argumentum ad logicam
(also known as: disproof by fallacy, argument to logic, fallacy fallacy, or fallacist's fallacy, bad reasons fallacy [form of])
Description: Concluding that the truth value of an argument is false based on the fact that the argument contains a fallacy.
Argument X is fallacious.
Therefore, the conclusion or truth claim of argument X is false.
Ivan: You cannot borrow my car because it turns back into a pumpkin at midnight.
Sidney: If you really think that, you’re an idiot.
Ivan: That is an ad hominem; therefore, I can’t be an idiot.
Sidney: I beg to differ.
Explanation: While it is true that Sidney has committed the ad hominem fallacy by calling Ivan an idiot rather than providing reasons why Ivan’s car won’t turn into a pumpkin at midnight, that fallacy is not evidence against the claim.
Karen: I am sorry, but if you think man used to ride dinosaurs, then you are obviously not very well educated.
Kent: First of all, I hold a PhD in creation science, so I am well-educated. Second of all, your ad hominem attack shows that you are wrong, and man did use to ride dinosaurs.
Karen: Getting your PhD in a couple of months, from a “college” in a trailer park, is not being well-educated. My fallacy in no way is evidence for man riding on dinosaurs, and despite what you may think, the Flintstone’s was not a documentary!
Explanation: Karen’s ad hominem fallacy in her initial statement has nothing to do with the truth value of the argument that man used to ride dinosaurs.
Exception: At times, fallacies are used by those who can’t find a better way to support the truth claims of their argument -- it could be a sign of desperation. This can be evidence for them not being able to defend their claim, but not against the claim itself.
Variation: The bad reasons fallacy is similar, but the argument does not have to contain a fallacy -- it could just be a bad argument with bad evidence or reasons. Bad arguments do not automatically mean that the conclusion is false; there can be much better arguments and reasons that support the truth of the conclusion.
I have never seen God; therefore, he does not exist.
This is a terrible reason to support a very strong conclusion, but this doesn’t mean that God does exist; it simply means the argument is weak.