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In philosophy and logic, a deflationary theory of truth is one of a family of theories that all have in common the claim that assertions of predicate truth of a statement do not attribute a property called "truth" to such a statement. ==Redundancy theory== (詳細はGottlob Frege was probably the first philosophical logician to express something very close to the idea that the predicate "is true" does not express anything above and beyond the statement to which it is attributed.
Nevertheless, the first serious attempt at the formulation of a theory of truth which attempted to systematically define the truth predicate out of existence is attributable to F.P. Ramsey. Ramsey argued, against the prevailing currents of the times, that not only was it not necessary to construct a theory of truth on the foundation of a prior theory of meaning (or mental content) but that once a theory of content had been successfully formulated, it would become obvious that there was no further need for a theory of truth, since the truth predicate would be demonstrated to be redundant. Hence, his particular version of deflationism is commonly referred to as the ''redundancy theory''. Ramsey noted that in ordinary contexts in which we attribute truth to a proposition directly, as in "It is true that Caesar was murdered", the predicate "is true" does not seem to be doing any work. "It is true that Caesar was murdered" just means "Caesar was murdered" and "It is false that Caesar was murdered" just means that "Caesar was not murdered". Ramsey recognized that the simple elimination of the truth-predicate from all statements in which it is used in ordinary language was not the way to go about attempting to construct a comprehensive theory of truth. For example, take the sentence ''Everything that John says is true''. This can be easily translated into the formal sentence with variables ranging over propositions ''For all P, if John says P, then P is true.'' But attempting to directly eliminate "is true" from this sentence, on the standard first-order interpretation of quantification in terms of objects, would result in the ungrammatical formulation ''For all P, if John says P, then P.'' It is ungrammatical because P must, in that case, be replaced by the name of an ''object'' and not a proposition. Ramsey's approach was to suggest that such sentences as "He is always right" could be expressed in terms of relations: "For all ''a'', ''R'' and ''b'', if he asserts ''aRb'', then ''aRb''". Ramsey also noticed that, although his paraphrasings and definitions could be easily rendered in logical symbolism, the more fundamental problem was that, in ordinary English, the elimination of the truth-predicate in a phrase such as ''Everything John says is true'' would result in something like "If John says something, then ''that''". Ramsey attributed this to a defect in natural language, suggesting that such ''pro-sentences'' as "that" and "what" were being treated as if they were pronouns. This "gives rise to artificial problems as to the nature of truth, which disappear at once when they are expressed in logical symbolism..." According to Ramsey, it is only because natural languages lack, what he called, ''pro-sentences'' (expressions that stand in relation to sentences as pronouns stand to nouns) that the truth predicate cannot be defined away in all contexts. A.J. Ayer took Ramsey's idea one step further by declaring that the redundancy of the truth predicate implies that there is no such ''property'' as truth. There are sentences...in which the word "truth" seems to stand for something real; and this leads the speculative philosopher to enquire what this "something" is. Naturally he fails to obtain a satisfactory answer, since his question is illegitimate. For our analysis has shown that the word "truth" does not stand for anything, in the way which such a question requires. This extreme version of deflationism has often been called the ''disappearance theory'' or the ''no truth'' theory of truth and it is easy to understand why, since Ayer seems here to be claiming both that the ''predicate'' "is true" is redundant (and therefore unnecessary) and ''also'' that there is no such ''property'' as truth to speak of. 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「Deflationary theory of truth」の詳細全文を読む スポンサード リンク
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