeweghe a liar, or has he been fooled?

The apologist next made the claim that the Sanhedrin who killed James were the same group of people who killed Jesus. Maybe they were, maybe they weren't. Given the years that separate the two events, death of Jesus around 30 CE, death of James around 69 CE, it is unlikely that the group members would be the same, and even if one or two were the same, the chance that they would connect the two events in any way is tiny.

Vandeweghe concluded his story by invoking the words of the Babylonian Talmud, a book written between 500 and 600 CE. He described how the Talmud referred to Jesus as 'a sorcerer', and claimed that this belief "went right back" to the trial of Jesus. His point being that by using the word translated here as 'sorcerer' the Jews were acknowledging that Jesus actually performed magic. This is not the word for a trickster, this is the word for the real deal. In other words, the accusers of Jesus believed his miracles were real, even if they believed they were of diabolic origin.


And so, by following a chain of 'evidence' from 66 CE back to Jesus himself, the apologist concluded his case that the miracles of Jesus were real, because the Sanhedrin at the time believed they were real. It was a strong story. The fact that it is not based in history is irrelevant. Vandeweghe won the debate.


But, of course, there is no chain of evidence linking the Sanhedrin in Jesus's day with a book written about 5 centuries later. And even if there was, there are a few details in the Talmud that should give us pause for thought. The Talmud story of "Yeshu the sorcerer" names his five disciples, tried with him, as "Matai, Nekai, Netzer, Buni, and Todah". None of those names feature in the gospel accounts. And in the gospels, Jesus is tried alone, not with his disciples. Maybe Yeshu the sorcerer and Jesus of Nazareth are not the same character? If that's the case, then the apologetic case fails. The dates also do not line up. If you look at the Talmudic timeline, then Yeshua the sorcerer lived and died a generation or so after Jesus supposedly did.


The storyteller told a good story, does it matter that it is probably not true? 


Is Luuk Vandeweghe a liar, or has he been fooled?

I don't think Vandeweghe is a liar. I just think he fundamentally believes the Christian story, and so lines up a bunch of historical data in a way that is coherent with the thing he believes anyway. He's doing good apologetics and bad history. He's been fooled.




So, how unlikely is his story? Here is a list of the links in his story, together with my estimates of probability for each of them. Assuming they are all required to prove the case, and therefore the probabilities multiply together, I'll do the sum and see just how probable or improbable I think the story is... I'll not allocate anything a zero probability as that messes with the calculations.
  • Christians in the time of Nero were martyred for being Christians. (60-95% likely)
  • They could have saved themselves by denying Christ. (20-50%)
  • Peter witnessed the miracles of Jesus. (10-90%)
  • Peter told the stories to Mark who wrote them down. (20-60%)
  • Peter died because he would not abandon his belief in these miracles. (20-80%)
  • Luke witnessed the martyrdom of Peter. (5-10%)
  • Luke interviewed the people who knew Jesus. (10-50%)
  • James the Just was the brother of Jesus. (5-95%)
  • James was martyred because he was a Christian. (5-50%)
  • James could have saved himself if he'd denied Jesus. (20-50%)
  • The same people who killed James killed Jesus. (5-30%)
  • The Talmud story of Yeshua the sorcerer is about Jesus. (10-60%)
  • The Talmud story goes back to the time of Jesus. (5-20%)
  • The Sanhedrin believed that Jesus could do miracles. (5-70%)
Here I've given reasonable ranges of probability from typically skeptical at the low end (actually, some of these should go way below 5% in that case) to fairly generous credulity at the upper end.

If we do the skeptical sum, we end up with a probability of 1.5 × 10-12%, or 0.0000000000015%. That is about a one in 600 Billion chance of it being true. Not very likely, in other words.

Even if we go to the generous end of the scale, the probability of all of Vandeweghe's story being true is 0.02% or about a 1 in 5000 chance. Still not very likely.


With 14 links here, in order to obtain a probability of more than 50% we need to have more than 95% confidence in all of the links in the chain. If we want the overall probability to be 75% or more, our confidence in each of the 14 links would need to be 98% or higher. Historical probabilities almost never go so high. You basically can't conclude a historical fact on a long chain of cumulative evidence. (Which reminds me that I never completed the 2nd part of my review of Cold Case Christianity... maybe someday...) 


Of course, it is possible that Jesus was real and his miracles were real even if the apologist's story is false or partially false, but that's not the point here. The point here is that you cannot prove something historical by telling stories like this, even though they seem plausible to people who want to believe the story.


Wednesday, August 20, 2014

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.

