Genetic fallacy

The genetic fallacy is a logical fallacy in which the origin of a belief, claim, or theory is confused with its justification. This fallacy is more often used to discredit a belief, though it may also be used to support one.

Examples:

• The Nazis were the first to practice eugenics. So it must be a bad idea.
• You only believe in God because your parents taught you to. So your belief must be false.

This is a fallacy because the origin of the claim has no logical relation to its truth or falsity.

However, if you were sure that the origin of the idea (a person, usually) was always correct or was always wrong, you could safely move from the origin of the claim to an evaluation of its truth or falsity. See Reliabilism and appeal to authority.

According to the Oxford Companion to Philosophy, the term originates in Morris Cohen and Ernest Nagel's book, Logic and Scientific Method.