Anselm’s original argument for the existence of God seems to pull in opposite directions. On the one hand, it is not easy to see what, if anything, is wrong with it; on the other, it seems incredible that the existence of a being like God could be proved entirely a priori. This paper presents a diagnosis of what seems to be wrong with Anselm’s original reasoning. The diagnosis is general enough to be of use elsewhere, and it is this: conceptual (...) possibilities are inferential dead-ends, not free inference tickets to prove any substantial claim. It remains to be seen if other versions of Anselm’s original insight, both contemporary and not, fall into the same conceptual possibility trap. (shrink)