  Schiffer argues, in effect, that given our proposition-talk and thought, propositions are, in D. M. Armstrong’s phrase, a kind of “ontological free lunch.” That is, the key “axioms” of our proposition-talk and thought are guaranteed to be true. These include the instances of the equivalence schema (E) for propositions: The proposition that p is true iff p. Given the truth of such axioms, it follows that propositions exist and have the features attributed to them by our axioms. Moreover, because these axioms are constitutive of the concept of a proposition, it follows that, by possessing that concept, we can know the truth of these axioms.