 Lewis’s proposal is also likely to be challenged on epistemological grounds similar to those used by Kripke and Wright in dismissing the suggestion that quaddition can be ruled out in light of the fact the hypothesis that Jones meant quaddition is less simple than the hypothesis that he meant addition. A speaker can know that in response to the query ‘\(68+57\)’, ‘125’ is the answer that accords with what she meant by ‘+’, without having to infer this from facts about her previous linguistic behaviour. That is to say, in recognising that the answer ‘125’ fits what we mean by ‘+’, we do not proceed “by inference to the best semantic explanation of [our] previous uses of that expression” (Wright 2001: 109; see also Kripke 1982: 40). But this is apparently what we would have to do if the “simplicity” suggestion were correct: the best explanation would be yielded by the simplest of the hypotheses consistent with our previous linguistic behavior. The “simplicity” suggestion thus apparently makes a mystery of our (generally) non-inferential semantic knowledge. Lewis’s suggestion will be challenged on similar grounds. We do not infer what we mean by ‘+’ from facts about naturalness together with constitutive principles governing interpretation. Again, the account appears to make a mystery of the non-inferential nature of much of our semantic knowledge. Moreover, it faces difficulties in accommodating the authority normally credited to self-ascriptions of meaning. For Lewis, in virtue of the role they play in his account of scientific laws, simplicity and naturalness are objective notions. However, a speaker’s opinions about what she means, unlike, say, her opinions about the structure of the world or of our hypotheses about it, are generally authoritative, unless there are special reasons to doubt them. What might the basis for this default authority be, if what she means is determined by facts about simplicity and naturalness?