Alternative Semantics for Unawareness

Modica and Rustichini [1994] provided a logic for reasoning about knowledge where agents may be unaware of certain propositions. However, their original approach had the unpleasant property that nontrivial unawareness was incompatible with partitional information structures. More recently, Modica and Rustichini [1999] have provided an approach that allows for nontrivial unawareness in partitional information structures. Here it is shown that their approach can be viewed as a special case of a general approach to unawareness considered by Fagin and Halpern [1988]. Journal of Economic Literature Classification Numbers: D80, D83.