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.

5 comments:

David Evans said...

That's a crummy argument. Let's apply it to another case.

Only one man can be the first to step onto the moon. 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 that man. 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 that man are zero. Therefore, in terms of historical probability, we can say with a great degree of confidence that nobody was the first man on the Moon, therefore, Neil Armstrong was not the first man on the Moon.

Convinced?

Nevertheless, historical arguments can decide whether Neil Armstrong was the first man on the Moon

Ricky Carvel said...

This is one of these 'extraordinary claims need extraordinary evidence' situations. It is vanishingly unlikely that a guy called Neil could have walked on the moon, but in this instance there is an extraordinary amount of evidence which is sufficient to overcome the tiny odds. But put 2000 years of history in between the supposed event and us and there is now no way we can ever have enough evidence to conclude that Jesus was the Son of God, even if he was.

David Evans said...

"But put 2000 years of history in between the supposed event and us and there is now no way we can ever have enough evidence to conclude that Jesus was the Son of God, even if he was."

I tend to agree with that. But not because of the "1 in 100 billion" figure. The 100 billion are irrelevant to how much evidence we have or could have about Jesus.

Vain Saints said...

"But put 2000 years of history in between the supposed event and us and there is now no way we can ever have enough evidence to conclude that Jesus was the Son of God, even if he was."

So I guess in 2,000 years, there will be no good reason to believe that Neil Armstrong was the first man on the moon?

Bad reasoning has a tendency to propound itself. I anticipate an argument from superior documentation in 1969 than 33AD. However, in 4,000 AD it's reasonable to conclude that techniques of forgery will have advanced as rapidly, to the point where anything could be claimed to have been a forgery.

We have evidence for Christ's Deity. A lot of people like to think it's realistic and critically minded to pretend that the evidence we have does not exist. It is not airtight; there is room for doubt, but it isn't nothing, and the talk of 2K years is just astonishingly irrelevant.

Ricky Carvel said...

Well, they way I'd put it is that in 2000 years time, we won't have sufficiently good evidence to base "the most important decision of your life" on whether or not Neil Armstrong walked on the moon.

Believing something about history is one thing. Basing your entire belief structure and major life decisions on that belief is an entirely different thing.

And, of course, there are plenty of people today who believe that nobody has walked on the moon...