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Theory of descriptions

The theory of descriptions is one of the philosopher Bertrand Russell's most significant contributions to the philosophy of language. It is also termed Russell's Theory of Descriptions (often abbreviated as RTD). In short, Russell argued that the superficial syntactic form of descriptions (phrases usually of the form "The X" and "An X") is misleading, as it does not match their logical or semantic structure. While descriptions may seem fairly insignificant phrases, Russell and others have argued that providing a satisfactory analysis of their linguistic and logical properties is vital to clarity in important philosophical debates, particularly in semantics, epistemology and metaphysics. It has been argued, for example, that RTD largely underpinned Russell's theory of sense-data.

Since the initial development of the view in Russell's 1905 paper "On Denoting", RTD has been highly influential and well-received among many philosophers. However, it has not been without criticism. In particular, the philosophers P. F. Strawson and Keith Donnellan have given notable criticisms of the theory. More recently, RTD has been defended and developed in promising ways to harmonize with generative grammar in Noam Chomsky's sense, particularly by Stephen Neale. Such developments have themselves been criticized, and debate continues.

Russell's theory of descriptions was most clearly expressed in his 1905 essay "On Denoting", published in the philosophy journal Mind. Russell's theory is about the logical form of expressions involving denoting phrases, which he divides into three groups:

1. Denoting phrases which do not denote anything, for example "the present King of France".
2. Phrases which denote one definite object, for example "the present King of England" (Edward VII at the time Russell was writing). We need not know which object the phrase refers to for it to be unambiguous, for example "the tallest spy" is a unique individual but his or her actual identity is unknown).
3. Phrases which denote ambiguously, for example, "a man".

Definite descriptions involve Russell's second group of denoting phrases, and indefinite descriptions involve Russell's third group. Descriptions typically appear to be of the standard subject-predicate form. Russell proposed his theory of descriptions in order to solve several problems in the philosophy of language. The two major problems are of (1) co-referring expressions and (2) non-referring expressions. The problem of co-referring expressions originated primarily with Gottlob Frege as the problem of informative identities. For example, if the morning star and the evening star are the same planet in the sky (indeed they are), how is it that someone can think that the morning star rises in the morning but the evening star does not? That is, someone might find it surprising that the two names refer to the same thing (i.e. the identity is informative). This is apparently problematic because although the two expressions seem to denote the same thing, one cannot substitute one for the other, which one ought to be able to do with identitical or synonymous expressions.

The problem of non-referring expressions is that certain expressions that are meaningful do not seem to refer to anything. For example, by "any man is sexist" it is not meant that there is a particular individual, namely any man, that has the property of being sexist (similar considerations go for "some man", "every man", "a man", and so on). Likewise, by "the present King of France is bald" it is not meant that there is some individual, namely the present King of France, who has the property of being bald (France is no longer a monarchy, so there is currently no King of France). Thus, what Russell wants to avoid is admitting mysterious non-existent entities into his ontology. Furthermore, the law of the excluded middle requires that one of the following propositions, for example, must be true: either "the present King of France is bald" or "it is not the case that the present King of France is bald". Normally, propositions of the subject-predicate form are said to be true if and only if the subject is in the extension of the predicate. But, there is currently no King of France. So, since the subject does not exist, it is not in the extension of either predicate (it is not on the list of bald people or non-bald people). Thus, it appears that this is a case in which the law of excluded middle is violated, which is also an indication that something has gone wrong. Russell says in his paper, in a typically sly dig at a school of philosophy with which he disagreed, that "Hegelians, who love a synthesis, will probably conclude that he wears a wig."