Tu quoque


Tū quoque, or the appeal to hypocrisy, is an informal fallacy that intends to discredit the opponent's argument by asserting the opponent's failure to act consistently in accordance with its conclusion. The Oxford English Dictionary cites John Cooke's 1614 stage play The Cittie Gallant as the earliest use of the term in the English language.

The fallacy

Tu quoque "argument" follows the pattern:
  1. Person A makes claim X.
  2. Person B asserts that A's actions or past claims are inconsistent with the truth of claim X.
  3. Therefore, X is false.
It is a fallacy because the moral character or actions of the opponent are generally irrelevant to the logic of the argument. It is often used as a red herring tactic and is a special case of the ad hominem fallacy, which is a category of fallacies in which a claim or argument is rejected on the basis of facts about the person presenting or supporting the claim or argument.

Example

In the trial of Nazi war criminal Klaus Barbie, the controversial lawyer Jacques Vergès tried to present what was defined as a Tu Quoque Defence—i.e., that during the Algerian War, French officers such as General Jacques Massu had committed war crimes similar to those with which Barbie was being charged, and therefore the French state had no moral right to try Barbie. This defence was rejected by the court, which convicted Barbie.