Wars of the Absurdums
A reductio ad absurdum — I’ll call it “RAA” for short — is when you argue against someone’s claim X by showing that, if X was true, something obviously absurd would also be true.
In other words, as illustrated in the above image, “If the premise was true, the logical implications would be crazy.”
Lisa and George’s Thermometer Collection
Lisa and George are watching it rain.
“Gross, rainy weather lately,” says Lisa. “How cold do you think it is out there?” asks Lisa.
“Maybe 25, 30,” replies George, speaking Fahrenheit.
“What!?” Lisa exclaims. “If it were that cold, it’d be snowing, and we’d be hallucinating! And that’s absurd!”
Pretty straightforward, right? It’s absurd that they’re both hallucinating the rain, and so it mustn’t be 25-30 degrees; 32 is the freezing point in Fahrenheit.
“Alright, let’s check,” says George. They walk out to the back porch and look at the thermometer outside. “See?”
Just as George guessed, it was 29 degrees outside.
“The thermometer must be broken,” said Lisa. “Let’s check the one we have on the front porch.” But, sure enough, the front porch thermometer said 29, too.
Same with the thermometer just outside the kitchen window.
“They can’t all be broken in exactly the same way,” says George. “That’d be absurd.”
It turns out that, from the outset, Lisa was unaware of the fact that temperature can vary in different layers of atmosphere. If it’s warmer above the surface, rainfall may not have time to freeze before hitting the ground, even though it’s passing through a sub-freezing layer.
In other words, learning more about how the world works and doesn’t work can make the difference between some RAA being thought false versus true.
Furthermore, sometimes RAAs are just “non sequiturs,” which means that they don’t logically follow, e.g., “If it was 25-30 degrees outside, all morality would be invalid.”
That’s an obvious one, but non sequiturs are often very subtle. Recognizing non sequiturs where they exist can also make the difference between some RAA being thought false versus true. My own record is spotted with many infractions for criminally using non sequitur RAAs! But I’ve done my share of repentance. (And this is my penance.)
Earlier, I wrote about a specific kind of non sequitur — where you think the world is “too rocked” by a world-rocking revelation — and called it “Kochab’s Error.” Kochab’s Error is often used in an attempt to argue ad absurdum.