Expert witnesses in semantics are controversial, since juries are the ultimate authorities on meaning. However, this article presents evidence that a semantics expert witness may be able to facilitate the accurate interpretation of linguistic evidence by helping jurors tap their own natural, intuitive judgements about what sentences in evidence would actually have meant in the context in which they were produced. Through controlled studies, I show that almost all speakers choose interpretations predicted by Grice’s conversational maxims if they are allowed to hear evidence from conversations in real conversations. In contrast, most speakers endorse a different interpretation, one predicted by logical semantic rules that coincide with their ideas of how language ought to work, when the same linguistic evidence is presented for careful examination. Instruction in linguistics reduces this difference significantly, but does not erase it. For jurors to interpret linguistic material from conversations accurately, then, they need both the relevant linguistic principles and the results of empirical studies of subjects who heard the material from the case at hand in the conversational medium in which it occurred.