Tu quoque (//, also //; Latin for, "you also") or the appeal to hypocrisy is an informal logical fallacy that intends to discredit the opponent's argument by asserting the opponent's failure to act consistently in accordance with its conclusion(s).
Tu quoque "argument" follows the pattern:
- Person A makes claim X.
- Person B asserts that A's actions or past claims are inconsistent with the truth of claim X.
- Therefore X is false.
An example would be
- Peter: "Based on the arguments I have presented, it is evident that it is morally wrong to use animals for food or clothing."
- Bill: "But you are wearing a leather jacket and you have a roast beef sandwich in your hand! How can you say that using animals for food and clothing is wrong?"
It is a fallacy because the moral character or past 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.
In the trial of Nazi 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 defense was rejected by the court, which convicted Barbie. 
- "tu quoque, n.". Oxford English Dictionary. Oxford University Press. 2012. Retrieved 24 April 2016.
- "Fallacy: Ad Hominem Tu Quoque". Nizkor project. Retrieved 24 November 2015.
- Bluedorn, Nathaniel (2002). The Fallacy Detective. p. 54. ISBN 0-9745315-0-2.
- "Logical Fallacy: Tu Quoque". Fallacyfiles.org. Retrieved 2014-06-17.
- Cohen, William "The Algerian War, the French State and Official Memory" pages 219-239 from Réflexions Historiques, Vol. 28, No. 2, Summer 2002 page 230.
|Look up tu quoque in Wiktionary, the free dictionary.|
- Agassi, Joseph (2008). "Rationality and the tu quoque argument". Inquiry. 16 (1–4): 395–406. doi:10.1080/00201747308601691.
- van Eemeren, Frans H.; Houtlosser, Peter (2003). "More about Fallacies as Derailments of Strategic Maneuvering: The Case of Tu Quoque". University of Windsor.
- Govier, Trudy (1980). "Worries About Tu Quoque as a Fallacy". Informal Logic. 3 (3): 2–4.
- Shapiro, Irving David (January 2011). "Fallacies of Logic: Argumentation Cons" (PDF). Etc. 64 (1): 75–86.
- Marcus, Kenneth L. (2012). "Accusation in a Mirror". Loyola University Chicago Law Journal. 43 (2): 357–93. SSRN .