 Dunn (2001, 2008) has pointed out that the analysis of information in logic is intricately related to the notions of intension and extension. The distinction between intension and extension is already anticipated in the   Port Royal Logic (1662) and the writings of Mill (1843), Boole (1847) and Peirce (1868) but was systematically introduced in logic by Frege (1879, 1892). In a modern sense the extension of a predicate, say “X is a bachelor”, is simply the set of bachelors in our domain. The intension is associated with the meaning of the predicate and allows us to derive from the fact that “John is a bachelor” the facts that “John is male” and “John is unmarried”. It is clear that this phenomenon has a relation with both the possible world interpretation of modal operators and the notion of information. A bachelor is by necessity also male, i.e., in every possible world in which John is a bachelor he is also male, consequently: If someone gives me the information that John is a bachelor I get the information that he is male and unmarried for free. 