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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 ?
But it is an objective condition without a content-lack is the predicate of the verb "to lack" and becomes tautologous.
Culture, having been co-opted into the complete commodification of society, is no longer in a position to remedy or criticise itself, and philosophy, insofar as it is not doing so, will remain an irrelevant, and often tautologous, aside.
Childers (Erskine's Gladstonian father), Fordham concludes that the conflict between particularism and universalism mapped in the novel 'reflects the British Empire collapsing under the weight of its own particular tautologous, desperate, and finally failing universalization of its subject' (pp.
Given this form, it becomes tautologous to say that 'all' descriptions are cases of predications or attributions of the predicate y to the name x which stands for an object-thing-event in the extensional world.
SIR - Brian Davies wonders why the media, not to mention the rest of us, use the tautologous term headbutt when just butt will do (Western Mail, Letters, July 15).
Indeed, nearly half of his book demonstrates with rigor and candor why scientific models yielding worst-case-scenario predictions for environmental catastrophe are uncertain, unverifiable, oversimplified and tautologous.
That it is pompous and dull, even tautologous, need not concern us.
The first claim is tautologous and hardly worth mentioning, except for the fact that many people and their communities routinely ignore its truth.
The limitation of Frank's second definition of demoralization is its sheer breadth and a tendency toward the tautologous.