Full Idea
Lewis must seek some ontological ground for the grouping of possibilia into disjoint worlds.
Gist of Idea
What are the ontological grounds for grouping possibilia into worlds?
Source
comment on David Lewis (Possible Worlds [1973]) by William Lycan - The Trouble with Possible Worlds 07
Book Reference
'The Possible and the Actual', ed/tr. Loux,Michael J. [Cornell 1979], p.297
A Reaction
I do love people like Lycan who ask the simple commonsense questions about these highly sophisticated systems that students of philosophy are required to study. If a proposition is a 'set of worlds', understanding a proposition is beyond me.