RationalWiki's 2018 Fundraiser

There is no RationalWiki without you. We are a small non-profit with no staff — we are hundreds of volunteers who document pseudoscience and crankery around the world every day. We will never allow ads because we must remain independent. We cannot rely on big donors with corresponding big agendas. We are not the largest website around, but we believe we play an important role in defending truth and objectivity.

If everyone seeing this today donates $5, we will meet our goal for 2018.

Fighting pseudoscience isn't free.
We are 100% user-supported! Help and donate $5, $20 or whatever you can today with PayPal Logo.png!

Donations so far: $3383Goal: $5000

Tautology

From RationalWiki
Jump to: navigation, search
The First Rule of Tautology Club is the first rule of Tautology Club.
Tautology Club


Part of the series on
Logic and rhetoric
Icon logic.svg
Key articles
General logic
Bad logic

A tautology is a tautological statement.

But seriously[edit]

A tautology is a statement that, by virtue of logic and nothing more, is true, but in such a way that it contains no useful information: "The red bicycle is red." Sometimes this can extend beyond simple logic to obvious definitional facts: "The red bicycle has two wheels."

Sometimes tautologies are hard to extricate and identify when they are buried in masses of argumentative prose. In other situations, it may be obscured by experimental design.[1]

One particular kind of tautology is "assuming the antecedent", also known as "circular logic". This is often engaged in by bible thumpers, who will justify their argument with biblical citations and take the Bible's own assertions as proof of its being true.

Formal definition[edit]

"given A (and whatever puffery is there to hide the fallacy), then (eventually) A".

Reduced to the statement "A implies A", this is actually the simplest form of tautology.

Legitimate uses[edit]

Technically speaking, every mathematical statement is a tautology. Tautologies can be useful for emphasizing important facts, or putting them in more useful forms. And naturally, any assumption that disagrees with a tautology is false.

See also[edit]

References[edit]

  1. E.g., see How Tautological Are Interspecies Correlations of Carcinogenic Potencies? by David A. Freedman et al. Risk Analysis vol. 13, no. 3, pp.265-272, 1993