 Frege held two distinct theses about terms in the scope of propositional attitude verbs – that they refer to the agent’s way of representing the object and that they refer to the ordinary sense. Frege unifies these theses by maintaining that the ordinary sense is a way of representing an object. Thus he can explain the difference in truth-value between (1) and (4). Propositional attitude verbs induce a shift in reference; occurrences of expressions within their scope refer to what Frege called their customary sense. Within the scope of an attitude verb expressions refer to what they express when outside the scope of an attitude verb. So, although ‘Superman’ and ‘Clark’ are co-referring as they occur in (5) and (6), they are not in (1) and (4), when inside the scope of a propositional attitude verb.