Sense and reference

The distinction between sense and reference was introduced by the German philosopher and mathematician Gottlob Frege in 1892, in his paper "On Sense and Reference" (German: "Über Sinn und Bedeutung"). According to Frege, a linguistic expression has two aspects: its reference, which is the object it designates or refers to, and its sense, which is what the expression expresses, that is, the mode in which that object is presented.

The distinction grew out of problems in the theory of meaning that Frege had developed in earlier works such as the Begriffsschrift (1879) and The Foundations of Arithmetic (1884). In that first theory, the meaning of each significant expression was its reference, and the truth value of a sentence depended on the reference of its parts. Frege noticed two difficulties. First, if two expressions share a reference, substituting one for the other does not change a sentence's truth value, yet a person may believe one sentence true and the other false, so the thought a sentence expresses cannot simply be its reference. Second, sentences containing proper names without referents, such as those about Odysseus, seem to have a sense even though they lack a truth value. Sense was meant to solve both problems.

Frege offered several arguments for the distinction. A name can have a sense without having a referent, as with the description "the largest integer", which is intelligible although it designates nothing. Moreover, two different names with the same reference can have different senses: if "Hesperus is the same planet as Phosphorus" is informative, the two names cannot share a sense, even though both designate the same heavenly body. Sense thus works as a mode of presentation that illuminates only one aspect of its referent.

In the reading of many later authors, sense has been understood as a description, in line with Bertrand Russell's theory of descriptions, which held that many proper names are disguised definite descriptions. However, Michael Dummett, Gareth Evans and John McDowell have argued that this descriptivist reading does not faithfully represent Frege's view. Saul Kripke, for his part, criticized the idea that proper names are equivalent to descriptions, arguing that they are rigid designators. Today the concept remains central to the philosophy of language and logic, and its candidate explanations, such as Carnap and Church's intensions, McDowell's cognitive roles, or Devitt's causal-historical chains, are still debated.