Friday, May 28, 2010

Fallacy: Tu Quoque

This fallacy is committed when it is concluded that a person’s claim is false because it is inconsistent with something the person has said or done.

You-too version:
A makes criticism P
A is also guilty of P
Therefore, P is dismissed

The fact that a person's claims are not consistent with his actions might indicate that the person is a hypocrite but this does not prove his claims are false.

"He cannot accuse me of libel because he was just successfully sued for libel."

Inconsistence Version:
Person A makes claim X
Person B asserts that A's past claims are inconsistent with the truth of claim X
Therefore X is false

This is a logical fallacy because the conclusion that P is false does not follow from the premises; even if A has made past claims which are inconsistent with P, it does not necessarily prove that P is either true or false.

"You say aircraft are able to fly because of the laws of physics, but this is false because twenty years ago you also said aircraft fly because of magic."


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