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The genetic fallacy creates a fallacious argument that is accepted or rejected based on the source of the evidence, rather than on the quality or applicability of the evidence. It is also a line of reasoning in which a perceived defect in the origin of a claim or thing is taken to be evidence that discredits the claim or thing itself. The fallacy is committed when an idea is either accepted or rejected because of its source, rather than its merit.
The genetic fallacy is a logical fallacy but is frequently not a Bayesian one: some sources are so consistently full of it that they reasonably constitute a refutation for all practical purposes. However, that this is a logical fallacy means you will still need to convince the source's fans and bystanders by engaging the source material.
- Socrates says that he is mortal.
- Socrates is a pagan - only Christians are trustworthy.
- Therefore Socrates is immortal.
Note that there are cases where this type of argument may not be fallacious. For example, there are some cases in which the origin of a claim is relevant to the truth or falsity of the claim, such as a claim that comes from a reliable expert is likely to be true (provided it is in her area of expertise).
- "The current Chancellor of Germany was in the Hitler Youth at age 13. With that sort of background, his so called 'reform' plan must be a fascist program."
- "I was brought up to believe in a god, my parents told me a god exists, and my parents would never lie to me, so this god must exist."
- "Sure, the media claims that Senator Wales was reading pornography. But we all know about the media's credibility, don't we."
The genetic fallacy is an umbrella term for a number of fallacious arguments trying to misdirect the line of reasoning by invoking the origins of a claim. For example:
- Argumentum ad hominem ("The source is an idiot, therefore their claim is wrong.")
- Argument from (misleading) authority ("The source is a genius, therefore their claim is right.")
- The etymological fallacy: mistaking the origins of a word for its "real" or "true" meaning
- Reductio ad Hitlerum ("Hitler ate sugar, therefore sugar is bad.")
- The Genetic Fallacy, entry in the Fallacy Files