TAUTOLOGY: Word of the Day - November 10, 2005

tautology (n.)

Pronunciation: tô-tŏl'ə-jē (stress on middle syllable)

Definition: 1. Needless repetition of the same sense in different words; redundancy; an instance of such a repetition. 2. Logic An empty or vacuous statement composed of similar statements in a fashion that makes it logically true whether the simpler statements are factually true or false; for example, "Either it will rain tomorrow or it will not rain tomorrow." (This definition comes from dictionary.com and yourdictionary.com, so that is the definition out there for the public)

It's Greek to me. And to you. And to anyone, really.

But it's also Latin. Things just trickle from one language to another before they get to us, transmuted. The Greek roots are tauto- "the same" and logos "saying," which is related to legein, meaning "to say" (lecture comes from that). The Latin word is tautologia (representation of the same thing).

It should be noted that, strictly speaking, a tautology is a logical term that corresponds to statements that are true by their own definition. That is, a statement is tautological if it is true regardless of the truth of its parts. For example, I could say, "If a prime number is even and bigger than two, then it must be divisible by three" and it would be true. Unfortunately, there are no even prime numbers greater than two, so the statement is excessively superfluous (HA HA HA!) All true statements of logic are tautologies. Though not all false statements of logic are not tautologies. In fact, quite a few of them are. It has come to mean, outside of logic and in grammar, useless, uninformative repetition. If I had said, "All true statements of logic are tautologies and all false statements are not tautologies," that would have been a grammatical tautology, but a logical fallacy.

Wikipedia tells me that tautologies are often used to introduce a red herring, or an ignoratio elenchi, into argument. An ignoratio elenchi (irrelevant conclusion) is a logical fallacy which presents an argument that may itself be valid, but which proves or supports a different proposition than the one it is purporting to prove or support.

I'd be lying if I said teaching wasn't tautological. And I'd be telling the truth if I said teaching is tautological.

Ah! An example of grammatical tautology and logical tautology. There's a subtle fallacy here, which introduces an ignoratio elenchi. If I say, "Teaching is not tautological" and I have furthermore informed you that that is a lie, it does not necessarily make the statement "Teaching is tautological" truthful.

I stumbled upon that. Cool.

Nick, tautologies are apparently very useful for mathematics; as are vacuous truths (get back to me about the empty product). Incidentally, the mathematical symbol for a tautology is .

Tautological expressions include: ATM machine (automated teller machine machine), PIN number (personal identification number number), add an additional, added bonus, climb up, close scrutiny, combine together, comprises of, first began, passing fad, specific details, unintentional mistake, etc.