Anselm built his meditation Proslogion on the formula ‘that than which nothing greater can be conceived’. The peculiarity of this phrase has been often remarked but not, I believe, fully appreciated. Properly understood, I shall argue, this formula, although unable to support the so-called ontological argument, throws important light on the logic of the religious use of the word ‘God’. My argument will turn on the difference between the two uses of the verb ‘conceive’ in Anselm's claim that we can conceive of that than which nothing greater can be conceived.