The Tu Quoque Fallacy

The tu quoque fallacy occurs when someone accused of something, trying to deflect away the criticism, accuses his or her opponent of the same thing in an attempt to defend the error.  Here's a scenario.  A thief breaks into the house of her neighbor.  When caught and condemned by the neighbor, she brings to his attention that he has stolen from her in the past and that therefore her actions are justifiable.  The two point their fingers at each other.

Consider another example.  A man uses a logical fallacy in an argument, and his opponent mentions this.  But the man, remembering that his opponent used a logical fallacy just earlier in the conversation, cries out about the earlier fallacy of the other person.  Both individuals have used a logical fallacy.  The former says that his fellow's use of a fallacy means that his should be overlooked.

Is drawing attention to hypocrisy in situations like these logically fallacious?  Not in itself.  The way that hypocrisy is pointed out and the intent in doing so determine whether someone is committing the tu quoque fallacy or just observing an inconsistency--the two are objectively distinct.  Noting and mentioning that a person has committed the very fault he or she is criticizing is legitimate, as long as one does not use this as some sort of justification or defense for his or her own error.

There is a difference between pointing out hypocrisy and acting like pointing out hypocrisy absolves you of your own faults, and this is an important thing to clarify.  Not everyone who identifies a mistake he or she has committed in the actions or words of another person is being fallacious, but doing so does not make past mistakes right, as it only correctly points out that another person has done the same.  The tu quoque might seem, especially in certain contexts (like a political debate), like a tempting way to make oneself appear justified by making an opponent look morally or intellectually inconsistent, but the hypocrisy of an opponent does not nullify any legitimate criticism that the opponent brings against another.