Beware of the "Tu Quoque" Fallacy

"Tu Quoque" pronounced ("two coke" or even "two qwo qway" ) is a Latin phrase that means, "You, too." In conversations, it is often used as an attempt to dismiss or dismiss an opposing viewpoint because the person with the opposing viewpoint has acted inconsistently with that viewpoint.

"Tu Quoque" is a non-sequitur logical fallacy (meaning, "it does not follow") and, thus, is a thinking error. Semantically, the fallacy means, "If you don't follow your own rule perfectly, how can you expect others to follow it?"

Why is it a thinking error?

Just because a person makes an inconsistent assertion does not make that assertion false. It might indicate the person is hypocritical, but not that his assertion is false.

Unwarranted assumptions and ""Tu Quoque" errors are two of the most common (and, IMHO, the most egregious) thinking errors people make.

According to the Wikipedia, the form for the argument that commits this error is the following:

A makes criticism P.
A is also guilty of P.
Therefore, P is dismissed.

Teenagers sometimes use this argument in the following manner:

Mom: "Premarital sex is morally wrong. Don't do it."
Daughter: "Did you have premarital sex?"
Mom: "Yes."
Daughter: "Then who are you to tell me not to?"

The guilt, or innocence, of mom's past behavior is completely irrelevant to the issue of morality. If premarital sex is morally wrong, then it was morally wrong when mom did it and it will still be wrong if daughter does it.

Other examples to point out the absurdity of the error:

Jill: "I think the gun control bill shouldn't be supported because it won't be effective and will waste money."
Bill: "Well, just last month you supported the bill. So I guess you're wrong now."

"How can you tell me not to experiment with drugs when you did the same thing as a teenager?"

Beware of the "Tu Quoque" fallacy and refrain from committing it! Parents, PLEASE teaching your children critical thinking skills.  It's these skills that will help make them responsible adults,  and help lead them to Truth.