Concepts & Ascents

One of the most commonly used tactics in debate is the reductio ad absurdum. The Latin phrase, rendered into English as “reduction to absurdity,” is a dialectical move by which one interlocutor assumes the truth of his opponent’s claim to show that it would lead to an absurd conclusion. This conclusion may be a contradiction or a claim that the opponent is unwilling to accept — oftentimes both.

The easiest way to understand the method is to observe it in action, for it is a highly practical tool which, when grasped by example, becomes much more useful than the theoretical background. We will look at two examples of the reductio ad absurdum, each followed by consideration of its merits, demerits, and how its implementation can be made systematic.

Example #1

Roger: “Only scientific knowledge counts as real knowledge.”

Lucy: “What do you mean by ‘scientific knowledge’?”

Roger: “Knowledge obtained using the scientific method.”

Lucy: “Did you obtain this knowledge using the scientific method?”

Roger: “No.”

Lucy: “Then, by your own claim that only scientific knowledge counts as real knowledge, we must conclude that your statement itself is not knowledge.”

Example #2

Lucy: “Reason must always be subordinate to revelation.”

Roger: “What do you mean by that?”

Lucy: “That revelation must be interpreted literally, not metaphorically.”

Roger: “Is that because a metaphorical reading prioritizes reason by reinterpreting passages that, when read literally, would lead to contradictions?”

Lucy: “That is what I mean.”

Roger: “And did we not just give a reason why we should read passages literally?”

Lucy: “We did.”

Roger: “So we used reason to determine the manner in which we should engage with revelation?”

Lucy: “Correct.”

Roger: “And this was a correct decision?”

Lucy: “I would say so.”

Roger: “Then would you agree that our previous decision was a way of subordinating revelation to reason?”

Lucy: “I have no choice but to agree.”

Roger: “Strange indeed. Just recently, we were of the opinion that reason must be subordinate to revelation, but it seems that all this time we have been subordinating revelation to reason.”

Lucy: “Strange indeed. What should we do about it?”

Roger: “Let us simply conclude that reason is subordinate to revelation and revelation to reason.”

Lucy: “You wish for something impossible. We have arrived at contradictory beliefs. Thankfully, they are not exhaustive of all possible positions, but we must discard at least one of them; otherwise, we will be — metaphorically, of course — ‘of two minds.’”

Merits

As seen, most of the work is done through questions rather than assertions. This is the first merit of the reductio: it is low-risk. You do not have to expose your own beliefs to scrutiny but instead operate on your opponent’s material. It is a kind of mental judo—you use your opponent’s weight against them, without committing yourself to a positive doctrine.

Demerits and Systematization

A common critique of the reductio ad absurdum is that it can appear unsystematic or opportunistic. How did Roger know which questions to ask? What guided him toward the contradiction? The following guidelines help make the method more deliberate:

• Identify self-referential inconsistency: When the act of asserting a claim contradicts its content. Example: “Reason must always be subordinate to revelation” is justified by reason itself, thereby subordinating revelation to reason.
• Look for exceptions to the rule: When a claim, if applied to itself, invalidates itself. Example: “Only knowledge obtained through the scientific method counts as real knowledge.” If that rule is applied to itself, the statement is not real knowledge, since it wasn’t derived by experiment.

Conclusion

By consciously attending to these patterns, one can move beyond spontaneous cleverness and make the reductio ad absurdum a systematic and precise dialectical weapon. There is much more to say on the topic, but this introduction has hopefully shown that the reductio ad absurdum is an effective method to use both on yourself, and in conversation with others. It is a way of refining thought until only what is internally consistent remains.