Full Idea
In 'either Socrates was a philosopher or someone other than Socrates was a philosopher', both propositions expressed by the disjuncts depend for their existence on the existence of Socrates, but the whole disjunction does not.
Gist of Idea
In 'S was F or some other than S was F', the disjuncts need S, but the whole disjunction doesn't
Source
Robert C. Stalnaker (Mere Possibilities [2012], 4.2)
Book Reference
Stalnaker,Robert C.: 'Mere Possibilities' [Princeton 2012], p.100
A Reaction
Nice example, just the sort of thing we pay philosophers to come up with. He is claiming that propositions can exist in possible worlds in which the individuals mentioned do not exist.