Sometimes it's called pragmatics. Sometimes it's under the bubble-theory of speech act theory. Sometimes people talk about the difference between performative and constantive meanings.
In short, it explains why we can say things that are seeming non sequiturs, but that work in the given situation. Like
Person 1: Let's go!In most technical terms, the first person gave a polite command, to which the second's response is an inappropriate response (because a command only allows "yes" or "no.") Speech act theory allows us to understand "scientifically" what native-English speakers intuitively know - the "no" in the second part is elided, and skipped straight to the explanation why they can't go yet.
Person 2: Sarah just went to the bathroom.
It doesn't have to be in a dialogue. For example,
I have tree jism in my eyesis a statement I've been pondering for a while. It doesn't mean I've been pleasuring the odd willow on my way to the archives, but that stupid allergies are stupid here.
All this because the Institute just put up some new signs. I've talked about having a confused moment with signs and slogans before. This time around, the sign says
Respected students and teachers! From April 21st, because of organizations using our institute,[the word for "using" could also be "enlightening" or "dedicated to," but those...don't make sense...]
security will be different, and entrance to the buildings will be strictly by pass or student card. Please, to avoid unpleasant situations, make sure you have the necessary documentation.Maybe, if I were a native Russian speaker, I could untangle what exactly it means, but the way I currently understand the sign I can't figure out if the organizations are renting or using a space that needs extra security, or if they mean to say that there is a new organization providing them with security, and this organization won't be as lax as the old one was.
What caused the whole connection to speech act theory is that I think the intention behind the whole sign was in order to provide those same "respected students and teachers" with a "reason" for this new demand. But they don't include any specific information, so the attempt just seems weird and vague and like a rule made to be a rule.
Which isn't unheard of in this country.