An ad hominem argument, also known as argumentum ad hominem (Latin: "argument to the person" or "argument against the person") is an argument which links the validity of a premise to a characteristic or belief of a person advocating the premise. The ad hominem argument is not a fallacy despite there being fallacious instances of the argument.
Structure of the Argument
An ad hominem argument has the basic form:
- Person 1 makes claim X
- There is something objectionable about Person 1
- Therefore claim X is false
The first premise is called a 'factual claim' and is the pivot point of much debate. The contention is referred to as an 'inferential claim' and represents the reasoning process. There are two types of inferential claim, explicit and implicit. The fallacy does not represent a valid form of reasoning because even if you accept both co-premises, that does not guarantee the truthfulness of the contention. This can also be thought of as the argument having an un-stated co-premise.
In informal logic
In the past, the term ad hominem was sometimes used more literally, to describe an argument that was based on an individual, or to describe any personal attack. However, this is not how the meaning of the term is typically introduced in modern logic and rhetoric textbooks, and logicians and rhetoricians are in agreement that this use is incorrect.
- "You claim that this man is innocent, but you cannot be trusted since you are a criminal as well."
This argument would generally be accepted as reasonable, as regards personal evidence, on the premise that criminals are likely to lie to protect each other. On the other hand, it is a valid example of ad hominem if the source making the claim is doing so on the basis of evidence independent of its own credibility.
In general, ad hominem criticism of evidence cannot prove the negative of the proposition being claimed:
- "Paula says the umpire made the correct call, but this can't be true, because Paula is a woman."
Assuming Paula is a woman, her evidence is valueless, but the umpire may nonetheless have made the right call.
Types of ad hominems
Three traditionally identified varieties are ad hominem abusive (or ad personam), ad hominem circumstantial, and ad hominem tu quoque.
Ad hominem abusive
Ad hominem abusive (also called argumentum ad personam) usually and most notoriously involves insulting or belittling one's opponent, but can also involve pointing out factual but ostensible character flaws or actions which are irrelevant to the opponent's argument. This tactic is logically fallacious because insults and even true negative facts about the opponent's personal character have nothing to do with the logical merits of the opponent's arguments or assertions.
This tactic is frequently employed as a propaganda tool among politicians who are attempting to influence the voter base in their favor through an appeal to emotion rather than by logical means, especially when their own position is logically weaker than their opponent's.
- "You can't believe Jack when he says God exists. He doesn't even have a job."
- "Candidate Jane's proposal about zoning is ridiculous. She was caught cheating on her taxes in 2003."
Ad hominem circumstantial
Ad hominem circumstantial involves pointing out that someone is in circumstances such that he is disposed to take a particular position. Essentially, ad hominem circumstantial constitutes an attack on the bias of a source. The reason that this is fallacious in syllogistic logic is that pointing out that one's opponent is disposed to make a certain argument does not make the argument, from a logical point of view, any less credible; this overlaps with the genetic fallacy (an argument that a claim is incorrect due to its source).
On the other hand, where the source taking a position seeks to convince us by a claim of authority, or personal observation, observation of their circumstances may reduce the evidentiary weight of the claims, sometimes to zero.
- "Tobacco company representatives should not be believed when they say smoking doesn't seriously affect your health, because they're just defending their own multi-million-dollar financial interests."
- "He's physically addicted to nicotine. Of course he defends smoking!”
- "What do you know about politics? You're too young to vote!"
Mandy Rice-Davies's famous testimony during the Profumo Affair, "Well, he would [say that], wouldn't he?", is an example of a valid circumstantial argument. Her point was that since a man in a prominent position, accused of an affair with a callgirl, would deny the claim whether it was true or false, his denial, in itself, carries little evidential weight against the claim of an affair. Note, however, that this argument is valid only insofar as it devalues the denial; it does not bolster the original claim. To construe evidentiary invalidation of the denial as evidentiary validation of the original claim is fallacious (on several different bases, including that of argumentum ad hominem); however likely the man in question would be to deny an affair that did in fact happen, he could only be more likely to deny an affair that never did.
Ad hominem tu quoque
Ad hominem tu quoque (lit: "You too!") 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 fallacious because it does not disprove the argument; 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 on the negative consequences of the stated action.
- "You say that stealing is wrong, but you do it as well."
- "He says we shouldn't enslave people, yet he himself owns slaves."
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 A makes claim P.
- Group B also make claim P.
- Therefore, source A is a member of group B.
- "You say the gap between the rich and poor is unacceptable, but communists also say this, therefore you are a communist"
This fallacy can also take another form:
- Source A makes claim P.
- Group B make claims P and Q.
- Therefore, Source A makes claim Q.
- "You say the gap between the rich and poor is unacceptable, but communists also say this, and they believe in revolution. Thus, you believe in revolution."
A similar tactic may be employed to encourage someone to renounce an opinion, or force them to choose between renouncing an opinion or admitting membership in a group. For example:
- "You say the gap between the rich and poor is unacceptable. You don't really mean that, do you? Communists say the same thing. You're not a communist, are you?"
Guilt by association may be combined with ad hominem abusive. For example:
- "You say the gap between the rich and poor is unacceptable, but communists also say this, and therefore you are a communist. Communists are unlikeable, and therefore everything they say is false, and therefore everything you say is false."
A reductio ad Hitlerum argument can be seen as an example of a "guilt by association" fallacy, since it attacks a viewpoint simply because it was supposedly espoused by Adolf Hitler, as if it is impossible that such a man could have held any viewpoint that is correct.
Inverse ad hominem
An inverse ad hominem argument praises a source in order to add support for that source's argument or claim. A fallacious inverse ad hominem argument may go something like this:
- "That man was smartly-dressed and charming, so I'll accept his argument that I should vote for him"
As with regular ad hominem arguments, not all cases of inverse ad hominem are fallacious. Consider the following:
- "Elizabeth has never told a lie in her entire life, and she says she saw him take the bag. She must be telling the truth."
Here the arguer is not suggesting we accept Elizabeth's argument, but her testimony. Her being an honest person is relevant to the truth of the conclusion (that he took the bag), just as her having bad eyesight (a regular case of ad hominem) would give reason not to believe her. However, the last part of the argument is false even if the premise is true, since having never told a lie before does not mean she isn't now.
Appeal to authority is a type of inverse ad hominem argument.
- Hurley, Patrick (2000). A Concise Introduction to Logic, Seventh Edition. wadsworth, a division of Thompson Learning. pp. 125–128, 182. ISBN 0534520065.
- Copi, Irving M. and Cohen, Carl. Introduction to Logic (8th Ed.), p. 97-100.
- Walton, Douglas (1998). Ad Hominem Arguments. Tuscaloosa: University Alabama Press. pp. 240 pp.