Three Major Forms:

1. ad hominem abusive: instead of attacking an assertion, attacking the person who made the assertion.
2. ad hominem circumstantial: instead of attacking an assertion, the author/speaker points to the interrelationship between the assertion and the person's circumstances.
3. ad hominem tu quoque: attacking a person for not “practicing what he/she preaches.”

Examples:

1. You argue that God doesn't exist, but you are just following a fad. (abusive)
2. We should discount what Premier Klein says about taxation, because he won't be hurt by the increase. (circumstantial)
3. We should disregard Share B.C.'s argument, because they are being funded by the logging industry. (circumstantial)
4. You say I shouldn't drink, but you haven't been sober for more than a year. (tu quoque)

Convincing Others: Identify the argument(s) that are attacking the character of or circumstances surrounding the person and show that they have nothing to do with the truth or falsity of the proposition being defended.

References: Barker: 166; Cedarblom and Paulsen: 155; Copi and Cohen: 97; Davis: 80

1. the person is not qualified to have an expert opinion on the subject,
2. experts in the field disagree on the issue,
3. the authority was making a joke, drunk, or otherwise not being serious at the time when the cited statement was made.

Examples:

1. Noted psychologist Dr. Frasier Crane recommends that you buy the EZ-Rest Hot Tub.
2. Economist John Kenneth Galbraith argues that a tight money policy is the best cure for a recession. (Although Galbraith is an expert, not all economists agree on this point.)
3. We were headed for nuclear war. President Ronald Reagan remarked that we begin bombing Russia in five minutes. (Of course, he said it as a joke during a microphone test.)
4. My friend heard on the news the other day that Canada will declare war on Serbia. (This is a case of hearsay; in fact, the reporter said that Canada would not declare war.)
5. The Ottawa Citizen reported that sales were up 5.9 percent this year. (This is hearsay; we are not in a position to check the Citizen's sources.)

Convincing Others: Show that either

1. the person cited is not an authority in the field or
2. there is general disagreement among the experts in the field on this point.

References: Cedarblom and Paulsen: 155; Copi and Cohen: 95; Davis: 69

A variation on this fallacy is the "appeal to rumor." Because the source of a rumor is typically unknown, we cannot usually determine its reliability.

Examples:

1. A government official said today that the new gun law will be proposed tomorrow.
2. Experts agree that the best way to prevent nuclear war is to prepare for it.
3. It is held that there are more than two million needless operations conducted every year.
4. Rumor has it that the Prime Minster will declare another holiday in October.

Convincing Others: Argue that because we don't know the source of the information we have no way to evaluate its reliability.

Reference: Davis: 73

Examples:

1. Nixon lost the presidential debate because of the sweat on his forehead.
2. Trudeau knows how to move a crowd. He must be right.
3. Why don't you take the advice of that nicely dressed young man?

Convincing Others: While it is true that an argument's presentation may affect its acceptability, the truth or falsity in its conclusion does not depend upon the style of presentation. Just show that the argument's presentation has no relevance to the truth or falsity in the conclusion.

Reference: Davis: 61