According to the Millian-Russellian, (17) and (18) differ only in the substitution of expressions with have the same content: after all, “Clark Kent” and “Superman” are proper names which refer to the same object, and the Millian-Russellian holds that the content of a proper name is the object to which that name refers. But this is a surprising result. These sentences seem to differ in meaning, because (17) seems to express a trivial, obvious claim, whereas (18) seems to express a non-trivial, p