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its subject even has a referent at all. (Thus did Frege attack the Problem of
Apparent Reference to Nonexistents.)
As sketched so far, Frege's view sounds like a version of the Proposition
Theory. And so it is; it is prey to the various objections raised against that
theory in chapter 5. But Rudolf Carnap (1947/1956), Richard Montague
(1960, 1970), and Jaakko Hintikka (1961) developed intensional logic, giving
a possible-worlds interpretation and explication of Fregean senses. Here,
roughly, is the idea.
A singular term or a predicate is said to have both an extension (in the
sense introduced in the previous chapter) and a Fregean sense or "intension."
The trick is to construe a term's intension as a function from possible worlds
to extensions. Thus, the intension of a predicate is a function from worlds to
sets of things existing in those worlds that are in the predicate's extensions in
those worlds
annaabi.ee 
