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June 23, 2020

False Syllogisms

Avoid them as you would the flu.

“I was in the store,“  our friend said, “when someone came up to me and said ‘you’re wearing a mask so you must be a Democrat’. Isn’t that ridiculous.”

MaskedmeIt’s not only ridiculous, it’s also a false syllogism. Even if you know nothing about flu and masks and Democrats and Republicans, you can spot the bad logic. Even if all Democrats wore masks, everyone who wears a mask doesn’t have to be a Democrat. My avatar is an example since I’m not a Democrat and my avatar as drawn by grandson Jack is masked.

Long before misinformation was spread wholesale on the web, even before the printing press, Aristotle studied logic including syllogisms, presumably so he could judge the conclusions he heard at the forum when he did not have enough facts of his own.

A syllogism can be a very good way to reach a conclusion from observations (or to make logic puzzles). Lewis Carroll, author of Alice in Wonderland, gives this intentionally trivial example.
(1) Babies are illogical;
(2) Nobody is despised who can manage a crocodile;
(3) Illogical persons are despised.

A conclusion you can confidently draw from these premises is that no babies can manage crocodiles, useful if you’re hiring crocodile managers. Granddaughter Lily and I are studying syllogisms via Skype not only in order to visit during lockdown but also because she likes puzzles and I’d like her to be able to spot bad logic.

At the Mad Hatter’s Tea Party, several characters give great examples of false syllogisms:

… said the Hatter. `You might just as well say that "I see what I eat" is the same thing as "I eat what I see"!'

`You might just as well say,' added the March Hare, `that "I like what I get" is the same thing as "I get what I like"!'

`You might just as well say,' added the Dormouse, who seemed to be talking in his sleep, `that "I breathe when I sleep" is the same thing as "I sleep when I breathe"!'

If we have the facts: (1) no one has been known to get the flu twice and (2) Joan currently has the flu, we can reason correctly that Joan is not known to have had the flu previously. We cannot conclude that Joan has not had the flu previously; perhaps she and many other did have the flu but that history is still unknown. This may sound like hairsplitting, but logic is essential to useful science. It’s also very useful in a democracy even if often ignored. When we know that none of millions of C19cases are reinfections in the same person, we will know that we can and should act as if no one can get the flu twice… but we still won’t know that reinfection will never happen.

The same friend who told us being identified as a Democrat by her mask went on to say that that it’s appalling how many Trump supporters in the grocery store aren’t masked. “How do you know they’re Trump supporters?” I asked.

“They’re not wearing masks.”

Apparently use of false syllogisms is non-partisan.

See also:

DIY Truth-Checking

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