Ad Hominem Tu Quoque
Ad Hominem Tu Quoque, often shortened to Tu Quoque, is one of the most socially accepted, and even socially encouraged, fallacies in regular use today. In modern English it might best be phrased 'the hypocrisy fallacy', as it is based on a misunderstanding of the nature of hypocrisy. It goes like this:
1. You said P.
2. You either said, or indicated through your actions, that not P.
3. Therefore, I get to choose whether P or Not-P is true, regardless of any further information.
The specific fallacy occurs in assuming that truth comes from the person speaking, as long as the person speaking is consistent. This is contrary to the normal assumption, that truth exists as an external fact. If someone falls for the Tu Quoque fallacy, this suggests that they are more interested in 'winning' an argument than in finding the truth.
1. You say that God exists.
2. You say that we must follow the the word of God.
3. You say that the Bible is the word of God.
4. You eat pork, in contradiction to the Bible.
5. Therefore, I can choose that God does not exist.
It should be obvious that if God does exist, this argument would not keep you out of hell. However, this chain of logic does produce a useful result. It would be appropriate to conclude either:
5. You are not a reliable source of information.
5. I must choose which of your explicit or suggested statements to disregard.
If you find yourself making the Tu Quoque fallacy, this indicates that you are not truly interested in the conversation as a means of educating yourself in the true nature of the universe, and is a strong indicator that you are either a troll or are being sucked in by a troll. The correct thing to do is either leave the argument immediately, or start using more antagonistic language and make frequent references to Hitler.
Ad Hominem Tu Quoque is pronounced 'ad ho-mih-nem too kwoh-kwee' (IPA, /tuːˈkwoʊkwiː/). It is Latin for 'you also, to the man', or more roughly, 'you are basing your argument on the assumption that you are better than you are'.