Speaking of Logic

Figarist David Kaufmann put us on to a great fallacies site. Fun and useful, even while it implies that fallacies are a sin. So do we, in Thank You for Arguing. But in rhetoric, the real sinner in a fallacy is the person who falls for it. Rhetoric has few rules. If you can persuade without threats or actual violence, you’re good.

As we note in our book, most fallacies come down to one or more of these three elements:

Bad proof. This includes false comparisons, bad examples, and ignorance as proof (assering that the lack of examples proves something). The tests didn’t find anything, so you’re not sick.

Wrong number of choices, offering just two choices when more are actually available, or merging two or three issues into one. We can bomb Iran, or we can let them destroy Israel.

Disconnect between proof and conclusion. The tautology—in which the proof and the conclusion are identical—constitutes the most infamous disconnect. He’s good at sports because he’s an athlete.

Our favorite fallacious quote comes from the great Homer Simpson. When he offers his daughter, Lisa, a doughnut, she asks if he has any fruit instead. “This has purple in it,” Homer replies. “Purple is a fruit.”

Can you name the fallacy?

Comments

[John Hritz]

Homer is assuming either that all purple things are fruit or that all fruit are purple neither of which is true, ergo a form of bad proof.

[Derpy]

@John: that's not actually correct. Homer isn't doing either of those things; he's asserting that "purple" is itself the name of a fruit rather than (or in addition to) a color, similar to e.g. "orange".

[Jennifer]

I call "bad proof".

[Figaro]

Getting there! Any other takers?

[Marco]

I would say it's a tautology.

[Conan]

Hey, is this like "Name that Tune"? I can name that fallacy in...

My initial impression is that Homer commits the fallacy of faulty generalization. To quote Alexander Dumas - "All generalizations are dangerous, even this one".

But it seems somewhere on Fig's site this Homerism is classified as an enthymeme, the rhetorical syllogism. If it is put in syllogistic form it would go like this:

This donut has purple in it.
Some fruit is colored purple.
Therefore, all things colored purple is a fruit.

So, OK, I'd say Homer is singing an enthymeme in the key of a faulty generalization.

[Jared Nathan]

I will say that it seems like a bad proof of the false comparison variety.

He starts with a false premise, that purple is a fruit, however this does not necessarily mean that it is an invalid argument (in the logic sense). If I assume that his premise is true, the conclusion can be reasoned to be false. And that would make the argument illogical.

It is a non sequitur. Homer's issue is that he falsely concludes that two things which share a common property are therefore identical. Purple is fruit, the donut has purple (fruit) in it, therefore the donut is fruit. It’s like me declaring; I am a human, I swallow a piece of jelly donut so that it is in me, and therefore I am a jelly donut. (I couldn’t help myself from the ich bin ein Berliner…)

Jay Heinrich has referred to this as the “all natural fallacy”, which assumes that members of the same family share all the same traits. I would not like to say this is an example of hasty generalization, since it is my understanding that has to at least start with a true premise which is then applied so broadly that it reaches a false conclusion. Here, we do indeed have a false premise.

However, my question is: Is the “all natural fallacy” similar to metonymy? Specifically, can I say ANF is similiar to synecdoche? Synecdoche has many meanings, but one of them is “a part referring to the whole”, pars pro toto (totum pro parte is another example). I can see how they are not the same, since metonymy is a figure of speech, but am I making a hasty generalization in reasoning that they are similar?