Reductio ad absurdum is Latin for ‘reduction to absurdity’ – a method of reasoning that originates from classical Greek philosophy. Its use is common in debates, philosophy, and in formal mathematics (where it is referred to as proof by contradiction). Consider the examples below:
Example 1: Is intelligence determined by genes or the environment?
Let’s say someone is arguing that intelligence is 100 percent determined by genes. You can counter this with reductio ad absurdum:
If intelligence were only determined by genes, then someone raised without human contact or knowledge could still be a genius.
On the other hand, if someone were to argue that intelligence is 100 percent determined by the environment, upbringing and hard work, you could counter that argument as follows:
If intelligence is 100 percent determined by the environment, show me a professor who contributes to his field, despite having down syndrome (a form of intellectual disability).
Example 2: What is the smallest number ever?
If someone told you that they had discovered the smallest positive number in the world, you could easily disprove their claim as follows:
There can be no ‘smallest positive number’, because whatever that number is, you can divide it by 2 and get a smaller number!
But Watch out for straw man arguments!
Reductio ad absurdum can be an effective way of disproving or proving claims, but use it with caution. You have to be wary of straw man arguments – situations where the contradiction is made out of ignorance and without full appreciation of the specific assertions in a claim.
For instance, a person who believes the world was created would be inaccurate to argue against the theory of evolution as follows:
If evolution were true, we would be seeing monkeys turning into humans all the time.
The above is a straw man argument (and the wrong use of reductio ad absurdum) because it takes an extreme view of evolution and ignores the fact that evolution is a process that spans millions of years!
Further Reading and References: