A reductio ad absurdum is a form of argument that attempts to disprove a proposition by demonstrating that its acceptance entails an absurd, contradictory, or unacceptable conclusion. The argument takes the opponent's claim as a premise, derives consequences through valid inference, and shows that at least one consequence is intolerable — thereby inferring the original claim is false. The parameters that define it are: (1) a target proposition to be refuted, (2) a chain of inference that treats the proposition as true, (3) a consequence that is demonstrably absurd or contradictory, and (4) a negation of the target drawn from the intolerable consequence. It persists through teaching, formal logic systems, mathematical proof practice, and argumentative discourse — transmitted in textbooks, deployed in debate, and codified in the rules of reasoning.
Accepted ontology entry
reductio-ad-absurdum
A reductio ad absurdum is a form of argument that attempts to disprove a proposition by demonstrating that its acceptance entails an absurd, contradictory, or unacceptable conclusion. The argument takes the opponent's claim as a premise, d…
Definition
Why it is in scope
A human-constructed argumentative technique in which one accepts an opponent's claim as true, derives its logical consequences, and demonstrates that those consequences are absurd or contradictory — thereby showing the original claim must be false. Built to persist through teaching in logic, philosophy, and formal debate.
Names and aliases
- reductio-ad-absurdumen · CANONICAL
Relations from this entry
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Reductio ad absurdum is designed for the sake of argumentation — its constructed purpose is to further argumentative practice by demonstrating the absurdity of an opponent's position. The servant (reductio) points at the master (argumentation). Per Law 8d: teleology gets its own arrow.
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Remove reasoning and reductio-ad-absurdum stops operating — it is a logical argument technique that requires reasoning as its operational medium. Without the practice of reasoning, the method has no mechanism to function.
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Reductio ad absurdum is a specific argument technique where a proposition is shown to lead to an absurd conclusion, thereby refuting it. It is a recognized form of argument. Argument is the nearest general kind.
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Record identity
- Created
- Jul 29, 2026, 11:45 PM UTC
- Content hash
- 972ea84596c83b555ce363d5ad190c03825d301d63c248de83aa33e01cb72d1a