 First, it seems difficult to sort propositions into distinct kinds according to the subject matter they are about. Take, e.g., the proposition that killing is morally wrong, or the proposition that immoral acts happen in space-time. What are they about? Intuitively, their subject matter is mixed, belonging to the physical domain, the biological domain, and the domain of ethical discourse. It is hard to see how pluralism can account for the truth of such mixed propositions, belonging to more than one domain of discourse: What will be the realizing property?