Full Idea
A pragmatic constraint might say that as different possibilities are live in different conversational settings, a different proposition may be expressed by 'If A,B' in different conversational settings.
Gist of Idea
Does 'If A,B' say something different in each context, because of the possibiites there?
Source
Dorothy Edgington (Conditionals (Stanf) [2006], 4.1)
Book Reference
'Stanford Online Encyclopaedia of Philosophy', ed/tr. Stanford University [plato.stanford.edu], p.19
A Reaction
Edgington says that it is only the truth of the proposition, not its content, which changes with context. I'm not so sure. 'If Hitler finds out, we are in trouble' says different things in 1914 and 1944.