In this paper, I will develop a set of boulesic-doxastic tableau systems and prove that they are sound and complete. Boulesic-doxastic logic consists of two main parts: a boulesic part and a doxastic part. By ‘boulesic logic’ I mean ‘the logic of the will’, and by ‘doxastic logic’ I mean ‘the logic of belief’. The first part deals with ‘boulesic’ concepts, expressions, sentences, arguments and theorems. I will concentrate on two types of boulesic expression: ‘individual x wants it to be (...) the case that’ and ‘individual x accepts that it is the case that’. The second part deals with ‘doxastic’ concepts, expressions, sentences, arguments and theorems. I will concentrate on two types of doxastic expression: ‘individual x believes that’ and ‘it is imaginable to individual x that’. Boulesic-doxastic logic investigates how these concepts are related to each other. Boulesic logic is a new kind of logic. Doxastic logic has been around for a while, but the approach to this branch of logic in this paper is new. Each system is combined with modal logic with two kinds of modal operators for historical and absolute necessity and predicate logic with necessary identity and ‘possibilist’ quantifiers. I use a kind of possible world semantics to describe the systems semantically. I also sketch out how our basic language can be extended with propositional quantifiers. All the systems developed in this paper are new. (shrink)

In this paper we consider logical inference as an activity that results in proofs and hence produces knowledge. We suggest to merge the semantical analysis of deliberatively seeing-to-it-that from stit theory and the semantics of the epistemic logic with justification from. The general idea is to understand proving that A as seeing to it that a proof of A is available. We introduce a semantics of various notions of proving as an activity and present a number of valid principles that (...) relate the various notions of proving to each other and to notions of justified knowledge, implicit knowledge, and possibility. We also point out and comment upon certain principles our semantics fails to validate. (shrink)

This paper studies intentional action in stit logic. The formal logic study of intentional action appears to be new, since most logical studies of intention concern intention as a static mental state. In the formalization we distinguish three modes of acting: the objective level concerning the choices an agent objectively exercises, the subjective level concerning the choices an agent knows or believes to be exercising, and finally, the intentional level concerning the choices an agent intentionally exercises. Several axioms constraining the (...) relations between these different modes of acting will be considered and discussed. The side effect problem will be analyzed as an interaction between knowingly doing and intentionally doing. Non-successful action will be analyzed as a weakening of the epistemic attitude towards action. Finally, the notion of ‘attempt’ will be briefly considered as a further weakening in this direction. (shrink)

1. Introduction Dans l?encyclopédie Wikipedia accessible sur Internet, les thèses de Bren­tano sont résumées dans les trois phrases suivantes : L?intentionnalité est une caractéristique de la conscience. L?intentionnalité peut être caractérisée par quelques formules : « contenir quelque chose (pas forcément réel) à titre d?objet », « être à propos de quelque chose », « avoir un objet immanent ». Selon Franz Brentano, l?intentionnalité est le critère permettant de distinguer les « faits » psychiques des « faits » physiques : (...) tout fait psychique est intentionnel, c?est-à-dire qu?il contient quelque chose à titre d?objet bien que ce soit toujours d?une manière différente (croyance, jugement, perception, conscience, désir, haine, etc.). Comme le souligne Denis Seron, l?intentionnalité pour Brentano est une rela­tion, mais ce n?est pas une relation comme les autres dans la mesure où elle n?exige pas l?existence de tous ses termes [Seron 2010]. C?est pour capter cette particularité que Brentano emprunte à saint Thomas le concept d? in­existence intentionnelle [McCormick 1981]. P ar exemple, on peut penser à un objet non réel comme la planète inexistante Vulcain dont certains astro­nomes du xix e siècle avaient postulé l?existence pour expliquer les pertur­bations de l?orbite de Mercure. Il est clair qu?une relation intentionnelle comme « penser à » aura une logique à part. (shrink)