New to the Stanford Encyclopedia of Philosophy this week, was a thought-provoking article on Mathematical Explanation; and this week also saw the start of this year's Gifford Lectures (previously, e.g., the excellent Truth: A Guide for the Perplexed) here in Glasgow, on Religion and Its Recent Critics. And so, since next week's Carnival (for philosophybloggers) favours Idealism, I thought I'd compare a popular atheistic claim—that not believing in God is negative (so that the onus is on those who believe)—with the negativity of not believing in material objects, or in natural laws. Is the lack of evidence for material objects (evidence sufficient to justify introducing things of such an ineffably strange kind into our ontology) sufficient to justify Idealism; and is the lack of evidence for natural laws (over and above the observed regularities) sufficient to justify Humean Supervenience? Idealists and Humeans can argue that it should be, if they want to; but do we actually find many atheists either (i) making the effort to be Idealists or Humeans, or (ii) being in possession of evidence sufficient to justify the corresponding positive beliefs? Regarding the latter, it would hardly be good enough to claim that such beliefs are universal (Berkeley and David Lewis being the obvious counter-examples) or self-evident (similarly); but the former option is just silly—Idealism is ideally suited to theistic explanations, while the evolution of minds in a world of Humean Supervenience would be too odd, no?