The Probability of the Possible

___________________________________________ In “Why is There Anything at All?” Peter van Inwagen argues that even though it was never necessary that concrete beings existed, it was always maximally probable – just short of necessity – that they did (van Inwagen, 1996). I argue that van Inwagen’s argument fails, albeit for an interesting reason which has remained so far unnoticed in the literature: there is a critical tension between two of its premises, both essential to its soundness, concerning the nature of comprehensively specified possible worlds. I summarize van Inwagen’s argument, develop this objection, and then describe more problems which invariably accrue when we try to ascribe probability values to possible worlds.