Suppose I say to you “I went into a bar and I got drunk”. You reply: “How many drinks did you have in the bar?” I say “None—I was drunk before I went in there”. You retort: “Then why did you say you got drunk in the bar?” I say “I never said that; I merely said that I went into a bar and I got drunk—I never said I got drunk in the bar”. This illustrates the distinction between what is strictly said in an utterance—what proposition is literally expressed by the words uttered—and what is conversationally implied by the utterance. Grice used this distinction to argue that “and” is always semantically a truth-functional connective, with the temporal element assigned to pragmatic factors. He argued that we can see this from the fact that the implication of temporal succession in the events reported can be canceled without contradiction, as by saying “I went into a bar and I got drunk, but I bought coffee at the bar having got drunk at a wedding previously”. A careful report of what I strictly said would limit itself to semantic content, but an audience might naturally assume that I meant I got drunk in the bar; maybe I did, but Grice’s point is that I never actually said that.
Irony depends on this Gricean distinction—meaning the opposite of what you say. This is why reporting an ironic speech act can be tricky. Philosophers who know their Grice are constantly aware of this distinction and often exploit it to make clever remarks to other philosophers—gleefully canceling the “implicature” without contradiction. This is how we amuse ourselves on a Saturday night. Outsiders don’t get it, unless they have been schooled in Gricean philosophy of language. This can cause misunderstandings. Maybe Grice should be taught in high school, along with Darwin.