 It is a controversial matter whether Quine was right to demand such rigorous criteria of identity as a condition for acceptance of a class of entities.  However, even if Quine asks too much, any good theory of propositions ought to have something to say about when propositions are identical and when they are distinct.  Developing theories which give such accounts in a way that fits well with intuitive data concerning propositional attitude ascriptions would enhance our reasons to accept propositions. 