User:Peter Damian/Sense and reference

See Sense and reference The distinction between sense and reference was an innovation of the German philosopher and mathematician Gottlob Frege in 1892, reflecting the two ways he believed a singular term may have meaning. Broadly the reference (or "referent") of a proper name is the object it means or indicates (German: bedeuten). The reference of a sentence is its truth value. The sense of a proper name is what the name expresses ("On Sense and Reference", Zeitschrift für Philosophie und philosophische Kritik, vol. 100 (1892) pp. 25-50, p.31), the sense of a sentence is the thought that it expresses. Frege justifies the distinction in a number of ways.

1. Sense is something possessed by an name, whether or not it has a reference. For example the name "Odysseus" is intelligible, and therefore has a sense, even though there is no individual object (its reference) to which the name corresponds.
2. Sense is wholly semantic. Reference by contrast, though semantic, is intimately connected with the named object. Frege argues that Mont Blanc "with its snowfields" cannot be a component of the thought that Mont Blanc is more than 4,000 metres high (letter to Russell). But if we find the same word in two sentences, e.g. "Etna", then we also we recognise something common to the corresponding thoughts, something corresponding to the word "Etna".
3. The sense of different names is different, even when their reference is the same. Frege that if an identity statement ("Hesperus is the same planet as Phosophorus") is to be informative, the proper names flanking the identity sign must have a different meaning or sense. But clearly, if the statement is true, they must have the same reference.

Background – Frege's early theory of meaning

Frege developed his original theory of meaning in early works like the Begriffsschrift ('concept script') of 1879 and the Grundlagen ('foundations of arithmetic') of 1884. On this theory, the meaning of a complete sentence consists in its being true or false, and the meaning of each significant expression in the sentence is an extralinguistic entity which Frege called its Bedeutung, which literally translates as 'meaning' or 'significance', but which has been rendered by Frege's translators as 'reference', 'referent', 'Meaning', 'nominatum' etc. Frege supposed that some parts of speech are complete by themselves, and are analogous to the arguments of a mathematical function, but that other parts are incomplete, and contain an empty place, by analogy with the function itself. Thus 'Caesar conquered Gaul' divides into the complete term 'Caesar', whose reference is Caesar himself, and the incomplete term '—conquered Gaul', whose reference is a Concept. Only when the empty place is filled by a proper name does the reference of the completed sentence – its truth value – appear. This early theory of meaning explains how the significance or reference of a sentence (its truth value) depends on the significance or reference of its parts.

Sense

Frege introduced the notion of Sense (German: Sinn) to accommodate difficulties in his original theory of meaning. First, if the entire significance of a sentence consists in its truth value, it follows that the sentence will have the same significance if we replace (S&R p.32) a word of the sentence with one having an identical reference, for this will not change the truth value of the sentence. If 'the evening star' has the same reference as 'the morning star', it follows that 'the evening star is a body illuminated by the Sun' has the same truth value as 'the morning star is a body illuminated by the Sun'. The reference of the whole is determined by the reference of the parts. But someone may think that the first sentence is true, but the second is false, and so the thought corresponding to the sentence cannot be its reference, but something else, which Frege called its sense. Second, sentences which contain proper names that have no reference cannot have a truth value at all. Yet the sentence 'Odysseus was set ashore at Ithaca while sound asleep' obviously has a sense, even though 'Odysseus' has no reference. The thought remains the same whether or not 'Odysseus' has a reference.