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Consider the English sentence, 'Elephants are animals' is true. It is obvious that this sentence is true if and only if the complimentary sentence, Elephants are animals, is true. Thus, the truth values of these two sentences are always the same, under an y possible interpretation. According to the redundancy theory, this implies the two sentences mean the same, i. e. the predicate '...is true' in the first sentence is meaningless.
Along the same lines, according to the redundancy theory, if A says something, and B replies, That's true, all he does is repeat A's statement, for '...is true' again is redundant, as in the first example.
With so-called blind uses of truth, that is when somebody ascribes truth to a statement which is not being mentioned but referred to by indirect reference only, as in What John says is true, one cannot claim that '...is true' is as redundant as in the abo ve examples, for an incomplete utterance such as What John says would not make any sense. Ramsey is aware of this problem, and he suggests re-phrasing such utterances as "For any utterance p, if John asserts p, then p" (paraphrase from: F. P. Ramsey, Fact s and Propositions; reprinted in: Pitcher, Truth, p. 17). This is one way of eliminating the words '...is true' from such sentences.
Now, as Ramsey has shown, it seems to be possible to get rid of the words '...is true' in any English sentence without affecting the conditions under which the sentence would be true. To Ramsey, this implies that any meaning we associate with the predicat e '...is true' is a linguistic illusion, and in particular, the noun 'truth' cannot refer to anything. Thus, there is no way of explaining what 'truth' is, which would be an obvious reason why philosophers have been unable to agree on any of the theories of truth proposed earlier.
But there is another influential theory, called the performative theory of truth, which claims that, although utterances such as That is true do not actually mean anything different from the statement they refer to, the speaker does, however, perform a ce rtain action of endorsement or agreement with the person whose statement he asserts. Thus, the predicate '...is true' is not seen as totally redundant, only as redundant with respect to its meaningful content. Reverting to a previous example, this theory might be formalised as "As John stated, p" (paraphrase from: Johnson, Focusing on Truth, p. 79).
Opponents of the redundancy theory complain that redundancy theorists "only sweep the problem [of truth] under the rug" (Johnson, ibid., p.255). They point out that if two different statements are true and false together, this does not necessarily say the y are equivalent in meaning. Thus, there may well be more to truth than the features covered by the redundancy theory, and accepting this theory might mean that we remain unaware of the underlying character of truth. As a riposte to the above argument in favour of the redundancy theory, its opponents maintain that, with matters concerning truth, arguing on the grounds of truth-equivalence may be rather too close to begging the question (Johnson, ibid., p. 74)
Firstly, it seems that the redundancy theory of truth does actually consist of several separate explanations, depending on the context of the words '...is true'. There is one theory for explicitly stated sentences, such as John says that elephants are ani mals, and that is true, and an entirely different one for implicit truth ascriptions, as in What John says is true. Does this imply there are in fact two theories of redundancy, or does the predicate '... is true' have a distinct meaning, after all, namel y that of picking out the applicable method of explaining truth?
In response to this challenge, Srzednicki suggests using a transcription such as "For all p, if John just asserted p, then p" (paraphrase from: Kirkham, ibid., p. 320). This interpretation unifies the two distinct cases outlined above.
Secondly, however, and with especial regard to the implicit case of statements involving truth: How does the quantification in For all p, if John asserts p, then p work? Does a speaker have to be aware of all possible statements p when making such a gener al claim pertaining to his confidence in the truth of John's utterances?
And thirdly, it remains impossible to consolidate the two different interpretations of the redundancy theory for explicit and implicit statements, respectively. If one tries to render the implicit usage of truth ascription in a form analogous to the expli cit transformation, i. e. by simply removing the redundant parts, the resulting expressions, for example John says that, do not form complete sentences and hence cannot preserve the meaning. On the other hand, if one starts formulating the explicit cases by quantifying in a fashion similar to the formula for implicit statements, there is no predicate which could correspond to John asserts p, but such a predicate is necessary for picking out just the one statement under consideration. Thus, it seems one ca nnot maintain that the predicate '...is true' is entirely without meaning, as it must refer to this process of picking the appropriate interpretation, in the least.
Finally, by frankly denying the issue of truth, the redundancy theory disallows any possible relation between two different statements, even if they mean the same. Usually, there is more than only one way of expressing the same meaning, and accordingly, t hose statements should be true or false together. The redundancy theory, however, does not offer any possibility of establishing a relation of whatever nature between different statements.
Furthermore, one always needs a predicate to complete an English sentence, and the advocates of the redundancy theory of truth argue that, sometimes, it seems '...is true' takes the function of a dummy predicate without any meaning of its own. These philo sophers claim that, analogous to the usage of 'it' in a statement such as it is raining, the predicate '...is true' may exist in the English language for just this purpose, and this could even be the cause why it is perceived as being useful.
"'Why did Brutus murder Caesar?' is a good question, whereas 'Why is it true that Brutus murdered Caesar?' is not." (White, Truth, p. 93)
Another observation that cannot be explained by the redundancy theory is, why is it only assertive utterances that we can call 'true'? If to say That's true is agreement with a previous speaker, or even a simple repetition of what has been said, why shoul d it be impossible to express endorsement of a suggestion, like Would you mind closing the window?, by the same words, That's true? (cf. White, ibid., p. 100)