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.

Example:
"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.

Example:
"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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