Unawareness and partitional information structures

We claim first that simple uncertainty is not an adequate model of a subjec t's ignorance, because a major component of it is the inability to give a c omplete description of the states of the world, and we provide a formal mod el of unawareness. In Modica and Rustichini (1994) we showed a difficulty i n the project, namely that without weakening of the inference rules of the logic one would face the unpleasant alternative between full awareness and full unawareness. In this paper we study a logical system where non full aw areness is possible, and prove that a satisfactory solution to the problem can be found by introducing limited reasoning ability of the subject. A det ermination theorem for this system is proved, and the appearance of partiti onal informational structures with unawareness is analysed. (C) 1999 Academ ic Press.