Definition

1. Noun:
   • Useless repetition in language: A tautology is the unnecessary repetition of the same idea in different words, often making a statement redundant or empty of meaning.
   • A necessarily true logical statement: In logic, a tautology is a compound statement that is true in every possible interpretation, due to its logical form.

Examples of Usage

• As useless repetition:
  • "Free gift" is considered a tautology because a gift is, by definition, free.
  • The phrase "future plans" is a common tautology in everyday speech.
• As a logical truth:
  • In propositional logic, the statement "A or not A" is a classic example of a tautology.
  • The truth table proves that the formula is a tautology, as its value is always true.

Advanced Usage

• Rhetorical tautology: The use of redundant statements for emphasis or stylistic effect, though often criticized in formal writing.
  • The politician's tautological promise to "create new innovations" was noted by the press.
• Tautological definition: A definition that repeats the term being defined within the definition itself, offering no new information.
  • Defining "philosophy" as "the study of philosophical questions" is a tautological definition.

Variants and Related Words

• Tautological (adj): Characterized by tautology; redundant.
  • His argument was tautological and therefore unconvincing.
• Tautologically (adv): In a tautological manner.
  • The sentence is tautologically constructed.

Synonyms

• Redundancy: The state of being not or no longer needed or useful; superfluous repetition.
• Pleonasm: The use of more words than are necessary to convey meaning (e.g., "see with one's eyes").
• Truism: A statement that is obviously true and says nothing new or interesting.

Related Phrases and Idioms

• "A tautology is true by definition": A phrase used to describe the inherent truth of a logical tautology.
  • You cannot argue against it; it's a tautology, true by definition.

Noun

1. useless repetition
   • to say that something is `adequate enough' is a tautology
2. (logic) a statement that is necessarily true
   • the statement `he is brave or he is not brave' is a tautology