  The impossibility theorem of Dekel, Lipman and Rustichini has been thought to
demonstrate that standard state-space models cannot be used to represent
unawareness. We first show that Dekel, Lipman and Rustichini do not establish
this claim. We then distinguish three notions of awareness, and argue that
although one of them may not be adequately modeled using standard state spaces,
there is no reason to think that standard state spaces cannot provide models of
the other two notions. In fact, standard space models of these forms of
awareness are attractively simple. They allow us to prove completeness and
decidability results with ease, to carry over standard techniques from decision
theory, and to add propositional quantifiers straightforwardly.
