Tautology (language)

In literary criticism and rhetoric, a tautology is a statement that repeats an idea using near-synonymous morphemes, words or phrases, effectively "saying the same thing twice".^[1][2] Tautology and pleonasm are not consistently differentiated in literature.^[3] Like pleonasm, tautology is often considered a fault of style when unintentional. Intentional repetition may emphasize a thought or help the listener or reader understand a point.^[4] Sometimes logical tautologies like "Boys will be boys" are conflated with language tautologies, but a language tautology is not inherently true, while a logical tautology always is.^[4]

The word was coined in Koine Greek from ταὐτός ('the same') plus λόγος ('word' or 'idea'), and transmitted through 3rd-century Latin tautologia and French tautologie. It first appeared in English in the 16th century. The use of the term logical tautology was introduced in English by Wittgenstein in 1919, perhaps following Auguste Comte's usage in 1835.^[5]

Tautological initialisms redundantly repeat the final word of an abbreviation. Examples include "RAS syndrome", "CD disc", "ATM machine", "PIN number", and "HIV virus".^[6] Tautological phrases include "new innovation", "hot water heater", "evening sunset", "short summary", "predictions about the future", "close proximity", and "necessary requirement".^[7]

The use of tautologies is usually unintentional. For example, the phrases "mental telepathy", "planned conspiracies", and "small dwarfs" imply that there are such things as physical telepathy, spontaneous conspiracies, and giant dwarfs, which are oxymorons.^[8] Parallelism is not tautology, but rather a particular stylistic device. Much Old Testament poetry is based on parallelism: the same thing said twice, but in slightly different ways. H. W. Fowler describes this as pleonasm.^[1]