A Defense of the Principle of Indifference

Abstract

The principle of indifference (hereafter ‘Poi’) says that if one has no more reason to believe A than B (and vice versa), then one ought not to believe A more than B (nor vice versa). Many think it’s demonstrably false despite its intuitive plausibility, because of a particular style of thought experiment that generates counterexamples. Roger White (2008) defends Poi by arguing that its antecedent is false in these thought experiments. Like White I believe Poi, but I find his defense unsatisfactory for two reasons: it appeals to false premises, and it saves Poi only at the expense of something that Poi’s believers likely find just as important. So in this essay I defend Poi by arguing that its antecedent does hold in the relevant thought experiments, and that the further propositions needed to reject Poi are false. I play only defense in this essay; I don’t argue that Poi is true (even though I think it is), but rather that one popular refutation is faulty. In showing this, I also note something that has to my knowledge gone unnoticed: given some innocuous-looking assumptions the denial of Poi is equivalent to a version of epistemic permissivism, and Poi itself is equivalent to a version of epistemic uniqueness.