forthcoming in the Proceedings of the International Conference Computers and Philosophy organized by Colin Schmidt at Laval (France) in May 2006 BELIEF AND DESIRE: A LOGICAL ANALYSIS

Propositional attitudes directed at facts of the world are cognitive or volitive. Cognitive attitudes contain beliefs and volitive attitudes desires. Beliefs are satisfied whenever they are true and desires whenever they are realized. The main purpose of this paper is to analyze the logical form of such primitive kinds of attitudes and to explicate their conditions of possession and of satisfaction. According to standard epistemic logic human agents are either perfectly rational or totally irrational. I will advocate an intermediate position compatible with philosophy of mind and psychology according to which agents are minimally rational. They can be inconsistent but they never are entirely irrational. In order to account for the imperfect but minimal rationality of human agents I will explicate both subjective and objective possibilities in the logic of attitudes. For that purpose, I will exploit the resources of a non classical propositional predicative logic that distinguishes propositions with the same truth conditions that do not have the same cognitive value. In my approach, the relations of compatibility with the satisfaction of agents’ beliefs and desires are also explicated in a finer way so as to avoid current epistemic and volitive paradoxes. I will use both proofand model-theory in order to formulate my logic of belief and desire. At the end I will enumerate important valid laws governing such attitudes. As Descartes pointed out in his treatise on Les passions de l’âme, beliefs and desires are primitive kinds of attitudes. Every propositional attitude is cognitive or volitive. All cognitive attitudes (e.g. conviction, faith, confidence, knowledge, certainty, presumption, pride, arrogance, surprise, amazement, stupefaction, prevision, anticipation, expectation) contain beliefs. Similarly, all volitive attitudes (e.g. wish, will, intention, ambition, project, hope, aspiration, satisfaction, pleasure, enjoyment, delight, gladness, joy, elation, amusement, fear, regret, sadness, sorrow, grief, remorse, terror) contain desires. So beliefs and desires are essential components of all propositional attitudes. The main purpose of this chapter is to analyze their logical form. 1 I am grateful to Hugolin Bergier, David Kaplan, Kenneth MacQueen and John Searle for critical remarks on a first draft of this paper. 2 The treatise Les passions de l’âme is reedited in R. Descartes Œuvres complètes La Pléiade Gallimard 1953