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The theory of descriptions is the philosopher Bertrand Russell's most significant contribution to the philosophy of language. It is also known as Russell's Theory of Descriptions (commonly abbreviated as ''RTD''). In short, Russell argued that the syntactic form of descriptions (phrases that took the form of "The aardvark" and "An aardvark") is misleading, as it does not correlate their logical and/or semantic architecture. While descriptions may seem fairly uncontroversial phrases, Russell argued that providing a satisfactory analysis of the linguistic and logical properties of a description is vital to clarity in important philosophical debates, particularly in semantic arguments, epistemology and metaphysics. It has been argued, for example, that RTD largely underpinned Russell's theory of sense-data. Since the first development of the theory in Russell's 1905 paper "On Denoting", RTD has been hugely influential and well-received within the philosophy of language. However, it has not been without its critics. In particular, the philosophers P. F. Strawson and Keith Donnellan have given notable, well known criticisms of the theory. Most recently, RTD has been defended by various philosophers and even developed in promising ways to bring it into harmony with generative grammar in Noam Chomsky's sense, particularly by Stephen Neale. Such developments have themselves been criticised, and debate continues. ==Introduction== Bertrand Russell's theory of descriptions was initially put forth in his 1905 essay "On Denoting", published in the journal of philosophy ''Mind''. Russell's theory is focused on the logical form of expressions involving denoting phrases, which he divides into three groups: # Denoting phrases which do not denote anything, for example "the current Emperor of Kentucky". # Phrases which denote one definite object, for example "the present President of the U.S.A." We need not know which object the phrase refers to for it to be unambiguous, for example "the cutest kitten" is a unique individual but his or her actual identity is unknown. # Phrases which denote ambiguously, for example, "an Aardvark". ''Indefinite descriptions'' constitute Russell's third group. Descriptions most frequently appear in the standard subject-predicate form. Russell put forward his theory of descriptions to solve a number of problems in the philosophy of language. The two major problems are (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 seen at different times of day (indeed, they are both the planet Venus: the morning star is the planet Venus seen in the morning sky and the evening star is the planet Venus seen in the evening sky), how is it that someone can think that the morning star rises in the morning but the evening star does not? 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 identical or synonymous expressions. The problem of non-referring expressions is that certain expressions that are meaningful do not truly refer to anything. For example, by "any dog is annoying" it is not meant that there is a particular individual dog, namely ''any dog'', that has the property of being annoying (similar considerations go for "some dog", "every dog", "a dog", and so on). Likewise, by "the current Emperor of Kentucky is gray" it is not meant that there is some individual, namely ''the current Emperor of Kentucky '', who has the property of being gray; Kentucky was never a monarchy, so there is currently no Emperor. 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 current Emperor of Kentucky is gray" or "it is not the case that the current Emperor of Kentucky is gray". 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 Emperor of Kentucky. So, since the subject does not exist, it is not in the extension of either predicate (it is not on the list of gray people or non-gray 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「theory of descriptions」の詳細全文を読む スポンサード リンク
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