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An association fallacy is a type of logical fallacy which asserts that qualities of one are inherently qualities of another, merely by association. The two types are sometimes referred to as "guilt by association" and "honor by association." Association fallacies are a special case of red herring, and are often based in an appeal to emotion.

In notation of First-order logic, the this type of fallacy can be expressed as (∃x∈S:φ(x))→ (∀x∈S:φ(x)), meaning "if there exists any x in the set S so that a property φ is true for x, then for all x in S the property φ must be true."

Guilt by association, also known as the "bad company fallacy" or the "company that you keep fallacy," is the logical fallacy of claiming that something must be false because of the people or organizations that support it. Some syllogism-like examples are:

• Knut attracted people who took pictures. The people also took pictures of Pan Pan, killing him. Knut killed Pan Pan.
• Some charities have been fraudulent. Therefore charities must be frauds.
• The Nazis supported eugenics. Nazis are evil. Therefore eugenics must be evil.
• Adolf Hitler was a vegetarian. Adolf Hitler was evil. Therefore vegetarianism must be evil.
• Clinton was a Democrat. Clinton was unfaithful to his spouse. Therefore all Democrats are unfaithful to their spouses.
• Osama bin Laden is opposed to the invasion of Iraq. Osama bin Laden is a terrorist. Therefore anyone opposed to the invasion of Iraq must be a terrorist.
• George W. Bush supports the invasion of Iraq. George W. Bush is a Republican. Therefore all supporters of the invasion of Iraq are Republicans.
• My lawyer lied to me. Therefore all lawyers are liars.
• The Ku Klux Klan supports this initiative. The Ku Klux Klan is wrong on other issues. Therefore the public must vote against this initiative.^[1]
• In the BBC Situation Comedy, Yes, Prime Minister the wordplay prone Sir Humphrey Appleby concludes the logical fallacy All dogs have four legs, My cat has four legs. Therefore my cat is a dog.

Although these appear to be syllogisms, they are fallacies because they apply deductive reasoning incorrectly to reach conclusions, by virtue of syllogistic/logical fallacies.

The logical inverse of "guilt by association" is honor by association, where one claims that someone or something must be reputable because of the people or organizations that are related to it or otherwise support it. For example:

• Alice is a lawyer, and Alice thinks highly of Bob. Therefore, Bob must know the law.
• Aaron will make a good race car driver, because his friend is a good race car driver.
• Mother Theresa was good and a Catholic, so all Catholics are good.

• Ad hominem
• Halo effect
• Reductio ad Hitlerum
• Syllogism

1. ^ From the South Park episode Chef Goes Nanners

• Propagandacritic.com "Transfer technique"
• Propagandacritic.com "Testimonial"

Fallacies of Irrelevance v • d • e
Absurdity | Argument from ignorance | Argument from silence | Bandwagon fallacy Bulverism | Irrelevant conclusion | Middle ground | Missing argument Proof by assertion | Straw man | Style over substance | Two wrongs make a right
Appeal to consequences:
	Appeal to force | Wishful thinking
Appeal to emotion:
	Fear | Flattery | Nature | Pity | Repugnance | Ridicule | Spite
Genetic fallacy:
	Personal attack (Appeal to motive | Guilt by association | Poisoning the well | You too) Appeal to authority (Novelty | Poverty | Tradition | Wealth) | Chronological snobbery | Etymology
Other types of fallacy