Gabriel Sandu

The paper argues that there are two main kinds of joint action, direct joint bringing about (or performing) something (expressed in terms of a DO-operator) and jointly seeing to it that something is the case (expressed in terms of a Stit-operator). The former kind of joint action contains conjunctive, disjunctive and sequential action and its central subkinds. While joint seeing to it that something is the case is argued to be necessarily intentional, direct joint performance can also be nonintentional. Actions performed by social groups are analyzed in terms of the notions of joint action (basically DO and Stit).A precise semantical analysis of the aforementioned kinds of joint action is given in terms of time-trees. With each participant a tree is connected, and the trees are joined defining joint possible worlds in terms of state-expressing nodes from the trees. Sentences containing DO and Stit are semantically evaluated with respect to such joint possible worlds. Intentional joint actions are characterized in terms of the notion of we-intention (joint intention), characterized formally by means of a special operator.

entities in mathematics There is a line of argument which keeps ontological commitments to the minimum by making use of conservativity results. The argument goes back to Hilbert who set its general frame. Hilbert’s concern was with certain abstract (ideal) entities in mathematics but the argument has been applied without discrimination to avoid ontological commitment to mathematical entities in physics (Field) or to avoid an ontological commitment to substantial properties in the case of truth (Horwich, Field, Williams).

Deflationists have argued that truth is an ontologically thin property which has only an expressive function to perform, that is, it makes possible to express semantic generalizations like 'All the theorems are true', 'Everything Peter said is true', etc. Some of the deflationists have also argued that although truth is ontologically thin, it suffices in conjunctions with other facts not involving truth to explain all the facts about truth. The purpose of this paper is to show that in the case of arithmetic, it is difficult to combine the expressive with the explanatory function of truth if the latter is understood in a deflationist way. We will make our point by investigating several logical systems: first-order logic, full second-order logic, and existential second-order (?11-) logic.

We study partiality in propositional logics containing formulas with either undefined or over-defined truth-values. Undefined values are created by adding a four-place connective W termed transjunction to complete models which, together with the usual Boolean connectives is shown to be functionally complete for all partial functions. Transjunction is seen to be motivated from a game-theoretic perspective, emerging from a two-stage extensive form semantic game of imperfect information between two players. This game-theoretic approach yields an interpretation where partiality is generated as a property of non-determinacy of games. Over-defined values are produced by adding a weak, contradictory negation or, alternatively, by relaxing the assumption that games are strictly competitive. In general, particular forms of extensive imperfect information games give rise to a generalised propositional logic where various forms of informational dependencies and independencies of connectives can be studied

Linguistique et philosophie logique du langage: deux traditions de pensee que bien des choses opposent. La premiere est plutot mentaliste, et orientee vers l'etude de la syntaxe; la seconde, plus preoccupee de semantique, cherche volontiers le sens dans les conditions de verite des phrases. Ce portrait n'est pas faux, mais il est incomplet: entre logique et linguistique, les relations n'ont pas ete, ne sont pas que d'opposition. Dans cet ouvrage, les auteurs proposent une sorte d'histoire conceptuelle des interactions fecondes entre les deux disciplines au cours du XXe siecle. La premiere partie, consacree a la notion de categorie semantique et/ou syntaxique, raconte comment les theories a priori de la signification (Husserl, Frege, Russell) ont progressivement donne lieu au programme des grammaires categorielles, d'inspiration plus descriptive et empirique. La deuxieme partie traite d'un autre episode, datant des annees cinquante a soixante-dix, et lie a la naissance des grammaires generatives: celui au cours duquel l'opposition entre la these avancee par Chomsky de l'autonomie de la syntaxe, et l'idee de la priorite conceptuelle de la semantique, soutenue par des logiciens comme Montague, vient au premier plan. Enfin la troisieme partie traite des recherches tout a fait contemporaines concernant l'etude des expressions indefinies et des relations anaphoriques qu'elles soutiennent, theme ou se dessinent des convergences nouvelles entre l'analyse logique et l'analyse linguistique: la comprehension des rapports entre generalite et reference dans les langages naturels y gagnera certainement en finesse et en adequation empirique.

In this paper we relax the assumption that the logical constants of ordinary first-order logic be linearly ordered. As a consequence, we shall have formulas involving not only partially ordered quantifiers, but also partially ordered connectives. The resulting language, called the language of informational independence will be given an interpretation in terms of games of imperfect information. The II-logic will be seen to have some interesting properties: It is very natural to define in this logic two negations, weak negation as failure to verify a sentence, and strong negation as the existence of a falsifying strategy: One can express in this logic complete problems of finite structures, like the non-connectedness and 3-colorability of finite graphs, the satisfiability problem for Boolean circuits built up from NAND-gates, etc

Henkin quantifiers have been introduced in Henkin (1961). Walkoe (1970) studied basic model-theoretical properties of an extension $L_{*}^{1}$ (H) of ordinary first-order languages in which every sentence is a first-order sentence prefixed with a Henkin quantifier. In this paper we consider a generalization of Walkoe's languages: we close $L_{*}^{1}$ (H) with respect to Boolean operations, and obtain the language L¹(H). At the next level, we consider an extension $L_{*}^{2}$ (H) of L¹(H) in which every sentence is an L¹(H)-sentence prefixed with a Henkin quantifier. We repeat this construction to infinity. Using the (un)definability of truth - in - N for these languages, we show that this hierarchy does not collapse. In addition, we compare some of the present results to the ones obtained by Kripke (1975), McGee (1991), and Hintikka (1996)

The so-called New Theory of Reference (Marcus, Kripke etc.) is inspired by the insight that in modal and intensional contexts quantifiers presuppose nondescriptive unanalyzable identity criteria which do not reduce to any descriptive conditions. From this valid insight the New Theorists fallaciously move to the idea that free singular terms can exhibit a built-in direct reference and that there is even a special class of singular terms (proper names) necessarily exhibiting direct reference. This fallacious move has been encouraged by a mistaken belief in the substitutional interpretation of quantifiers, by the myth of thede re reference, and a mistaken assimilation of direct reference to ostensive (perspectival) identification. Thede dicto vs.de re contrast does not involve direct reference, being merely a matter of rule-ordering (scope).The New Theorists' thesis of the necessity of identities of directly referred-to individuals is a consequence of an unmotivated and arbitrary restriction they tacitly impose on the identification of individuals.