 The Fregean theory is motivated in part by the same considerations that motivate analogous views in the philosophy of language. The key sort of example in the philosophy of language involves a pair of sentences, such as “Hesperus is the morning star” and “Hesperus is the evening star”, that are the same except for containing different terms that refer to or denote the same thing (both “the morning star” and “the evening star” denote Venus). Suppose a subject rationally accepts one of these sentences while rationally rejecting or remaining neutral on the other. Then, it is argued, though the sentences cannot differ in their truth-value, they must play different roles in the subject’s reasoning: for example, the subject will list Hesperus among the heavenly bodies visible in the evening, but she won’t list Hesperus among the heavenly bodies visible in the morning. Fregean theorists take there to be an aspect of meaning that is linked to cognitive role in this way.