Abusive ad hominem
Explanation of the Abusive ad hominem
The most common and well-known version of the ad hominem fallacy is just a simple insult, and is called the abusive ad hominem. It occurs whenever a person has given up attempting to persuade a person or an audience about the reasonable of a position and is not resorting to mere personal attacks.
Examples and Discussion of Abusive ad hominems
Whenever you see personal attacks and abusive ad hominem arguments being used in a discussion, it is unlikely that anything productive will come out of it in the end. A person who can only make their case by attacking others probably doesn't have much of case to begin with.
1. Who cares what you think about movies? You're just an ignorant American who doesn't know anything about real culture.
2. You have claimed that John Edward doesn't really talk to the dead, but how can we believe what an atheist says?
In both cases, something objectionable is identified about a person: one is an ignorant American, the other is an atheist. The arguer then goes on to conclude that, just because of this objectionable fact, what they say about a particular topic should be ignored.
Instead of showing where the people have made an error in any of their statements, the argument simply attacks them for who they are and claims that we can dismiss anything said without even considering it. But in neither case is this objectionable fact related to the topic at hand — especially when these "objectionable" facts are just plain insults.
The proper way to evaluate the merits of an argument is by looking at what the argument says, not by distracting people's attention from the argument by insulting the person and then, unreasonably, concluding that your insult is a good reason to dismiss the argument.
Other common forms of the abusive ad hominem argument don't usually resort to clear personal insults:
3. John has been proven to be a liar numerous times, so I don't accept John's arguments about abortion.
4. Well, we shouldn't be surprised that Senator Smith supports this new tax - considering how long he has been living in Washington D.C. and working in politics, it would be a shock if he didn't support it!
With example #3, it may be true that the person has lied repeatedly in the past. Thus saying so is stating a matter of fact, not an insult. What's more, the fact that a person has lied in the past is, for most people, a reason to be skeptical of other things they say.
Nevertheless, it is not a logical reason to conclude that they never tell the truth again and it's not a sound basis for deciding that an argument of theirs is false. It may be a reason for questioning the accuracy or veracity of their premises, but not whether the conclusion follows from those premises. A person can be a pathological liar but still offer logically sound and valid arguments.
With example #4, there is no attempt to seriously criticize the new tax bill which is under consideration. Instead, there is just an attempt to subtly insult a Senator who supports it by attacking them for being in politics for so long. The implication here is that his character is questionable merely because of their political career.
In both of those examples, what is being criticized is the person, not what they are currently arguing. That's what makes them ad hominem fallacies.
Keep in mind that the following is not an abusive ad hominem:
5. John has been proven to be a liar numerous times, therefore you should reject his testimony and acquit my client.
Why does this differ from example #3 above? Because it is not an attempt to get you to reject John's argument. Instead, it's an attempt to get you to reject his testimony. A testimony is not an argument, it is a report of events. The fact that a person is a known liar has no bearing on whether or not a conclusion they are offering follows from the premises they are using. It does, however, affect how we evaluate their reporting of alleged facts.
Unfortunately, an abusive ad hominem can be very effective because it can divert people's attention away from the primary issue being debated. By making someone appear suspicious, ridiculous, or just inconsistent, people will start focusing on that rather than anything else. What's more, once people get suspicious of a person, it can be difficult for them to stop.
Finally, of course, it is possible to have an attack by itself:
6. You are just an ignorant twit.
This is an insult and it is abusive, but it is not an argument. Because it is not an argument, it cannot be a fallacy. Of course, that doesn't mean that such personal insults are OK — it's just that when they appear alone, they aren't logical fallacies.