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The fallacy fallacy, or argumentum ad logicam, is the informal (and rather counter-intuitive) logical fallacy that if an argument contains a logical fallacy, the entire proposition is wrong. This is where one needs to make a clear distinction between "sound", "valid" (including the distinction between scientific validity and logical validity) and "true", instead of taking all of them as synonymous.  It takes the following form:
- Argument A supports the proposition P
- Argument A contains a logical fallacy.
- Therefore, the entirety of P is false
There is nothing wrong with pointing out that the argument A is invalid. However, claiming that the entirety of proposition P (which could otherwise be an objective scientific truth or is supported by better arguments) is false, just because it could be, or is being, supported by fallacious argument A, is the Fallacy fallacy.
This is a special case of denying the antecedent.
 Correct usage
An argument of that form is perfectly valid when all possible arguments for a proposition are fallacious - indeed showing that all propositions are fallacies or somehow wrong is the way to disprove something, barring the proposition being unprovable, of course.
Fallacies of distraction or relevance (e.g. Straw man, Red herring) are something of a special case; if one of these fallacies is demonstrably present, the conclusion is not necessarily wrong, but it is, by definition, irrelevant.
However, due to the likely large number of arguments and fallacious arguments (from someone attempting a Gish gallop, for instance) in support of a proposition P, it would be easier to prove not P than to go about countering the various fallacious arguments, although this can be difficult when one's opponent is just asking questions and otherwise spewing bullshit, not even directly claiming that P is true.
This fallacy's use is staggeringly common during internet debates, where pseudo-intellectualism reigns supreme. A person will seek out and attack any logical fallacy you use and dismiss your argument out of hand, without ever addressing the proposition. Fairly often, you might spot someone who will not even bother explaining why the fallacy is appropriate in that context. Some of the possible causes of this phenomena include: they are being lazy and are just arguing by assertion, they are trying to distract from their argument and are poisoning the well, or they learnt a fancy new Latin phrase and want to use it regardless of its applicability. If they have incorrectly used the fallacy then they have committed the fallacy fallacy fallacy.
 Fallacy fallacy fallacy
Like Cohen's Law, this stacks nicely, or with bemusing confusion. For a start, since the fallacy fallacy is itself a fallacy, it cannot be used to label an argument's conclusion as false without committing it in the process. "You have used the fallacy fallacy, therefore you are wrong" is a much an example as "you have used an ad hominem, therefore you are wrong" would be. In addition:
- A fallacy is an argument that doesn't follow proper rules of logic.
- A fallacy fallacy happens because true statements can be defended through fallacious arguments. Merely proving that an argument is fallacious does not prove that the whole entire position that it defends is immediately false.
- A fallacy fallacy fallacy then, is the claim that disproving particular arguments or versions of a position is irrelevant to disproving the position itself. While fallacious reasoning in support of a position does not, in itself, provide absolute proof that the position is false, it does mean that the person making the argument has failed to present any case for it to be true.
Assertions that are supported only by fallacious reasoning and special pleading to get around debunked arguments, are unlikely to have much truth value. An example where this is very common is among psychics. Numerous individual psychics have been proven to be frauds, and study after study has shown particular psychic abilities to not exist. Yet still there is an inexhaustible supply of psychics and alleged psychic abilities - and people who can pay their wares. Hence, if any of this mountain of evidence against psychic powers is cited, psychics can merely reply "Well, you haven't proven me to be a fraud."
 Fallacy fallacy fallacy fallacy
A fallacy fallacy fallacy fallacy describes the improper application of a fallacy fallacy fallacy. Additionally, a fallacy fallacy fallacy fallacy may be misrepresented, resulting in a fallacy fallacy fallacy fallacy fallacy... ad infinitum.
The following argument displays the fallacy fallacy:
- The argument from design supports the proposition "God exists."
- The argument from design is fallacious.
- Therefore, God does not exist.
Although the premises do provide strong evidence against a God as an interfering designer, these alone do not arrive at the more general conclusion of "God does not exist".
 See also
- The Adventures of Fallacy Man, Existential Comics