Doubt that a supernatural being exists is banal, but the more radical doubt that we exist, at least as anything more than nominal, marginally integrated entities having convenient labels like "Myrtle" and "Oscar," is my candidate for Dangerous Idea. This is, of course, Hume's idea — and Buddha's as well — that the self is an ever-changing collection of beliefs, perceptions, and attitudes, that it is not an essential and persistent entity, but rather a conceptual chimera. If this belief ever became widely and viscerally felt throughout a society — whether because of advances in neurobiology, cognitive science, philosophical insights, or whatever — its effects on that society would be incalculable. (Or so this assemblage of beliefs, perceptions, and attitudes sometimes thinks.)