That isn't Perplexed's point. Let's say that as of this moment all crows that have been observed are black, so both of his hypotheses fit the data. Why should "all crows are black" be assigned a higher prior than "All crows are black except <270 pages specifying the exceptions>"? Based on cousin_it's post, I don't see any reason to do that.

So, to revive this discussion: if we must distribute probability mass evenly because we cannot place emphasis on simplicity, shouldn't our priors be almost zero for every hypothesis? It seems to me that the "underdetermination" problem makes it very hard to use priors in a meaningful way.