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Genetic Fallacy

October 8th, 2009

Taxonomy – Where am I?

Genetic Fallacy

classification : informal – red herring

To argue that a claim is true or false on the basis of its origin. Genetic accounts of an issue may be true, and they may help illuminate the reasons why the issue has assumed its present form, but they are irrelevant to its merits.


There is a difference between a reason why something is believed (ratio credentis, an explanation) and a reason why something is true (ratio veritatis, a justification). Ideally the latter would be used for the former, but we do often have reasons, even good reasons, for believing things even if we do not know the reasons why they are true. But if reasons for belief are used as though they are reasons for truth, this has been recognized for most of the history of logic as an informal fallacy, the “genetic fallacy,” in which the origin or the cause of a proposition is taken to have some bearing on its truth. It doesn’t. The fallacy can take two common forms that are of interest: an ad hominem (“against the man”) argument holds something to be false because of where it comes from; and an argument “from authority” (ab auctoritate) holds something to be true because of where it comes from. Both ad hominem arguments and arguments from authority can be very good reasons to believe, or not to believe, something, but they are not logical reasons why something is true. An argument relevant to the truth of its proper subject matter may be called an argumentum ad rem (“concerning the thing,” or “to the point”).


Sure, the media claims that Senator Bigwig was taking kickbacks. But we all know about the media’s credibility, don’t we.

The idea that there are measurable IQ differences among different races is the sort of thing that racists believe and argue for.

Sub Fallacies

Ad Hominem
Appeal to Misleading Authority
Etymological Fallacy

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Categories: Logic