Unawareness : A Formal Theory of Unforeseen Contingencies. Part II

In this paper we conclude the research initiated in Modica and Rustichini [6]. We claim here, as we did in that paper, that simple uncertainty is not an adequate model of a subject's ignorance, because a major component of it is the inability to give a complete description of the states of the world, and we provide a formal model of unawareness. In Modica and Rustichini [6j we showed a difficulty in the project, in that without a weakening of the inference rules of the logic one would face the unpleasant alternative between full awareness and full unawareness. We give a formal definition of unawareness, we study a system of modal logic where non full awareness is possible, and prove that a satisfactory solution to the problem can be found by introducing limited reasoning ability of the subject.