Full Idea
A proposition gives reality a degree of freedom; it draws a line round the facts which agree with it, and distinguishes them from those which do not.
Gist of Idea
A proposition draws a line around the facts which agree with it
Source
Ludwig Wittgenstein (Lectures 1930-32 (student notes) [1931], B XIII.2)
Book Reference
Wittgenstein,Ludwig: 'Lectures in Cambridge 1930-32', ed/tr. Lee,Desmond [Blackwell 1980], p.56
A Reaction
This seems to be the idea of meaning as the range of truth conditions. Propositions as sets of possible worlds extends this into possible facts which agree with the proposition. Most facts neither agree nor disagree with some proposition.