The Dawn Treader

It turns out that Bayes is used quite actively in Christian apologetics.

For starters, Dr. Alvin Plantinga uses a Bayesian argument in his famous Evolutionary Argument Against Naturalism.  Plantinga examines the probability of human cognitive faculties' being reliable, given that human cog faculties have been produced by evolution.  By now, you recognize that this is a conditional probability (hint: the word "given" gives it away).  When you see conditional probabilities, start thinking Bayesian.

Dr. JP Moreland offers a modest use of Bayes Theorem in his argument for design offered in The Creation Hypothesis.  A nice blog post describing this argument is found here.  Moreland uses one of the variant forms of Bayes to calculate a positive posterior probability that a theistic designer exists.  Moreland's argument here is modest, in my opinion -- but it is still a nice demonstration of Bayesian reasoning in apologetics.

Then we have Dr. Robin Collins of Messiah college.  He applies Bayesian thinking in comparing two competing hypotheses: the atheist single-universe hypothesis versus the theistic universe hypothesis.  Collins says,

"The prime principle of confirmation is a general principle of reasoning which tells us when some observation counts as evidence in favor of one hypothesis over another. Simply put, the principle says that whenever we are considering two competing hypotheses, an observation counts as evidence in favor of the hypothesis under which the observation has the highest probability (or is the least improbable). (Or, put slightly differently, the principle says that whenever we are considering two competing hypotheses, H1 and H2, an observation, O, counts as evidence in favor of H1 over H2 if O is more probable under H1 than it is under H2.) Moreover, the degree to which the evidence counts in favor of one hypothesis over another is proportional to the degree to which the observation is more probable under the one hypothesis than the other."

What Collins is talking about are conditional probabilities given evidence : once again, Bayes is used to show how evidence favors one hypothesis versus another, and to what degree it supports one hypothesis over another.  Good stuff.

Finally, we have the famous Bart's Blunder comment in the .  Craig shows that Ehrman fails to fully apply Bayes Thereom in order to try to determine the probability of the resurrection given the evidence for the resurrection.  Ehrman simply ignores Bayes Theorem and asserts that the likelihood (i.e. conditional probability) of the resurrection is nil because miracles are by definition improbable -- which is mathematically fallacious.  Craig calls him on it.

It may interest you to know, however, that not all Christian apologists are so quick to use Bayesian arguments.  In fact, one prominent one, Dr. Bill Dembski, warns against it in Chapter 33 of The Design Revolution.

I'll explain why in a future post.