 We most commonly explain why people do A with the intention of doing B by explaining why they believe they will do B by doing A, or why they want to do B. We can explain why speakers intend to convey a thought by uttering a sentence that says something else in the same ways. Why do speakers believe they can convey thoughts by means of the various figures and modes of speech identified in  §4?  One reason is that they have seen others doing so. Knowledge of the common forms of implicature is acquired along with knowledge of the semantics and syntax of our native language. Speakers pick up figures and modes of speech from other speakers, as they learn vocabulary and grammar. After speakers have become proficient, their own past success in using figures and modes of speech is a reason for them to believe they will succeed again. Knowledge of both figures and modes is as tacit as our knowledge of syntax and semantics. It is not knowledge of facts that define a language, but of how a language is used and understood. Since the figures and modes do not depend on a particular language, they can be used with any language.