So’s Your Old Man: Adventures in Logic II

Dear Children:

In the study of logic, there is a fallacy called argumentum ad hominem (against the person). Of course it is often a personal attack but more often it is an attack made against an adversary’s associations, lifestyle, education and parentage. It is a fallacy because such an attack does not speak to the validity of a proposition. Girls aren’t supposed to know anything about math or science. Short people don’t know basketball. Plain people should not be giving fashion tips. Beware of Greeks bearing gifts. You get the idea.

There are many specific brands of the ad hominem fallacy such as Circumstantial when a claim is made by someone who has special or secret knowledge. When someone says they have secret knowledge, that claim may be true or false but the speaker’s credibility is nonexistent.

A proposition may be attacked when the source appears to have a Conflict of Interest. For a source to be authoritative it must be both objective and impartial. The evidentiary weight of an argument diminishes with the benefit that accrues to the source.

Guilt by association is also a fallacy in this category. There is no bearing on the validity of a statement concerning crime from the mouth of a criminal.

But, it’s another special kind of ad hominem fallacy we see around us the most. It is called Tu Quoque; literally “you too”. This, finally, is a subject dear to the hearts of us all; hypocrisy.

We are highly sensitive when it comes to hypocrisy. “Do what I say, not what I do.” We don’t listen to those who fail to practice what they preach. We know for sure that “If you lie down with dogs, you get up with fleas” attributed to Benjamin Franklin’s Poor Richard’s Almanac. In modern political parlance, we call such people flip-floppers or worse. You are sensible to be suspicious of such people. Unfortunately, your suspicion does not amount to a refutation of their claim.

Please understand that it must be this way. No less a figure than Jesus has asked us to examine our hearts to see if we are righteous enough to cast the first stone (John 8:7). In logic, too, the sins of a speaker do not say a true thing about the speaker’s words.

If a speaker is wrong, we’ll just have to prove it another way.

I’m just sayin’

Poppy