Identifying and Arguing Against Reductio ad Absurdum (1/2)

A common mode of argument is formally called reductio ad absurdum. The point of this is to take your opponents’ arguments and show absurd conclusions that follow from those arguments. The point of the reductio is quite obviously to argue from the absurd conclusions to an error in prior arguments. The goal is generally not to get the person to accept the absurd conclusions as good ideas.

I have seen some misunderstand this argument recently. So, I wrote these two short pieces. This first one will explain reductio ad absurdum and the second one will talk about the application where I see people not getting it. This piece has three brief points. The argument, ways (not) to argue against it, and examples.

A summary of reductio ad absurdum

Reductio Ad Absurdum by John Pettie (CC0)

Merriam Webster defines this as: “disproof of a proposition by showing an absurdity to which it leads when carried to its logical conclusion.” It is a form of argument that has been around for at least 2500 in Greek philosophy according to Wikipedia.

The degree of absurdity can vary from self-contradiction to falsehood to untenable positions to highly implausible realities. I encounter the untenable or highly improbable more often in debates about things in the messy real world.

A reductio is obviously an indirect proof for the opposite. Logically, it only implies the exact opposite but can often be implied to a much wider opposite or used in such a case. Like if a debate is whether the dress is gold and white or black and blue, if one were to show there is no gold pigment, one would show it was therefore not gold and white: black and blue would then likely be implied, but that has not been logically proven.

How to argue against reductio ad absurdum

Against a reductio ad absurdum, one needs a strong argument. I can see three types. First, one could argue why the two are completely unlike. A second way to argue against it would be to significantly qualify the original statement. Finally, one can point out how the logic fails.

You can’t simply argue around the edges. Unless the technicality changes the nature of the whole argument, it is not an argument that gets defeated on technicalities. If the consequences of an argument are almost as ridiculous as the original claim by the interlocutor, it is still pretty ridiculous.

Often it is highly unwise to embrace the conclusions of the reductio. Your interlocutor was pointing out absurd conclusions of your position so you might change it. They generally don’t want you to become absurd but change your position.

Two Examples


ThoughtCo gives this example from William Harmon and Hugh Holman: “One might say, for instance that the more sleep one gets the healthier one is, and then, by the logical reductio ad absurdum process, someone would be sure to point out that, on such a premise, one who has sleeping sickness and sleeps for months on end is really in the best of health.”

A response to that may be to clarify the original statement to add both “on average” and “up to about 8-8.5 hours a night,” or similar. I’m not going to get into the details on how much sleep we need but something like that seems about right from the medical stuff I’ve seen.

Wealth Tax

Person A: “I agree with a wealth tax.”

Person B: “But if we taxed wealth at the same rates as income, homeowners would lose their homes to taxes and small business owners would lose their businesses. It would be horrible for the economy.”

Person A can then respond with something like, “Not the same rates as income tax. I would suggest something like 1% on wealth over 100 million. So that reductio ad absurdum makes no sense.” (This is closer to what those proposing a wealth tax are proposing. This is not the place to debate its prudence but something like that is not subject to this reductio ad absurdum.)

It would be pretty pointless for person A to argue that they would have rates 25% less than income tax. That would save some homeowners and small business owners, but still be trouble for a huge majority.


Reductio ad absurdum is a common type of argument that shows – or attempts to show – the error of an opposing position by drawing out conclusions from their argument. To respond with something around the edges does not really answer the argument. All that doe sis show your argument is not quite as ridiculous as your interlocutor said. Instead, you need to prove a complete difference, logical incoherence, or qualification to your original statement.

Update: Part 2 is live.
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