Types, Tableaus, and Gdels God [Paperback]

G?del's modal ontological argument is the centerpiece of an extensive examination of intensional logic. First, classical type theory is presented semantically, tableau rules for it are introduced, and the Prawitz/Takahashi completeness proof is given. Then modal machinery is added to produce a modified version of Montague/Gallin intensional logic. Finally, various ontological proofs for the existence of God are discussed informally, and the G?del argument is fully formalized. Parts of the book are mathematical, parts philosophical.

G?del's modal ontological argument is the centrepiece of an extensive examination of intensional logic. First, classical type theory is presented semantically, tableau rules for it are introduced, and the Prawitz/Takahashi completeness proof is given. Then modal machinery is added, semantically and through tableau rules, to produce a modified version of Montague/Gallin intensional logic. Extensionality, rigidity, equality, identity, and definite descriptions are investigated. Finally, various ontological proofs for the existence of God are discussed informally, and the G?del argument is fully formalized. Objections to the G?del argument are examined, including one due to Howard Sobel showing G?del's assumptions are so strong that the modal logic collapses. It is shown that this argument depends critically on whether properties are understood intensionally or extensionally.
Parts of the book are mathematical, parts philosophical. A reader interested in (modal) type theory can safely skip ontological issues, just as one interested in G?del's argument can omit the more mathematical portions, such as the completeness proof for tableaus. There should be something for everybody (and perhaps everything for somebody).Preface. Part I: Classical Logic. 1. Classical Logic - Syntax. 2. Classical Logic - Semantics. 3. Classical Logic - Basic Tableaus. 4. Soundness and Completeness. 5. Equality. 6. Extensionality. Part Il3Ü