LANGUAGE Let us assume for the time being that the sentence has reference If we now replace one word of the sentence by another having the same reference, but a different sense, this can have no bearing upon the reference of the sentence Yet we can see that in such a case the thought changes; since e.g the thought in the sentence ‘The morning star is a body illuminated by the Sun’ differs from that in the sentence ‘The evening star is a body illuminated by the Sun’ Anybody who did not know that the evening star is the morning star might hold the one thought to be true, the other false The thought, accordingly, cannot be the reference of the sentence, but must rather be considered as the sense (CP 162) If the thought expressed by a sentence is not its reference, does the sentence have a reference at all? Frege agrees that there can be sentences lacking reference: sentences occurring in works of fiction such as the Odyssey But the reason these sentences lack a reference is that they contain names that lack a reference, such as ‘Odysseus’ Other sentences have a reference; and consideration of fictional sentences will enable us to determine just what that reference is We must expect that the reference of a sentence is determined by the reference of the parts of a sentence Let us inquire, therefore, what is missing from a sentence if one of its parts lacks a reference If a name lacks a reference, that does not affect the thought, since that is determined only by the sense of its constituent parts, not by their reference It is only if we treat the Odyssey as science rather than myth, if we want seriously to take the sentences it contains as true or false, that we need to ascribe a reference to ‘Odysseus’ ‘Why we want every proper name to have not only a sense, but also a reference? Why is the thought not enough for us? Because, and to the extent that, we are concerned with its truth-value’ (CP 163) We are, Frege says, driven into accepting as the reference of a sentence its truthvalue, the True, or as the case may be, the False Every seriously propounded indicative sentence is a name of one or other of these objects All true sentences have the same reference as each other, and so all false sentences The relation, then, between a sentence and its truth-value is the same as that between a name and its reference This is a surprising conclusion: surely, to assert that pigs have wings is to something quite different from naming anything Frege would agree; but that is because asserting a sentence is something quite different from putting a sentence together out of subject and predicate ‘Subject and predicate (understood in the logical 123