Argumentum ad hominem

You reject what someone has said by pointing at the person who said it. The argument works on the assumption that who makes a claim settles whether it is true, so the speaker’s character, situation or conduct is offered as reason enough to dismiss the claim without examining it. It can be attacked by observing that a claim can be correct whoever happens to make it.

Example

Your claim that everyone should become a vegetarian makes no sense. You work at a seafood restaurant!

Standardised form

“Everyone should become a vegetarian” (q) is unacceptable (U) because “everyone should become a vegetarian” (q) is said by you (Z).

Transformations applied: “because” inserted between the two sentences; “your claim that everyone should become a vegetarian” resolved into the quoted proposition; the claim’s unacceptability made explicit as the conclusion-predicate; the second sentence set aside as support for the lever, see the Notes below.

Classification

The conclusion is referred to as a whole in the premise, so the argument form is delta (q is U because q is Z).

The premise attributes the conclusion to the addressee, so the argument substance is II.

The keyword CHARACTERALLY AUTHORITATIVE describes the relationship between predicates Z and U. The argument lever can thus be formulated as “Being said by you (Z) is CHARACTERALLY AUTHORITATIVE for being unacceptable (U)”.

Not to be confused with

• Ethotic argument — The premise points at the arguer themselves, and supports acceptability. I, A
• Argumentum ad baculum — Also addressed to the second person, but the premise offers a threatened harm rather than a bad character. NEGATIVE MOTIVATION
• Argumentum ad carotam — Also addressed to the second person, but the premise offers a promised benefit. OFFERED REWARD
• Argument from expert opinion — A third party, and acceptability supported rather than attacked. III, A

Source

Invented example.

Notes

The second sentence of the example expresses the fact that the source of the claim works in a seafood restaurant, and can be reconstructed as a premise that supports the lever of the original argument: “Being said by you is CHARACTERALLY AUTHORITATIVE for being unacceptable because you work at a seafood restaurant.”

The tradition distinguishes three variants: (1) the direct or abusive ad hominem, which attributes a negative characteristic to the source; (2) the indirect or circumstantial ad hominem, which doubts the source’s motives for endorsing the claim; and (3) the tu quoque, which points out an inconsistency between the source’s behaviour and their believing the claim.

While the tradition reserves the label ad hominem for attacks on the other party in the discussion, and thus for the second-person perspective, there is no reason it could not also be used for arguments in which the unacceptability of a claim is supported by attacking a third party. In that case the argumentum ad hominem has substance III and can be interpreted as a negative argument from authority.