Home › Philosophy › Logic & Argumentation › tautology

tautology

taw-TOL-uh-jee /tɔːˈtɒl.ə.dʒi/

nounC2GRE

academicphilosophicallinguistic

A statement that is redundantly true under all possible interpretations because it repeats the same idea in different words.

In formal logic, a tautology is always true (e.g., 'It will rain tomorrow or it will not rain tomorrow'). In rhetoric, it is often criticized as empty or circular phrasing (e.g., 'free gift').

The story behind the word. Formed from Greek 'tautologia', combining 'tauto-' (the same) and 'logos' (word or reasoning). Literally 'saying the same thing twice', a tautology adds no new empirical knowledge because it merely defines itself.

Word relationships

redundancy: Redundancy refers to unnecessary words generally, while tautology specifically denotes circular logic or conceptual repetition.
pleonasm: Pleonasm is using extra words to express an idea (e.g., 'see with my eyes'), whereas tautology is repeating the logical definition.

contradiction: A contradiction is always false, whereas a tautology is always true.

Commonly confused with

oxymoron: An oxymoron combines contradictory terms ('deafening silence'), whereas a tautology combines identical meanings ('free gift').

Word family

tautological (adjective): Redundant or involving tautology.
tautologically (adverb): In a tautological manner.

Collocations

empty tautology
logical tautology
rhetorical tautology

Idioms & expressions

tautological statement

Example sentences

"Phrases like 'added bonus' or 'surrounded on all sides' are rhetorical tautologies because the adjective merely repeats the noun's core meaning." Linguistic Analysis
"The propositions of logic are tautologies; they say nothing about the empirical state of the world." Philosophical Treatise

Memory hook

TAUTO-logy = TOTAL-ly redundant talk. Saying the same thing twice in different words.

When not to use

Do not use 'tautology' for a simple contradiction or a straightforward lie; it describes something that is true to a fault, rendering it uninformative.

Fun facts

In computer programming, `x == x` or `true || false` are boolean tautologies that always evaluate to true.