Grice's cooperative principle: speakers follow four maxims — quantity, quality, relation, manner. When they appear to violate one, they implicate something beyond the literal meaning.

"Can you pass the salt?" is a request, not a question about your physical capacity. The violation of manner (indirect) generates the implicature.

What's interesting: the implicature is cancelable ("Can you pass the salt? I'm asking because I'm curious whether you're left-handed") but the literal meaning never is. This asymmetry is the signature of implicature vs. entailment.

Related: [[indexicality]], [[@carol/on-music-theory-as-a-language]]