Monday, July 22, 2013

Proving History?

So I finished reading Richard Carrier's book "Proving History: Bayes's Theorem and the Quest for the Historical Jesus" which I mentioned in the previous post.

A few things to say about Richard Carrier before I make comments on this book in particular:
  1. Carrier is an intelligent guy who thinks things through in greater detail than many people do.
  2. He also comes across as quite arrogant in interviews and in some of the things he writes.
  3. His logic appears to be sound and his conclusions generally appear to be justifiable.
  4. He has a clear idea of who his audience is, and tailors his writings to that specific audience.
Starting with that final point, I don't think I am the audience Carrier is writing to in this book. In many of the books by 'new atheists' which I have read, I've realised that the authors are generally 'preaching to the deconverted', as it were, and are not realistically expecting many believers to be reading their books. 'New atheism' books are aimed to give ammunition to atheists. Of course, the flipside of that is that most apologetics books are aimed at Christians to reinforce their beliefs, and not to try to convince atheists to believe...

So, point number one in this review, I don't think any Christian is going to be swayed by the arguments made in this book, even if they (the arguments, that is) are logical, justified and, indeed, correct. But, of course, this book doesn't really set out to sway anyone with its conclusions about history, the main point of this book is to demonstrate to its (mostly non-mathematically inclined) audience that the mathematical technique of Bayes's Theorem is appropriate in historical investigation, and furthermore is the best method to use in historical investigation. I think the book manages to do that, but as conclusions go, its not a very exciting one. The much more exciting and dramatic conclusion comes in Carrier's next book, which isn't out yet.

As a side note, I'm glad that Carrier settled on consistent use of "Bayes's Theorem" rather than "Bayes Theorem", which I find acceptable, or "Bayes' Theorem", which is clearly not acceptable to anyone who understands grammar. Of course, he abbreviates it to "BT" for most of the book, which gets around the problem of the apostrophe. But anyway...

On the whole, this is not a very interesting book. It has interesting bits in it, and makes some interesting conclusions along the way, but I can't really recommend this to anyone as a good read. I doubt even Carrier thinks this book is particularly interesting, but it probably is required before we get to the meaty stuff in the next book. And therein lies the problem, this is clearly the build up to the much more interesting work which is to follow, and may be required reading to understand that second work, but by itself this is a bit dry.

I guess I should explain what Bayes's Theorem is. Put simply, it is a mathematical method for updating your beliefs in the light of new evidence. As used by Carrier, it is a method of assessing the probability of one or more historical hypotheses by considering one or more pieces of evidence. The method provides a framework for determining whether our confidence in a given belief (hypothesis) should be increased or decreased as new evidence presents itself. (I should note here that I have used Bayes's Theorem in my work for over a decade now, so I am fairly familiar with it, and thus am far from the target audience of this book.)

The point of this book is to convince the reader (who Carrier expects to be a non-mathematically inclined person with an interest in history) that Bayes's Theorem is a sound and justifiable method for coming to historical conclusions. He wants everyone to share this belief. If he gets everyone to share this belief, then everyone will have to accept any historical deduction he makes using Bayes's Theorem. And in the next book (I expect) he will end up using Bayes's Theorem to show that Jesus was not the Son of God and, furthermore, probably didn't exist. But in order for that argument to work, he has to get you to accept the method.

The fundamental problem in this kind of reasoning is this, that faced with an anti-Christian conclusion derived using Bayes's Theorem, the non-mathematically inclined Christian historian who accepted BT on the basis of this book will reject it again after the next book, because their acceptance of the truth of Christianity is so much stronger than their acceptance of the truth of Bayes, that the only conclusion they can come to is that Bayes's Theorem must be flawed, even if in some way that is not immediately apparent. So I fear that the end result of this will be an insufferably smug Richard Carrier, who knows - beyond reasonable doubt - that he has proved that Jesus didn't exist, and a bunch of Christians who have read this, who know that Carrier must be wrong.

But Carrier does an excellent job of demonstrating that Bayes's Theorem is a valid way of estimating historical probability, and a pretty good job of demonstrating that it is the best method of estimating historical probability.

Perhaps the most interesting chapter in the book is Chapter 5, where he looks at the various criteria used by historians involved in the 'quest' for the 'Historical Jesus' and either demonstrates that each criterion reduces to Bayes's Theorem, or is invalid as a method. Thus the point is proved, Bayes's Theorem is the fundamental valid method underlying all other historicity criteria.

