Via Jerry Coyne, I came across this exchange between Sam Harris and David Eagleman. Boring, standardized inaccuracies about the relationship between atheism, New Atheism, and certainty aside, I think that the problems with Eagleman's `Possibilianism' are deeper than Harris recognizes, insofar as such a thing is possible to say after flat-out inconsistency has been established.
The error which pervades his website and his talk is a simple one: a black/white split between commitment and non-commitment. He appears to be irretrievably mired in the old "believe X/believe not X/suspend judgment" trichotomy. Like many other three-horned creatures, this sort of thinking feels awfully... extinct. On first and other inspections, Possibilianism appears to be Bayesianism without the rigor. One simply enumerates possibilities - apparently as only emphasized for theism, though I do not see why other propositions should not be similarly attended to - and does not worry about things like analytical usefulness or Dutch-books or probabilistic consistency or positing any principled means of updating commitments. It looks like dodging and attention-getting; it smells like dodging and attention-getting; and yet here I am, about to give it a taste-test as well. I suspect this is about to get deeply unhealthy.
Perhaps Eagleman is wholly unfamiliar with analytic philosophy or the philosophy of science, despite his heavy allusions to the same. In Bayesianism, one holds `multiple ideas' in ones head, but not simply as possibilities but as articles with differing probabilities. As one of the simplest theories in probability runs, prob(X)+prob(~X)=1, a statement that generalizes to any finite partitioning of possibilities on the assumption of finite additivity, which is itself an implication of the stronger assumption of countable additivity, which itself yields an analogous result. Another popular standard, widely-assumed, is regularity, which states that all possible propositions have probability greater than 0.
So a Bayesian who accepts regularity as regards coherently formulated definitions of God is already holding the possibilities in mind. Further, the confidences allotted to the differing possibilities are reflected in one's prior whenever updating on new discoveries. One may even update on uncertain propositions using Jeffrey Conditioning. All around the world today, Bayesians are wagering on uncertainty and on propositions for which no decisive evidence exists. For all of these methods, there are various arguments, and the limits and applications of these methods are items of active research and discussion. In the absence of any evidence, equivocation is the most popular method. So, what exactly does David Eagleman have to offer?
T-shirts and confusion and "boy is this Universe is a counter-intuitive and amazing place!"
He uses terms like `likelihood' and other probabilistic language, but does not seem to understand probabilism. In this matter, he appears to be similar to (most of) the New Atheists, minus his uncomprehending overview. The New Atheists are if anything more consistent with probabilism in their language than is Eagleman.
It really is that bad. This sort of `oh look at my radical new way of thinking about knowledge (especially theistic belief)' annoys me to no end, especially when it comes in the form of a condescending lecture to us over-certain militant atheists/theists. If only we opened our minds to uncertainty and possibility! Then we'd all get along.
Whether it's the `God transcends existence' crowd or the `we need a new agnosticism crowd', the boring, ignorant element remains. Because these are all useless, they are all doomed to be fads, the passing symptoms of those who are uncomfortable with using accurate words for self-description, these being loathed due to exposure to various sorts of reaction and cheap sloganeering. "Oh I don't want to be dogmatic like those atheists," or "oh I don't want to be a fundamentalist like those theists." Those. Those. Not me. No way. They lazily search for Third Ways that already exist and in a form superior to their imaginations, or they simply wax incoherent; they pay little attention to existing criticisms, which they cannot know to be relevant because they are ignorant.
Gimme my TED talk, please! I'd love to profit from an exciting, revolutionary proposal of stuff that's been around for centuries. Hell, I'll make up my own new word for probabilism and decision theory and have my own movement. I'll call it `nicepersonopenmindednessism' or `uncertaintyisgoodpolicyism'. Goodness, I could write a book! To ensure originality, I'll fudge a few details. I'd hate to be thought a plagiarist. `Mysterianism' is already taken, alas. (I note that Mysterianism is actually worth looking at.)
Edit (9/5/2011): I would recommend reading this before watching the TED talk.