ABSTRACT
According to Grice's theory of "conversational implicature," such implications are generated by a set of principles that govern cooperative conversation. First, very often a speaker uses a sentence to convey something other than what that sentence literally means, for example in sarcasm or in broad hinting. Second sort of nonlogical implication is suggested by P. F. Strawson's criticism of Bertrand Russell's Theory of Descriptions: a notion of "presupposition" distinct from entailment in that, when a sentence's presupposition fails, the sentence is not false but lacks truth-value entirely. Third, some implications are carried by the choice of a special word, such as "but" as opposed to "and," in that "but" means just the same as "and" except for carrying a contrastive connotation. Grice calls this phenomenon "conventional implicature." Fourth, there are some sentences that would standardly be used to perform speech acts other than the acts indicated by their grammatical moods and semantic contents.
