Grice's Maxims
Paul Grice was a philosopher of language whose Maxims of Conversation I find myself wanting to reference fairly often. It's not that I think they're correct in a deep sense (more on that later), but I do think they're extremely useful touchpoints, and I wish everyone knew them so I could quickly reference them.
The idea is that most people will usually obey these four norms in conversation, and will generally expect (subconsciously) that you are following the norms too. They are (paraphrased):
- People will try to be relevant to the thing said before (the maxim of relation).
- People will to speak as clearly, as briefly, and as orderly as possible (the maxim of manner).
- People will try to give as much information as needed, but not more (the maxim of quantity).
- People will try to say true things, and not to say false or unsupported things (the maxim of quality).
Again, I don't think these are good as Rules You Must Follow In Every Conversation, or that they universally describe what people actually do.
But I do think they're a reasonable description of what many people are doing in many kinds of conversations, and a reasonable baseline for what you can assume many other people will assume you're doing when you're conversing, such that it's useful to know them and useful to signal when you're planning to deviate from them. Like conventions of a literary genre, it's fine to rebel against the expectations, but that's very different from just not-knowing them.
So, for example: in general, people will assume that the next thing you say in a conversation will be directly related to the last thing spoken by the last person who spoke. Different people have different thresholds of relevance, which is already a good thing to be aware of. But if you have a very low relevance threshold, and you're launching into a story that's only tangentially relevant to what came before, you should be aware that the whole time you're saying it the listeners are liable to be trying to figure out why you're telling this story and how it connects to what was said previously, creating large cognitive overhead for them.
It's a little like when GoogleMaps keeps re-routing as you drive in the opposite direction that it thought you were going in, constantly spending its brainpower on figuring out how you could possibly get from where you are to where you said you're going, when actually you just weren't going where it thought any more. So it's polite – if you're going to say something not-super-relevant – to flag that explicitly, so people aren't left trying to connect the dots that aren't actually there.