Intensionality and Two-steps Interpretations

In this paper we considered the extension of the First-order Logic (FOL) by Bealer’s intensional abstraction operator. Contemporary use of the term ’intension’ derives from the traditional logical Frege-Russell’s doctrine that an idea (logic formula) has both an extension and an intension. Although there is divergence in formulation, it is accepted that the extension of an idea consists of the subjects to which the idea applies, and the intension consists of the attributes implied by the idea. From the Montague’s point of view, the meaning of an idea can be considered as particular extensions in different possible worlds. In the case of the pure FOL we obtain commutative homomorphic diagram that holds in each given possible world of the intensional FOL, from the free algebra of the FOL syntax, toward its intensional algebra of concepts, and, successively, to the new extensional relational algebra (different from Cylindric algebras). Then we show that it corresponds to the Tarski’s interpretation of the standard extensional FOL in this possible world.