Tag Archives: Fallacies

Ad Populum Mitosis?

While studying informal fallacies to prepare the next lesson in my upcoming rhetoric text Fitting Words, I observed something surprising about the ad populum fallacy. I have generally understood this fallacy to be simply an appeal to the masses, indeed to the mere mass of the masses” (Introductory Logic, Nance and Wilson) as in “Mom, all my friends are doing it!” (for which all mothers have learned the counterexample “If all your friends were jumping off of a cliff, should you?”)

But in all the standard college logic texts that I own (not a small sample), argumentum ad populum is taken to mean, quite broadly, an improper appeal to emotion. As a sample: Continue reading Ad Populum Mitosis?

Watch your assumptions!

In his Institutes of Oratory, the rhetorician Quintilian, in discussing the value of learning logic, mentions the “horn” problem, which evidently was this tricky syllogism:

“You have what you have not lost. You have not lost horns. Therefore you have horns.”

Initially I supposed that this was invalid, until I put it into categorical form:

All things you have not lost are things you have.
All horns are things you have not lost.
∴  All horns are things you have.

This is an AAA-1, and is thus valid. It could just as readily be written as modus ponens: Continue reading Watch your assumptions!