  This general worry arises in a particularly acute way for Lewis’s theory. Consider some sentence \(S\) that we would never normally use, perhaps because it is too long or too grammatically complex. Suppose that some speaker nevertheless utters \(S\). As Lewis acknowledges, we would not normally believe that the speaker was thereby attempting to speak truthfully. Instead, we would suspect that the speaker was acting for some deviant reason, such as trying to annoy, or settling a bet, and so on. We would not normally trust the speaker. But then Lewis cannot use his convention of truthfulness and trust to underwrite a unique truth-condition for \(S\).