This fallacy strikes when a speaker or writer lobs a personal insult or otherwise launches a personal attack upon another in an attempt to undermine that person's argument. In other words, instead of countering another's argument by showing its faults, the arguer attacks the person—by calling him a name, attributing an undesirable quality to him, assigning him responsibility for an objectionable event or action. It doesn't matter whether the attack contains true or false information; if that information has no bearing on the argument, claim, or position, the arguer has inserted an ad hominem fallacy.

These examples illustrate what is called the "abusive" ad hominem fallacy, each directed toward a person rather than an argument:

• "We need to reject Ms. Colby's latest initiative; her last one failed miserably."
• "That chinless wonder couldn't even coach a team of third-grade girls."
• "I'm opposed to anything that idiot Handel supports."

Several types of the ad hominem fallacy grow from the same festering soil in which the abusive one so profusely blooms. Each type ignores an argument or position and instead focuses on the person presenting it. The big three:

• The "circumstantial" ad hominem suggests that a person is taking a particular position because his circumstances predispose him to do so; it implies that he's advocating that position only to advance his own self-interest. Suppose a town council proposes building a parking garage; a constituent maintains that the council members will profit from that construction because they all own businesses near the selected location. That constituent has committed the circumstantial ad hominem fallacy. He needs first to focus on the proposal, its claims and support, and show them to be inadequate.


• The tu quoque ("you're another") fallacy occurs when a person is attacked for not following the advice she gives. If a CFO argues for improving the company's solvency ratio, for example, an opponent might use the tu quoque fallacy by accusing the CFO of not keeping her own finances in order. Yet the state of her personal finances is not relevant to the argument she makes regarding the company's solvency ratio.


• "Poisoning the well" refers to the practice of attempting to discredit an opponent—or his argument—before one or both is even presented. Preemptively saying that a person is known for the dramatic price increases his company has instituted in the past year poisons the well. So does handing an article to a colleague while warning, "Before you read this, I should point out that analogy is the weakest of arguments."

In logic, the pertinent question is not who makes the argument but whether the argument is valid. You cannot refute an argument or claim by attacking an opponent's character, motives, or traits. Instead, you must attack the argument—show where its reasoning droops, its support distorts, its facts fail.

While all logical fallacies render an argument unsound, the argumentum ad hominem carries the extra baggage of incivility. Perhaps there's already enough of that. Perhaps, too, there's enough deception, even if you could fool all the people some of the time and some of the people all the time. Sharpening your awareness of ad hominem fallacies can help you cut both down to size … in one fell swoop.