Any serious math problem causes my eyes to glaze over, my mind to wander, and produces a thin trickle of saliva to dribble from my lips. I’m truly stupefied by difficult equations.
I admitted this to Dr. Richard Carrier when I interviewed him for my recent podcast. My previous post discussed this conversation, and introduced his book and his project. Let’s quickly review: Carrier’s recent book, Proving History: Bayes’s Theorem and the Quest for the Historical Jesus, critiques the method and criteria historians use to do their work. He focuses primarily on the practice as applied to the historical Jesus, but his criticism is also directed at historical practices in general.
Carrier applies Bayes’ Theorem to the historical method. Bayes’ Theorem is a mathematical calculation formulated by the mathematician Thomas Bayes in the mid-18th century. While it has been used in probability theory, it has been recognized that the equation describes a logical argument. This is why Carrier is applying it to the practice of history, and more specifically, the historicity of Jesus. This is how Carrier described Bayes’ Theorem,
It’s a theorem about how we reason about probabilities, or how to correctly reason about probabilities, and it just so happens that all empirical reasoning is all probabilistic. Everything that we claim to know about facts comes down to probabilities, not certainties. … Once you start realizing that all empirical statements are probabilistic like that, then correct empirical reasoning has to be described by whatever theory correctly describes probabilistic reasoning, and that’s Bayes’ Theorem.
This is all well and good. But if you’re like me, you fear math like you fear apocalyptic zombies. But you needn’t worry, our podcast was non-technical, as is this post, and Carrier’s book is easy to read. (Zombies aren’t real, either. No, really.) During our talk Carrier fielded the common complaint that he is simply reducing history to math:
First of all, we’re already doing the math in our heads, whether we’re aware of it or not or whether we’re thinking in terms of math. We’re weighing probabilities, we’re already doing it. So the question is, are we going to do it soundly or not?
The basic Baysean equation looks daunting, and you have to invest a little bit of brain fuel to get the basic idea. However, it’s truly not as difficult as it appears. You can read about and study the theorem here and here.
In chapter 4 of his book, Carrier examines historical methods through the lens of this theorem. He looks at the Argument to the Best Explanation and the Argument from Evidence, in particular. Carrier states that all hypothetico-deductive methods reduce to Baysean reasoning.
Bayes’ Theorem describes them all. I think this is a very important discovery, and it’s a very important thing to understand, especially because a lot of historians are very fond of those other methods. But there are serious flaws in them if you don’t understand why they’re valid, or in what conditions they are valid. And Bayes’ Theorem answers those questions, so they really do need to understand Bayes’ Theorem to understand why those methods work.
In chapter 5, Carrier focuses on a Baysean analysis of historical criteria in the field of Jesus studies. He studies specific arguments scholars use, such as the Argument from Dissimilarity, The Argument from Embarrassment and what’s called Multiple Attestation. Carrier mentions 18 criteria, but there are many more.
The Argument from Embarrassment, for instance, states that if an author writes something that would embarrass him, it must be true, because he wouldn’t humiliate himself with a falsehood. Thus, any source embarrassing to Christianity is more likely true, since early Christians wouldn’t have created material that portrays the religion negatively.
Carrier illustrates common problems with these criteria: They are either applied incorrectly, or they are logically invalid, or they don’t solve the threshold problem. The threshold problem asks this question: When do we have enough evidence to warrant belief in a conclusion? When is enough enough? Carrier examines the logical foundations for all these criteria.
Carrier plans to publish part two of this book, On the Historicity of Jesus Christ, next year. It utilizes the method Carrier currently argues for. Until then, I’m keeping a calculator, a caffeinated beverage, and a crossbow nearby. I fear the mathematician zombie the most.