Tu quoque

Tu quoque (pronounced like 'too kwoh kway") (Latin for 'you also') is a form of ad hominem fallacy that occurs when it is assumed that an argument is wrong if the source making the claim has itself spoken or acted in a way inconsistent with it. The fallacy focuses on the perceived hypocrisy of the opponent rather than the merits of their argument. This is a fallacy regardless of whether you really did it or not, but it helps if you really didn't do it.

In short, just because someone doesn't practice what they preach, it doesn't mean what they preach is wrong.

Alternate names

 * Appeal to hypocrisy
 * Ad hominem tu quoque
 * You too!

Structure
The usual structure of the fallacy is:
 * 1) Person A makes claim X about Person B.
 * 2) Person B points out that claim X is also true of Person A.
 * 3) Therefore, X is irrelevant/false and A is a hypocrite.

This kind of reasoning is fallacious because criticism or objection to the person making the claim does not apply equally, if at all, to the argument itself. Certainly, if the premises are indeed true then source A is likely a hypocrite and should also be included in the guilty party, but this bears no relevance or relationship to the validity or factualness of the claim X. In essence, the claim X is being dismissed on grounds of a criticism of A, which is a non sequitur.

Examples


The response is only blaming the claimer for the same thing he/she did as well. This doesn't refute the fact Bob is a murderer, but only draws away the attention by involving another person.

In response to criticism
The first common variant of the fallacy is the "you criticize X, but you use something related to X" argument:

The fact that Alice is a smoker and drinker doesn't mean that she is wrong about the effects of those habits. Still confused? A better rebuttal would be to accept the premise that alcohol and smoking really are cancer risks, but then ask why Bob continues to do them. Perhaps Bob knows full well about the dangers of such addictions, but he may or may not be a hedonist with no sense of self-preservation, or it's just because he cannot or is yet to break from his very own addiction, hence why he continues to do it. Or because he is consciously or unconsciously suicidal, which makes his self-harm a logical consequence.

Another example is how (former) drug addicts who have suffered for their drug usage can also be very well qualified in admonishing others to not get started in harmful, expensive, illegal and addictive substances — sometimes due to personal experience and physical proof of the damage incurred by the drug addiction.

In response to support
The second common variant is "you support X, but you do not totally embrace X" argument, which is often doubly wrong:

This argument fails for two reasons: firstly, whether Alice moves to Canada does not affect the validity of the statement in any way; and secondly it is begging the question: Alice never actually said she liked Canada's health policies, just that they were more effective, and health care policies are not the only factor in choosing one's place of residence. For instance, Alice might be unwilling to leave her family behind regardless of the chance for better health care. Therefore not only is this argument a tu quoque, but also Alice's actions are not even inconsistent with her claims.

This specific claim, in which someone criticising a group is told to leave it if they do not like it, is sometimes called and often has jingoist implications.

With the law
A third common variation is "you're against X, but you just did X or had to do X to catch me doing X".

There is a very high chance someone who thinks this is a clever retort is either a freeman on the land/sovereign citizen or an extremely stupid ancap.

This is also a type of false dilemma since it implicitly assumes that all things regarded as crimes must necessarily be prosecuted equally: they are crimes for everyone or no one (this runs into certain problems when trying to define what "false imprisonment" is). The underlying argument is also a rather flawed attempt at an appeal to consequences ("If I'm guilty, so are you, so you should accept that I'm not because it is better for you that way"). Note that pointing to hypocrisy is not always a fallacy if it is used to attack the underlying reasoning of the law rather than simply to evade it: for example, if it is argued that violent movies are censored because people who watch them will become murderers, it is quite valid to ask why none of the censors themselves have become murderers.

False equivalency
One of the main problems with this fallacy is that it equates two separate actions, and it ignores all nuance that may make one of these actions okay and the other one not okay. In this example, H.P. Lovecraft has been dead for years, most of his work is in the public domain, and if we're talking about the Cthulhu Mythos as a whole there have been a great many authors besides Lovecraft who have had an influence on it. Thus, that action isn't directly equatable to giving money to a racist author who is still alive. One common example of this happening is when global warming denialists point out how climate activists use air conditioning, ride airplanes, etc. But this comparison is fallacious, as an individual's effect on the climate is very small, but the actions of large corporations and governments have a significantly larger impact on the environment, and it is completely fair for these activists to call out governments and corporations for not doing enough.

Presumption of hypocrisy
Similarly, this fallacy may make assumptions of double standards where they don't exist, and it tends to overlap with strawmanning and whataboutism in this way. In this example, Alice never said that she supported the Democrat's military budget, and she may support the Democrats for other reasons, but Bob assumes that because she was a Democrat, that means she must support everything that the Democrats have done. A proper response to the fallacy here would be to call out the assumptions that the opponent is making about your views without any evidence.

Thought-terminating cliché
When people use versions of the fallacy like this, they aren't even trying to make an argument; they're just telling their critics to shut up. Some cults like the Church of Scientology are notorious for doing this, often digging up all the dirt they can on their members so they can use it all against them if they ever start asking inconvenient questions. This fallacy just deflects from the critic's concerns and then puts the focus on them rather than on the issues they brought up.

Guilt by association
This fallacy is very frequently paired with the association fallacy (a.k.a., guilt by association), so that the person engaging in the fallacy need not even show that the other person's actions are inconsistent with their position; rather, it is merely shown that the actions of some other person somehow associated with that person did something inconsistent with that person's position. For instance, if someone criticizes Bill Clinton for his dishonesty, the common rejoinder is to bring up Bush's dishonesty. A similar case can be found when far-righters bring up Bill Clinton's dishonesty in response to any criticism of their 'God Emperor' Donald Trump. This is whataboutism.