tautology

n., pl., -gies.

1. 1. Needless repetition of the same sense in different words; redundancy.
   2. An instance of such repetition.
2. Logic. An empty or vacuous statement composed of simpler statements in a fashion that makes it logically true whether the simpler statements are factually true or false; for example, the statement Either it will rain tomorrow or it will not rain tomorrow.

[Late Latin tautologia, from Greek tautologiā, from tautologos, redundant : tauto-, tauto- + logos, saying; see -logy.]

tautological tau'to·log'i·cal (tôt'l-ŏj'ĭ-kəl) or tau'to·log'ic (-ĭk) adj.
tautologically tau'to·log'i·cal·ly adv.

For more information on tautology, visit Britannica.com.

Thanks to an Australian computer programmer, Neil Armstrong will not go down in history as having marred man's first words on the moon with a tautology about man's first step on the moon. The missing "a" was found and the famous quote was proved to be "One small step for a man...":

"The question of whether Armstrong fluffed the first lines from the surface of the moon has dogged him for the past 37 years. Sticklers for grammar point out that 'One small step for man, one giant leap for mankind' was tautology on a grand scale."

Link: Armstrong got moon script right | The Australian

Posted October 4, 2006.

See our Word Overheard blog to see interesting uses of strange words.

Technically, a formula of the propositional calculus that is true whatever the truth-value assigned to its constituent propositional variables. (A tautology is thus valid, or true in all interpretations.) In more informal contexts a tautology is often thought of as a proposition that ‘says nothing’, or merely repeats a definition.

In logic, saying the same thing in a different way, often unwittingly. For example, 'A fair-haired blonde' is tautologous if 'fair-haired' and 'blonde' are taken to have the same meanings. But if 'blonde' means the natural hair colour, then a dark-haired girl who is fair because her hair is dyed fair could be fair but not a blonde, and then 'fair-haired blonde' is not a tautology. Tautology always depends on accepted definitions.

When black, swanlike birds were discovered in Australia, there was doubt as to whether they could be 'swans' — for swans were supposed to be white. But it was allowed that though black they were swans — so 'black swan' was no longer contradictory. Conversely, it is not now tautologous to call a swan white — though it would be if the quality of whiteness was part of the definition of a swan.

(Published 1987)

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needless repetition of an idea, statement or word; a redundant (tautologous) statement

The unnecessary and excessive repetition of the same idea in different words in the same sentence, as "The room was completely dark and had no illumination," or "A breeze greeted the dusk and nightfall was heralded by a gentle wind."

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Dansk (Danish)
n. - tautologi

Nederlands (Dutch)
tautologie

Français (French)
n. - tautologie

Deutsch (German)
n. - Tautologie, Doppelaussage

Ελληνική (Greek)
n. - ταυτολογία

Italiano (Italian)
tautologia

Português (Portuguese)
n. - tautologia (f)

Русский (Russian)
применение двух различных слов для определения той же вещи, тавтология

Español (Spanish)
n. - tautología

Svenska (Swedish)
n. - tautologi, onödig upprepning

中文（简体）(Chinese (Simplified))
同义反复, 重复

中文（繁體）(Chinese (Traditional))
n. - 同義反復, 重復

한국어 (Korean)
n. - 동의어 반복, 반복, 항진식

日本語 (Japanese)
n. - 同語反復, 重複語

العربيه (Arabic)
‏(الاسم) ألحشو‏

עברית (Hebrew)
n. - ‮אמירה של אותו דבר פעמיים רצופות במלים אחרות, עודף מלים, ייתור לשון, היגד נכון בהכרח‬

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