Full Idea
We generally take an assertion's domain of discourse to be implicitly restricted by context. [Note: the standard approach is that this restriction is a semantic phenomenon, but Kent Bach (2000) argues that it is a pragmatic phenomenon]
Gist of Idea
The domain of an assertion is restricted by context, either semantically or pragmatically
Source
Rayo,A/Uzquiasno,G (Introduction to 'Absolute Generality' [2006], 1.1)
Book Reference
'Absolute Generality', ed/tr. Rayo,A/Uzquiano,G [OUP 2006], p.1
A Reaction
I think Kent Bach is very very right about this. Follow any conversation, and ask what the domain is at any moment. The reference of a word like 'they' can drift across things, with no semantics to guide us, but only clues from context and common sense.