In a discussion of rule-following inspired by Wittgenstein, Kripke asks us to consider the relation which holds between meaning plus by ‘+’ and answering questions like, ‘What is the sum of 68 and 57?’. A dispositional theory has it that if you mean plus by ‘+’ then you will probably answer, ‘125’. That is because, according to such a theory, to mean plus by ‘+’ is, roughly speaking, to be disposed, by and large, and among other things, to answer such questions with the correct sum. Kripke wants to emphasize, by contrast, that if you mean plus by ‘+’ then, faced with the question, ‘What is 68 + 57?’ you ought to answer, ‘125’. One could sum up the assumption about meaning which appears to underpin this criticism of dispositional theories in terms of the slogan that meaning is normative. Allan Gibbard gives us a way of reading that slogan which is suggested by Kripke's brief remarks:
The crux of the slogan that meaning is normative … might be another slogan: that means implies ought. To use roughly Kripke's example, from statements saying what I mean by the plus sign and other arithmetic terms and constructions, it will follow that I ought to answer ‘7’ when asked ‘What's 5 + 2?’.