- Person X presents an argument;
- There is something questionable about person X's character or circumstances; therefore
- Person X's argument should be rejected or avoided.
As with all informal fallacies, when it's used in a strong or deductive manner, ad Hominem is always fallacious; but when it's used informally or inductively, it may be pertinent.
The ad Hominem is classed as a fallacy of relevance; consequently, when it is encountered its relevance needs to be assessed as there may be instances where a person's character or circumstance does have a bearing on their claim.
Subtypes of ad Hominem
Abusive (Personal attack)
This is where the person's negative traits or characteristics (real or otherwise) are introduced in order to weaken or dismiss their argument. People may be called racist, fascist, homophobic, a TERF, etc. or likened to others who are perceived in this way. The idea is to show that the person making the claim cannot be trusted, has bad motives, is morally corrupt, or such an objectionable person that they should not be listened to.
The abusive ad Hominem is often used when people can't explain their position or defend it from counter-arguments in order to avoid debate. It's often simply a case of: Don’t like the message? Then shoot the messenger.
NOTE: An ad Hominem and an insult are not the same thing. An ad Hominem is used as a reason to reject or avoid the person's claim. An insult is simply abuse aimed at the person.
Poisoning the well
This is a pre-emptive personal attack. The person's character or circumstances are attacked before the person has had an opportunity to present their argument. The purpose of this is to bias people against the claimant in advance so they will not take the claimant seriously when they do encounter the claimant's argument.
As its name suggests, this version of ad Hominem appeals to a person's circumstances as being the motivation for why they're making the argument they are.
It is not necessarily abusive in nature, it's about raising doubts about the claimant's motivation for making their argument. e.g. a person's anti-abortion views could be rejected because they are a Catholic – the implication being that they're repeating religious dogma and not providing a reasoned argument.
People can indeed be influenced on matters by their circumstances, so this one can often be relevant.
Tu quoque, hypocrisy, inconsistency
This version of the ad Hominem focuses on inconsistencies in the claimant's position. Someone may make a claim that is inconsistent with how they act themselves or which contradicts something they've said before.
“You should give up smoking because it's bad for you” could be answered with “well you're a fine one to talk” if the person giving the advice is a smoker themselves. However, the advice is good whether the person giving the advice is a smoker or not – their indulgence in the habit doesn't weaken or negate their claim.
Evaluating ad Hominems
Any claim or information about a person that's introduced which is intended to affect their argument needs to be assessed. Although ad Hominems are always deductively fallacious, the information may be relevant. Look at this example:
“Teachers should be given a higher than inflation pay rise this year to reward the extra work they now have to do and to help retain good teachers.”
“You would say that. You're a teacher!”
This is a circumstantial ad Hominem. The fact that the person arguing for a teachers' pay rise happens to be a teacher doesn't invalidate their argument; however, there is also a possibility that this person's arguments are influenced by self-interest, so the information about the arguer's profession is relevant as it could affect the strength of their argument.
The main issues when assessing ad Hominem arguments are:
- Is the information introduced relevant; and if so
- To what extent?