Tu quoque (/ /,; Latin Tū quoque, for "you also"), or the appeal to hypocrisy, is an informal fallacy that intends to discredit the opponent's argument by attacking the opponent's own personal behavior as being inconsistent with the argument's conclusion(s). This specious reasoning is a special type of ad hominem attack. It is used frequently with "whataboutism" being one particularly well known instance of this fallacy. 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 (fallacious) tu quoque argument follows the template (i.e. pattern):
As a specific example, consider the following scenario where Person A and Person B just left a store.
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.
The example above was worded in a way to make it amenable to the template given above. However, in colloquial language, the tu quoque fallacy more often makes an appearance in more subtle and less explicit ways, such as in the following example in which Person B is driving a car with Person A as a passenger:
Although neither Person A nor Person B explicitly state what X is, because of the colloquial nature of the conversation, it is nevertheless understood that statement X is something like: "Running stop signs is wrong" or some other statement that is similar in spirit.
Person A and/or Person B are also allowed to be groups of individuals (e.g. organizations, such as corporations, governments, or political parties) rather than individual people.[note 1] For example, Persons A and B might be governments such as those of the United States and the former Soviet Union, which is the situation that led to the term "whataboutism."
The tu quoque fallacy can also appear outside of conversations. For example, it is possible for someone who supports a certain Politician B, who recently did something wrong, to justify not changing their support to another politician by reasoning with themselves:
In this example, Person B was "Politician B" while Person A was "other politicians."
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.