> You can find a list at literarydevices.net

Under ad hominem, this example is given:

   2. A classic example of ad hominem fallacy is
      given below:

   A: "All murderers are criminals, but a thief
       isn’t a murderer, and so can’t be a criminal."

   B: "Well, you’re a thief and a criminal, so there
       goes your argument."

OK, first of all, A's argument is terrible. He's asserting that all murderers are criminals, but to support the second half of his argument he really needs "all criminals are murderers". But the issue here is B's counterargument, so I'll let A get away with that.

How is this an ad hominem fallacy? B is not trying to discredit A's argument by appealing to a logically irrelevant characteristic of A. Rather, B is using A as a counterexample for A's argument. If instead B's argument was:

    B: "Well, C over there is a thief and criminal,
        so there goes your argument."

that would clearly not be an ad hominem. C provides an example of a person who is both a thief and criminal, which is a class of people that A claimed could not exist.

I see no logical reason that a person cannot serve as a refuting counterexample to a claim that they themselves made. If B had said:

    B: "Well, the jerk store called and they are
        running out of you, so there goes your
        argument."

that would be an ad hominem, because B is trying to get us to not believe A's argument because of the irrelevancy that the jerk store does a brisk business in A.

Another example to illustrate my point. Suppose A is a woman.

    A: "Women do not fart."

    (A then at once lets fly a fart as great as
     if it were a thunder-clap, and B is nearly
     blinded with the blast)

    B: "That's not true. You just farted!"

Would literarydevices.net claim that this is an ad hominem fallacy?

My take on this is that you are adding common sense, rather than sticking to what is given:

> How is this an ad hominem fallacy? B is not trying to discredit A's argument by appealing to a logically irrelevant characteristic of A. Rather, B is using A as a counterexample for A's argument.

But it's not a counterexample. It would be if someone had said thieves are criminals, but no one did. We only know that from common sense outside of the syllogism.

Therefore the statement "YOU are a thief and a criminal" is a simple assertion without evidence within the givens, and making such a statement about the debating opponent and then concluding they are therefore wrong ("there goes your argument") is in fact a solid example of ad hominem.

I strongly agree that this is a poor example of one, because it allows the sort of confusion that you point out -- it's just not literally wrong.

As a footnote (and certainly not aimed at you), a very large number of people who forgot their high school lectures about "ad hominem" use the term to mean any personal attack or criticism, which I find exasperating at best.

Such mis-usage isn't just language evolution in action, it is misunderstanding rhetorical concepts over 2000 years old, first stated in Greek and then Latin, and quite language independent.

It's a shame.

But I digress.

To interject, to me it seems that it is actually a counter-example, and I do not follow your reasoning. (A)'s argument is that murderers are criminals, but thieves are not murderers, and therefore cannot be criminals. The lack of logical validity of that argument aside, (B) refutes it instead by providing (quite literally) a counter-example: (A) is both a thief and a criminal. Therefore, if (B)'s assertion is true, (A)'s argument cannot be correct, for if it were correct, then (A) could be a thief or a criminal, but never both.

Since this is a logical argument, it prejudges the matter to conclude that the standard of evidence required for (B)'s assertion should be any different than that for (A)'s assertion. We know (A)'s assertion to be false without any extra information. If there were external details of evidence that could be introduced, then (A)'s assertion would still be false. (B)'s assertion, however, might then still be either true or false, depending on the extra lemmas. As the example does not make additional information necessary and does not mention additional information, it is an error to arrive at an interpretation in which additional information is required to make sense of the matter. (One can always arbitrarily arrive at such an interpretation.)