Ad Hominem Fallacy

The ad hominem argument (Latin for "to the man") is an attempt to counter another's argument by making an irrelevant attack on the arguer rather than the argument itself. As such, there are two elements of a fallacious ad hominem: (1) the critic responds to an argument with a personal attack on the arguer, ignoring the argument itself. (2) The personal attack on the arguer is irrelevant to any assessment of the argument.

The fallacy generally takes on the following form:

1. Person A makes claim X.
2. Person B attacks person A
3. Therefore A's claim is false or should be disregarded.

Types of ad hominems
Ad hominem's are commonly divided into various categories, two of which are the abusive and circumstantial.

The abusive/direct ad hominem is a direct attack which irrelevantly questions or vilifies the arguer's character. It is argued that because the person's character is in someway defective, what they claim must be incorrect or unreasonable. This is generally thought of as being fallacious in that the character of a person does not (usually) have a bearing on the truth or falsity of the claim being made.

Examples of abusive ad hominem:

"That claim cannot be true. Dave believes it, and we know how morally repulsive he is."

Tom says "I think we should stop affirmative action because it creates inequalities." Mike replies "You need to stop being so racist."

The circumstantial ad hominem attempts to refute the arguer's claim by questioning or criticizing their personal circumstance. It asserts the personal situation or circumstance as the reason the arguer puts forth their argument and as such the argument should be discarded. Typically this is done by attacking the arguer by asserting that they are simply making their claim for self-interested reasons. The fallacy with this line of thinking is that though the personal circumstances of the arguer may explain their motives, it does not affect the truth or falsity of the claim being made.

Examples of ad hominem circumstantial:

"Of course the Senator from Maine opposes a reduction in naval spending. After all, Bath Ironworks, which produces warships, is in Maine"

“I think that we should reject what Father Jones has to say about the ethical issues of abortion because he is a Catholic priest. After all, Father Jones is required to hold such views.”

Other forms of the ad hominem fallacy include Poisoning the Well, Tu Quoque and Guilt By Association.

Legitimate Attacks on the Person
Due to the standard presentation of the ad hominem as being an informal fallacy, it can easily be mistaken to be a consistent error in reasoning. But the key question to ask before dismissing an ad hominem is whether the attack is relevant to the point being argued.

The classic example of it's legitimate use is when a cross-examining lawyer attacks the trustworthiness of a witness in order to cast doubt upon their testimony. In this instance, it would not be improper for the lawyer to point to a pattern of untrustworthy behavior on the part of the witness as it is directly relevant to the credibility of their testimony.



Logical Self-defense, Johnson & Blair
Fallacy Files: Ad Hominem
The Nizkor Project: Ad Hominem
The Nizkor Project: Circumstantial Ad Hominem
Informal Logical Fallacies: A Brief Guide
Scientific America: Character Attacks: How to Properly Apply the Ad Hominem
Formalization of the ad hominem argument scheme