FREGE'S VENUS RIDDLE, SENSE AND REFERENCE

There’s an old philosopher’s riddle about semantics and naming known as Frege’s Puzzle, which ponders the potentially confusing reality that although 'Evenstar' and 'Morningstar' have different qualities, such as one appearing at dawn and the other at nightfall, they are in fact the same thing. The evenstar IS the morningstar, because they are both Venus.  However, you cannot always equate the two former concepts – for example if you are instructing someone when to look for the Morningstar, the instructions are different than one would give to find the Evenstar. In some senses, they are the same thing, and in others, not.

In the philosophy of language, the distinction between sense and reference was an innovation of the German philosopher and mathematician Gottlob Frege in 1892 (in his paper Über Sinn und Bedeutung), reflecting the two ways he believed a singular term may have meaning.

The reference (or "referent"; Bedeutung) of a noun or name is the object it means or indicates (bedeuten), its sense (Sinn) is what the noun expresses. The reference of a sentence is its truth value, its sense is the thought that it expresses. Frege justified the distinction in a number of ways.

1. Sense is something possessed by a 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. The sense of different names is different, even when their reference is the same. Frege argued that if an identity statement such as "the evenstar is the same planet as the morningstar" is to be informative, the nouns/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. The sense is a 'mode of presentation', which serves to illuminate only a single aspect of the referent.

Frege developed his original theory of meaning in early works like Begriffsschrift ('concept script') of 1879 and Grundlagen ('foundations') 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, literally 'meaning' or 'significance', but 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 'Julius Caesar conquered Gaul' divides into the complete term 'Julius Caesar', whose reference is JULIUS CAESAR himself, and the incomplete term '—conquered Gaul', whose reference is a Concept. Only when the empty place is filled by a noun or, like here, 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.

Frege introduced the notion of "sense" (German: Sinn) to accommodate difficulties in his early theory of meaning.

First, if the entire significance of a sentence consists of its truth value, it follows that the sentence will have the same significance if we replace a word of the sentence with one having an identical reference, as this will not change its truth value. The reference of the whole is determined by the reference of the parts. If the evenstar has the same reference as the morning star, it follows that the evenstar is a body illuminated by the Sun has the same truth value as the morning star is a body illuminated by the Sun. But it is possible for someone to think that the first sentence is true while also thinking that the second is false. Therefore, the thought corresponding to each sentence cannot be its reference, but something else, which Frege called its sense.

Second, sentences that contain nouns/names with 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. Furthermore, a thought cannot contain the objects that it is about. For example, the glaciers, or 'snowfields', cannot be a component of the thought that Mont Blanc is more than 4,000 metres high. Nor can a thought about Etna, or any other volcano, contain lumps of solidified lava.

Frege's notion of sense is somewhat obscure, and neo-Fregeans have come up with different candidates for its role. Accounts based on the work of Carnap and Church treat sense as an intension, or a function from possible worlds to extensions. For example, the intension of ‘number of planets’ is a function that maps any possible world to the number of planets in that world. John McDowell supplies cognitive and reference-determining roles. Devitt treats senses as causal-historical chains connecting names to referents. (Designation, Columbia University Press, 1981.)

The term "Frege's puzzle" is commonly applied to two related problems. One is a problem about identity statements that Frege raised at the beginning of "On Sense and Reference", and another concerns propositional attitude reports For the first problem, consider the following two sentences:

(1) Evenstar =(is) evenstar.

(2) Evenstar =(is) morning star.

Each of these sentences is true, since 'evenstar' refers to the same object as 'morning star' (the planet Venus). Nonetheless, (1) and (2) seem to differ in their meaning or what Frege called "cognitive value". (1) is just a truth of logic that can be known a priori, whereas (2) records an empirical truth that was discovered by astronomers. The problem, however, is that nouns or names are often taken to have no meaning beyond their reference (a view often associated with John Stuart Mill). But this seems to imply that the two statements mean the same thing, or have the same cognitive value.

Frege proposed to resolve this puzzle by postulating a second level of meaning besides reference in the form of what he called sense: a difference in the mode of presentation or the way an object can be "given" to us. Thus 'evenstar' and morning star' have the same reference, but differ in sense because they present Venus in different ways.

The second puzzle concerns propositional attitude reports, such as belief reports. Ordinarily, coreferring names are substitutable salva veritate, that is, without change in truth value. For example, if 'the evenstar is is bright' is true then 'The morning star is bright' is also true given that 'Evenstar' and 'Morning star' refer to one and the same planet (ie Venus). But now consider the following argument:

(3) Alex believes the evenstar is visible in the evening.

(4) Evenstar = Morning star.

(5) Alex believes the morning star visible in the evening.

This argument appears to be invalid: even if (3) and (4) are true, (5) could be false. If Alex is not aware that the evenstar and morningstar are the one and the same planet, then it seems that he could believe that the evenstar is visible in the evening while rejecting the claim that the morning star is visible in the evening (perhaps he thinks the morning star is only visible in the morning). The principle that coreferring names are substitutable salva veritate thus appears to fail in the context of belief reports (and similarly for other propositional attitude reports).

Frege again proposed to solve this problem by appeal to his distinction between sense and reference. In particular, he held that when a noun or name occurs in the context of an attitude report, its reference shifts to its ordinary sense: thus 'morning star', for example, denotes the planet Venus when it occurs in the sentence 'The morning star is visible in the evening' or in an identity sentence like (4), but when it occurs embedded in an attitude report like (5) it denotes its ordinary sense.