Bennett, Jonathan - Locke, Berkeley Hume: Central Themes

Someone may utter words and mean nothing by them, or hear words and understand nothing by them: communication involves not just uttering and hearing, but also meaning and understanding. What is it to attach a meaning to an utterance? Or, to take plainly related questions, what is it for a type of utterance to have a meaning, or for a system of such types to constitute a language? I intend these as questions about the meaning of 'mean', 'language' and so on, not about what else goes on when someone speaks with meaning, hears with understanding or the like.