Full Idea
Carnap's proposal is to understand the category of intensions appropriate to sentences (his 'propositions') as sets of possible worlds. The intension of the sentence is taken as the set of all possible worlds in which the sentence is true.
Gist of Idea
The intension of a sentence is the set of all possible worlds in which it is true
Source
report of Rudolph Carnap (Meaning and Necessity [1947]) by David Kaplan - Transworld Heir Lines p.90
Book Reference
'The Possible and the Actual', ed/tr. Loux,Michael J. [Cornell 1979], p.90
A Reaction
[reference?] This extension of the truth-conditions view of meaning strikes me as being very attractive. Except that whole worlds hardly seem to be relevant to my remark about how lunch might have been improved.