An ad hominem (Latin for “to the man” or “to the person”), short for argumentum ad hominem, means responding to arguments by attacking a person’s character, rather than addressing the content of their arguments. When used inappropriately, it is a fallacy in which a claim or argument is dismissed on the basis of some irrelevant fact or supposition about the author or the person being criticized. Ad hominem reasoning is not always fallacious, for example, when it relates to the credibility of statements of fact or when used in certain kinds of moral and practical reasoning.
Fallacious ad hominem reasoning is normally categorized as an informal fallacy, more precisely as a genetic fallacy, a subcategory of fallacies of irrelevance.
Abusive ad hominem usually involves attacking the traits of an opponent as a means to invalidate their arguments. Equating someone’s character with the soundness of their argument is a logical fallacy.
Ad hominem abuse is not to be confused with slander or libel, which employ falsehoods and are not necessarily leveled to undermine otherwise sound stands with character attacks.
Ad hominem tu quoque (literally: “You also”) refers to a claim that the source making the argument has spoken or acted in a way inconsistent with the argument. In particular, if Source A criticizes the actions of Source B, a tu quoque response is that Source A has acted in the same way. This argument is false because it does not disprove the premise; if the premise is true then Source A may be a hypocrite, but this does not make the statement less credible from a logical perspective. Indeed, Source A may be in a position to provide personal testimony to support the argument.
For example, a father may tell his son not to start smoking as he will regret it when he is older, and the son may point out that his father is or was a smoker. This does not alter the fact that his son may regret smoking when he is older.
Ad hominem circumstantial points out that someone is in circumstances such that they are disposed to take a particular position. Ad hominem circumstantial constitutes an attack on the bias of a source. This is fallacious because a disposition to make a certain argument does not make the argument false; this overlaps with the genetic fallacy (an argument that a claim is incorrect due to its source).
The circumstantial fallacy applies only where the source taking a position is only making a logical argument from premises that are generally accepted. Where the source seeks to convince an audience of the truth of a premise by a claim of authority or by personal observation, observation of their circumstances may reduce the evidentiary weight of the claims, sometimes to zero.
Guilt by association
Guilt by association can sometimes also be a type of ad hominem fallacy if the argument attacks a source because of the similarity between the views of someone making an argument and other proponents of the argument.
This form of the argument is as follows:
- Source S makes claim C.
- Group G, which is currently viewed negatively by the recipient, also makes claim C.
- Therefore, source S is viewed by the recipient of the claim as associated to the group G and inherits how negatively viewed it is.
An example of this fallacy could be “My opponent for office just received an endorsement from the Puppy Haters Association. Is that the sort of person you would want to vote for?”