Exposing PseudoAstronomy

November 17, 2009

Logical Fallacies: Ad hominem Follow-Up

Ad hominems and Assessing a Person’s Veracity

One thing I left out of my discussion of the ad hominem logical fallacy is that of assessing whether someone is actually being truthful or whether they may be trusted given their level of expertise with an issue.

While an ad hominem is still an ad hominem if it attacks a person rather than a claim, it can still speak towards the level of whether you should actually believe what someone claims.

For example, one of my secret pleasures is to watch Judge Judy court cases. Often during those cases, litigants – both defendants and plaintiffs – will try to bring up ad hominem attacks against their opponent in order to try to undermine the other’s case. Such as, “But he does drugs [so you shouldn’t trust him].”

While these are blatant ad hominems and the Judge often either ignores them or tells the person to just answer the question that was asked and to leave out commentary, sometimes very relevant ad hominems are allowed to stand and are explored. These are often of the circumstantial ad hominem variety. For example, if the plaintiff is suing for vandalism and brings up that the defendant has been prosecuted before for unrelated vandalism. While that does not provide any evidence as to whether the person did it this time, it does speak to the person’s character and a Judge can and often does consider that. Likewise, in federal and civil cases in “real” courts, cases will often hinge simply upon whether a jury believes one person or the other, and that is done based upon an analysis of their character as opposed to hard evidence about the actual circumstances.

Final Thoughts

While an ad hominem is still an ad hominem and does not speak at all to the actual claims or evidence that is presented, and hence it cannot be used to say whether or not that evidence is valid, they can be used and often are to asses whether the person’s claims actually should be looked at. Think of it as a “first pass:” If someone often lies about a topic, then they are unlikely to be believed about the next claim they make, regardless of whether that claim is true. For example, Rich Orman on the Dogma Free America podcast recently stated that Scientologists lie so often that if they said the sun rises in the east, he would start looking for it to come up in the west.


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