Parmenides insisted that we could not even think of non-being (though apparently we could say that)! At least since then there have been (and still are ) two traditions, one maintaining that about nothing we could speak positively, saying for example that it has features, or, significantly for the Abrahamic religions, that 'from it' everything was created, and the other that all true sentences in which 'nothing' figures as subject or topic have the logical form of negative sentences denying claims about what there is or could be. This paper traces part of the history of the debate focusing first on Fridugisus of Tours and Anselm of Canterbury as representatives of the two traditions and taking up a later medieval debate involving Walter Burley and William Ockham about the coherence of reference to impossibilia. At stake are issues about criteria of ontological commitment, the relation between being and thinkability and (even) the distinction between nothing and God!