Taken one by one:
  1. Dissimilarity: demonstrated to be invalid.
  2. Embarrassment: similarly invalid. Carrier deconstructs this one at great length, indeed, it is the largest part of the chapter by far. Along the way, he makes a very interesting statement that I must investigate further sometime:
    "Its worth remarking here, ..., that everyone literate enough to compose books in antiquity was educated almost exclusively in the specific skill of persuasion: that is what all writing was believed to be for, and how all literate persons were taught to write." (page 134)
    Thus, everything in an ancient book was there for the purpose of convincing the reader of something, so nothing embarrassing which hindered this purpose would be included.
  3. Coherence: shown to be invalid.
  4. Multiple attestation: shown to be invalid.
  5. Explanatory credibility: consistent with Bayes, but can only exclude, never confirm.
  6. Contextual plausibility: similarly consistent with Bayes.
  7. Historical plausibility: again, consistent with Bayes, but is incomplete.
  8. Natural probability: consistent with Bayes, but doesn't make as strong a case as could be formulated with Bayes, so Bayes supersedes this method. 
  9. Oral preservability: consistent with Bayes, but can only exclude.
  10. Crucifixion (the theory has to explain why Jesus was deemed worthy of crucifixion): not valid.
  11. Fabricatory trend: consistent with Bayes, but can only exclude.
  12. Least distinctiveness: of limited use, but consistent with Bayes.
  13. Vividness of narration: shown to be invalid.
  14. Textual variance: invalid.
  15. Greek context: invalid.
  16. Aramaic context: invalid.
  17. Discourse features: invalid.
  18. Characteristic Jesus: invalid, as it relies on many of the above invalid methods.
Wow. I hadn't realised there were so many rubbish criteria in use by Historical Jesus scholars. Carrier shows that most of them are useless and the rest of them are poor-man's versions of Bayes, so to use Bayes directly is better than using any of them.

Anyway, I think I've said all I need to here. There's an interesting Jesus vs Daniel thing that I'll maybe pick up in a future post, but I'll not go into it here.

In summary, I agree with Carrier's conclusion: "Historians should be Bayesians". We'll see what happens when Bayes is applied directly to Jesus in the next book by Carrier.


Monday, July 01, 2013

Historical probability and the Son of God

I'm currently reading Richard Carrier's book "Proving History: Bayes's Theorem and the Quest for the Historical Jesus". A proper review may follow in due course, when I've finished reading the thing. Carrier is currently working on another book in which he aims to prove that Jesus never existed at all, using the methods he establishes and validates in the earlier book. But we'll have to judge that book on its own merits, when it comes out.

Here, as the title makes clear, Carrier uses Bayes's Theorem as his primary method for assessing historical hypotheses in the light of historical data. Now, I'm no stranger to Bayes's Theorem, it was the fundamental foundation of my PhD thesis (in Engineering) after all, and I'm very interested in the subject of Jesus, historical or otherwise, so I really had to read this book. 

Currently I'm about 1/3 of the way through the book, so I can't comment on where Carrier ends up, but I have a nagging doubt about the applicability of the use of Bayes's Theorem, or indeed any method of estimating historical probability here.

The problem is this. It doesn't matter which way you slice the issues, or which pieces of evidence you consider or neglect, you will never, ever reach the conclusion that Jesus was the Son of God by historical methods.

Almost by definition, Jesus, if he was the unique Son of God (whatever that means in this context), was just that, the unique Son of God. There was only one of him who ever lived. That means that historically there is only a 1 in 100 billion (approx number of people who have ever lived) chance that any given person in history was the real Son of God. Now those odds are so vanishingly small that any probabilicist would quite happily neglect that chance and simply say the chances of it are zero.

In other words, historically speaking, the chances of anyone being the Son of God are zero. Therefore, in terms of historical probability, we can say with a great degree of confidence that nobody was the Son of God, therefore, Jesus was not the Son of God. QED. Probability does work like that. But the question is whether or not reality works like that? 

My doubt is that if Jesus actually was the 1 in 1011 Son of God, then historical reasoning will never give us access to that fact. We simply cannot ever get there through historical method.

So when it comes to Carrier proving mathematically that Jesus was not the Son of God and, furthermore, did not exist at all, then that really proves nothing. The issue will be completely settled for a number of atheists who believe it anyway, but it will change nothing for even mathematically minded and rational believers (yes, they do exist), because there is always a difference between a 'vanishingly small' probability and actual zero. And it doesn't matter how small 'vanishing' is, Bayes's Theorem will always leave a tiny hole for that chink of light to shine through, for those who believe in the light.