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Logic a statement that is always true, esp a truth-functional expression that takes the value true for all combinations of values of its components, as in either the sun is out or the sun is not out



(1) The repetition of the same word or of words close in meaning: also, an example of such repetition. Examples are iasnee iasnogo (“completely obvious”; literally, “clearer than clear”) and plachet, slezami zalivaetsia (“she weeps, dissolved in tears”). In poetic language, especially in oral folk poetry, tautology is used to intensify emotional effect. An example in the bylina (epic folk song) about Nightingale the Robber is Pod Chernigovom silushki chernym-cherno, I Chernym-cherno, chernei vorona (“Near Chernigov the troops looked black as could be [literally, ‘black-black’], / Black as could be, blacker than a raven”). Poets often use tautology and tautological rhymes; an example is Pushkin’s Vot na bereg vyshli gosti, / Tsar’ Saltan zovet ikh v gosti (“The visitors disembarked, / Tsar Saltan invited them to visit”).

A number of tautological word groups are widely used in colloquial speech, for example, tselikom i polnost’iu (“wholly and completely”), k segodniashnemu dniu (“by today”; literally, “by today’s day”) and den’-den’skoi (“the livelong day”). Unnecessary repetitions in speech sometimes testify to a speaker’s limited command of language. Tautology is a type of pleonasm.


(2) In logic, an extreme example of the logical fallacy of the unwarranted premise (Latin petitio principii), namely, the definition or proof of something by the same thing (Latin idem per idem). In two-valued classical logic the term “tautology,” like the term “law of logic,” refers to reliable, always true, or identically true formulas that remain constant in relation to their constituent variables, that is, in relation to the world’s actual state of affairs. In this type of logic, according to G. W. von Leibniz, tautologies are truths in all possible worlds, eternal truths, essential truths, and truths by virtue of the postulates of classical logic. An example of this type of tautology is the law of the excluded middle.

In many-valued logic, a tautology is a formula which in any set from an accepted universal system of values for variables retains the same distinctive value. This type of tautology is used in proofs of independence.


Wittgenstein, L. Logiko-filosofskii traktat. Moscow, 1958. (Translated from German.)
Church, A. Vvedenie v matematicheskuiu logiku, vol. 1. Moscow, 1960. (Translated from English.)



A proposition which is always true.

Compare: paradox.

The Linguistic Smarandache Tautologies,.
References in periodicals archive ?
Against the view of Eric D'Arcy and others, who see the first principle of the practical order ("do good, avoid evil") as merely formal or tautologous, McInerny holds that the first principle is both descriptive and prescriptive.
Connor goes on to hint at the possibly tautologous nature of this relationship, and explains it in terms of institutional exigencies: that postmodernism, in the form in which it is understood in literature departments, 'serves to concentrate radical or sceptical theory into an institutionally usable form, allowing the business of the literary academy -- the interpretation of texts, the production and accreditation of readings and methodologies -- to go on as usual'.
On initial consideration, IrP may seem almost tautologous.
As a defense of utility-based ethical calculation this is tautologous and adds little to the discussion.
Though Strasser does not explore this distinction, he allows for this kind of account--the second understanding of a dominant desire he considers is meant to capture all such accounts that do not make it tautologous that an agent will pursue whatever her strongest desire is.
Similarly, ostensible dialogues are really monologues; their repetitious self-enclosure matches the colors' continual tautologous self-identity.
As indicated, the rational choice paradigm, boiling down to utility maximization, is of dubious validity even in the economic realm, where most processes and relations are social rather than natural or technical in character, and a fortiori appears speculative and tautologous when applied outside the narrow terrain of markets and prices.
Incipit fiber Enchiriadis de musica', the best-attested title, makes sense on these assumptions, even if `the book of the handbook' seems tautologous.
Conversely, too great a flexibility on this matter entails the risk of simply labelling the activities of headquarters management as strategic and those of site managers as operational - which is tautologous.
26) Consequently, I think that both scutum gladiumque relinques/ et iaculum et galeam (all of 123b-4a) and spoliatis arma supersunt (124b) are `excellent in themselves': the only real difficulty is that they are deplorably tautologous as juxtaposed.
Any such sentence would presumably be not only true but tautologous (in the vernacular sense); but whether or not a sentence is tautologous is ostensibly a function solely of its form--whence, if any sentences of the form a is a are tautologous they all are, (10) included.
Bloch says that the jongleur in the fabliau "Le Roy d'Angleterre et le jongleur d'Ely," who deflects the king's questions about his origins, identity, and destination by pretending to misunderstand them and by giving tautologous, uninformative replies, "is aware that 'sense' and 'good sense' (sen and saver) are the conditions of the courtly and noble life and that madness or a lack of sense is - beyond any overtly radical social gesture - a condition of poetry, if not of all linguistic expression" (16).