Ad Hominem Fallacy
A logical fallacy where an argument is rejected based on the character or circumstances of the person making it, rather than the argument itself. The fallacy occurs when attacking the person is irrelevant to the truth of their claims.
THE IDEA
Example 2:
An eyewitness is on the stand, testifying to the guilt of the accused. The defense attorney asks the eyewitness: “Isn’t it true that you’ve been convicted of perjury twice before, and, thus, you are a perjurer, a liar?”
Has the attorney committed an ad hominem fallacy? Let us consider our three critical questions. First, it would presumably be straightforward to assess whether the attorney’s allegations of perjury are true. If they aren’t, then his ad hominem argument is immediately beside the point (though it may still be damaging if not caught).
Second, note that the eyewitness, the proponent, is committed to two things: (1) to being in a position to know what happened, and (2) to speaking honestly about what happened. As a position to know argument, the support for the eyewitness’s claims comes from the claimed position to know. This is in contrast to an argument with explicit premises whose truth and relevance for the conclusion we could examine independently of the proponent’s character. Thus, the proponent’s character and credibility are highly relevant in regard to whether his testimony supports what he says. For if he is untrustworthy, we do not have good reason to trust what he says.
Third, what is the conclusion of the respondent’s argument? Is it that what the eyewitness says is false or that we should question it and not assent to it without further evidence from another source since the witness’s character is questionable? Well, being an untrustworthy liar does not mean that everything one says is false. At most, it means that one is not trustworthy and that others are fools if they uncritically accept what one says. Thus, if the respondent claims that the proponent’s testimony is false, then the respondent has argued fallaciously. However, if the respondent claims that the proponent’s testimony cannot be trusted, then we have been given reason to believe that is true given the truth of his being a perjurer. Thus, on this weaker reading, no fallacy has been committed. And since, in this example, it is a court case, the attorney need not attempt to show that the testimony is false; he merely needs to show that there is reason not to trust it.
When to use it
Evaluating arguments in political debates where opponents attack each other's character.
Assessing the credibility of expert testimony in a scientific or legal setting.
Identifying fallacious reasoning in online discussions and debates.
Teaching critical thinking skills to differentiate between valid and invalid personal attacks.
FROM THEORY TO EVERYDAY LIFE
In practice
Defense attorney attacking eyewitness credibility
A defense attorney questions an eyewitness who has two prior perjury convictions. The attorney suggests the witness is a liar. Whether this is fallacious depends on the intended conclusion: if aiming to prove the testimony false, it's fallacious; if aiming to show the testimony cannot be trusted, it is a legitimate challenge to credibility.
A MOMENT TO REFLECT
Put it to work.
How can you distinguish between a legitimate attack on a person's credibility and a fallacious ad hominem attack?
Think of a recent debate where someone's character was attacked. Was the attack relevant to the argument's validity?
When does a reason to doubt a witness’s honesty justify withholding belief, and why does it not prove the testimony false?
CONTINUE THE CONVERSATION
Source texts
- Bad Arguments 100 of the Most Important Fallacies in Western Philosophy (Steven Barbone, Michael Bruce)