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November 20, 2011


What does "ECREE" mean?

An Extraordinary Claim is one that seems, at first blush, to have a 'very low probability'. That is, an EC has a low 'prior probablility'.

An ancient might think the claim that the Earth is round is an EC. It looks flat to him. It's bumpy, but on average, flat. Furthermore, he's met travelers from very far away and none have even claimed to have been all the way around the Earth. They tell him, in fact, that it looks more or less flat everywhere they've been.

If you claim to this ancient that the Earth is round, the ancient would be quite sensible to insist on Extraordinary Evidence. He will want more for this claim than he will want for an Ordinary Claim such as that you had fruit at dinner last night. He will likely believe you had fruit on your say-so.

Extraordinary Evidence is evidence that, when taken into account, can raise the probability of a claim from 'very low' to 'likely' or 'very likely' or 'likely enough to believe'.

EE is Extraordinary because it can do that. Ordinary evidence is ordinary because it cannot.

So it is really a no-brainer: ECREE.

Want to know more? Look up Bayes' Theorem.

The real question is: How do you decide whether a claim 'seems, at first blush, to have a very low probability'?

Sometimes you can actually look up the prior probability of the claim. If you also know the probabilities of your evidences you can use Bayes' theorem to calculate the final probability of the claim.

In many situations, the probabilities can't be looked up or calculated - they have to be personally accessed. Some ancients might NOT think the claim that the Earth is round is so extraordinary. Perhaps they've noticed that a big rock looks flatter than a small rock - especially when viewed from very close by. Could it be this way with the Earth?

You might convince some ancients to change their minds about whether the Earth is round is an EC without really presenting final proof. You could talk about the travellers or talk about the big rock / small rock idea.

It doesn't matter whether the prior probability is looked up or personally accessed: Bayes' rules and ECREE.

Another thing: 'at first blush' can be hard to define. Do we every really have no evidence one way or the other? Is there ever really first blush? One possibility: Assign the prior probability of the particular claim according to your experience with similar claims.

Finally: If you claim a man (really) rose from the dead, I will certainly assign that a very low prior probability.

When you label this assignment a 'presupposition' on my part does that help you forget that it is a reasonable one? Why?


Why do extraordinary claims require extraordinary evidence?

Because Bayes' Theorem says so, that's why.


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