Full Idea
Stalnaker's guiding idea is that in making an assertion the speaker is trying to get the audience to rule out certain possibilities. ....If all goes well, further planning will proceed on the basis of a smaller and more accurate range of possibilities.
Gist of Idea
An assertion is an attempt to rule out certain possibilities, narrowing things down for good planning
Source
report of Robert C. Stalnaker (Assertion [1978]) by Laura Schroeter - Two-Dimensional Semantics
Book Reference
'Stanford Online Encyclopaedia of Philosophy', ed/tr. Stanford University [plato.stanford.edu], p.37
A Reaction
This sounds intuitively rather plausible, and is a nice original thought. This is what we pay clever chaps like Stalnaker to come up with. It seems to imply some notion of verisimilitude (qv. under 'truth'), depending on how much narrowing happens.