 The example Kripke chooses to illustrate the problem is that of addition. What is it to grasp the rule of addition? The application of the rule is potentially infinite, and bizarre interpretations of the rule, as well as the standard use of it, are compatible with any finite set of applications of the usual sort such as 7 + 14 = 21. So what is it which makes it true that when I say ‘plus’ I mean the usual addition function and not some other? Kripke (pp. 62–71) understands this question as containing a Humean problem to which, he claims, Wittgenstein gives a Humean, ‘sceptical’ solution.