<p>In this thesis we use the syntactic-semantic method of constructive type theory to give meaning to classical logic, in particular Gentzen's LK.</p><p>We interpret a derivation of a classical sequent as a derivation of a contradiction from the assumptions that the antecedent formulas are true and that the succedent formulas are false, where the concepts of truth and falsity are taken to conform to the corresponding constructive concepts, using function types to encode falsity. This representation brings LK to a manageable form that allows us to split the succedent rules into parts. In this way, every succedent rule gives rise to a natural deduction style introduction rule. These introduction rules, taken together with the antecedent rules adapted to natural deduction, yield a natural deduction calculus whose subsequent interpretation in constructive type theory gives meaning to classical logic.</p><p>The Gentzen-Prawitz inversion principle holds for the introduction and elimination rules of the natural deduction calculus and allows for a corresponding notion of convertibility. We take the introduction rules to determine the meanings of the logical constants of classical logic and use the induced type-theoretic elimination rules to interpret the elimination rules of the natural deduction calculus. This produces an interpretation injective with respect to convertibility, contrary to an analogous translation into intuitionistic predicate logic.</p><p>From the interpretation in constructive type theory and the interpretation of cut by explicit substitution, we derive a full precision contraction relation for a natural deduction version of LK. We use a term notation to formalize the contraction relation and the corresponding cut-elimination procedure.</p><p>The interpretation can be read as a Brouwer-Heyting-Kolmogorov (BHK) semantics that justifies classical logic. The BHK semantics utilizes a notion of classical proof and a corresponding notion of classical truth akin to Kolmogorov's notion of pseudotruth. We also consider a second BHK semantics, more closely connected with Kolmogorov's double-negation translation.</p><p>The first interpretation reinterprets the consequence relation while keeping the constructive interpretation of truth, whereas the second interpretation reinterprets the notion of truth while keeping the constructive interpretation of the consequence relation. The first and second interpretations act on derivations in much the same way as Plotkin's call-by-value and call-by-name continuation-passing-style translations, respectively.</p><p>We conclude that classical logic can be given a constructive semantics by laying down introduction rules for the classical logical constants. This semantics constitutes a proof interpretation of classical logic.</p>

In this thesis we use the syntactic-semantic method of constructive type theory to give meaning to classical logic, in particular Gentzen's LK. We interpret a derivation of a classical sequent as a derivation of a contradiction from the assumptions that the antecedent formulas are true and that the succedent formulas are false, where the concepts of truth and falsity are taken to conform to the corresponding constructive concepts, using function types to encode falsity. This representation brings LK to a manageable form that allows us to split the succedent rules into parts. In this way, every succedent rule gives rise to a natural deduction style introduction rule. These introduction rules, taken together with the antecedent rules adapted to natural deduction, yield a natural deduction calculus whose subsequent interpretation in constructive type theory gives meaning to classical logic. The Gentzen-Prawitz inversion principle holds for the introduction and elimination rules of the natural deduction calculus and allows for a corresponding notion of convertibility. We take the introduction rules to determine the meanings of the logical constants of classical logic and use the induced type-theoretic elimination rules to interpret the elimination rules of the natural deduction calculus. This produces an interpretation injective with respect to convertibility, contrary to an analogous translation into intuitionistic predicate logic. From the interpretation in constructive type theory and the interpretation of cut by explicit substitution, we derive a full precision contraction relation for a natural deduction version of LK. We use a term notation to formalize the contraction relation and the corresponding cut-elimination procedure. The interpretation can be read as a Brouwer-Heyting-Kolmogorov (BHK) semantics that justifies classical logic. The BHK semantics utilizes a notion of classical proof and a corresponding notion of classical truth akin to Kolmogorov's notion of pseudotruth. We also consider a second BHK semantics, more closely connected with Kolmogorov's double-negation translation. The first interpretation reinterprets the consequence relation while keeping the constructive interpretation of truth, whereas the second interpretation reinterprets the notion of truth while keeping the constructive interpretation of the consequence relation. The first and second interpretations act on derivations in much the same way as Plotkin's call-by-value and call-by-name continuation-passing-style translations, respectively. We conclude that classical logic can be given a constructive semantics by laying down introduction rules for the classical logical constants. This semantics constitutes a proof interpretation of classical logic.

Dans cette thèse nous étudions les sémantiques ludothéoriques, conçues comme les altérnatives à la sémantique traditionelle de Tarski, qui metent en marche le princip Meaning is in use et l’idée des jeux de language de second Wittgenstein: le sens des constantes logiques est donné par les règles qui en fixent l’usage et qui apparaissent dans les interactions social que sont les jeux de langage. Deux traditions ludotheorique sont présentées: Game Theoretical Semantics (GTS), proposé par Hintikka et Sandu en 1968 et Dialogical logic, proposé initialement par Paul Lorenzen et Kuno Lorenz en 1955 et developé à partir de 1993 par Shahid Rahman et ses collègues. En 1989 Hintikka et Sandu ont arrivé à l’idée des jeux avec des informations imparfaits qui les a emmené à Independence Friendly Logique (IF logic), logique du premiere ordre qui dépasse en expressivité la logique classique. Deux chapitres de cette thèse sont consacrés à l’axiom de choix et au traitement de l’anaphore, deux sujets choisis par Hintikka pour démontrer la fécondité de la logique IF et de GTS. Le but de cette thèse et de montrer que’il est possible de rendre compte aussi bien et à moindre frais dans le cadre dialogique. Plus précisément, la logique IF est comparée avec la théorie constructive des types dans la forme dialogique pour conclure à la supériorité de cette dernière qui a le même pouvoir explicatif qu’IF sans sacrifier pour autant la dimension inférentielle de la logique. / This thesis studies game-theoretically oriented semantics which provide an alternative to traditional Tarski-style semantics, implementing Wittgenstein’s idea of the meaning as use. Two different game theoretical traditions are presented: Game Theoretical Semantics (GTS), developed by Jaako Hintikka and Gabriel Sandu, and Dialogical logic, first introduced by Paul Lorenzen and Kuno Lorenz and further developed by Shahid Rahman and his associates. In 1989 Hintikka and Sandu came up with games with imperfect information. Those games yielded Independence friendly first-order logic (IF logic), exceeding the expressive power of classical first-order logic. It is expressive enough to enable formulating linearly, and at the first-order level, sentences containing branching quantification. Because of this characteristic, Hintikka claims that IF logic is most suitable for at least two main purposes: to be the logic of the first-order fragment of natural language; and to be the medium for the foundation of mathematics. This thesis aims to explore the above uses of IF logic. The properties of IF logic are discussed, as well as the advantages of this approach such as the possibility of taking account of (in)dependency relations among variables; GTS-account of two different notions of scope of quantifiers; the “outside–in” direction in approaching the meaning, which turns out to be advantageous over the traditional “inside-out” approach; the usefulness of game-theoretic reasoning in mathematics; the expressiveness of IF language, which allows formulating branching quantifiers on the first-order level, as well as defining the truth predicate in the language itself. We defend Hintikka’s stance on the first-order character of IF logic against some criticisms of this point. The weak points are also discussed: first and foremost, the lack of a full axiomatization for IF logic and second, the problem of signalling, a problematic phenomenon related to the possibility of imperfect information in a game. We turn to another game-theoretically oriented semantics, that of Dialogical Logic linked with Constructive Type Theory, in which dependency relations can be accounted for, but without using more means than constructive logic and the dialogical approach to meaning have to offer. This framework is used first to analyse and confront Hintikka’s take on the axiom of choice, and second to analyse the GTS account of anaphora.