 First, to adapt R. M. Hare’s canonical example (1952, §5.2), if I mentioned to you that one possible act was right, and another wrong, despite these acts being exactly alike in all other respects, your initial reaction would be puzzlement, and if I persisted in my view upon interrogation, you might start to worry that I was simply confused or misusing words. Second, the crucial cases used to support supervenience—like the embezzling banker case—seem to involve conceivability reasoning: we are asked to consider two circumstances that are identical in all base respects, and notice that we cannot make sense of the idea that they differ in ethical respects. Some philosophers find it natural to think that conceivability reasoning first and foremost reveals facts about conceptual possibility and necessity. This can be bolstered by a third (much more controversial) thought. Conceivability reasoning appears to be a priori. But if such reasoning fundamentally concerned the world rather than our concepts, then we would seemingly have a priori access to substantive facts about the world, which many philosophers have found deeply mysterious.