Logical Fallacy #16: Reductio ad absurdum

This fallacy translates from Latin to “reduction to absurdity”, but comes from the Greek “eis atopon apagoge” which means “reduction to the impossible”. If you reduce an argument too far, it becomes absurd, or blatantly wrong. Clearly any argument can be rendered in a similar light, so using this technique to demonstrate that an argument is true or false is illogical. If an argument has an absurd conclusion to prove the premise, the odds are the arguer has reduced the argument to absurdity.

There are three flavours of this logical fallacy.

– Undeniable:

Consider these two arguments:

* If the anvil had no weight, it would rise up float away.

* The Bible is the word of God, so it cannot be corrupted by man.

The first argument seems reasonable as a massless anvil would be buoyant and would potentially float. As it does not do so the assertion of mass in the anvil must be true.

The second argument also seems reasonable, if the Christian Bible is the word of the Christian God, then it cannot be corrupted by man. Yet closer examination will show that this statement is actually quite in error. Firstly, there is no evidence that the bible is the word of god, especially given all of the varying versions, interpretations, errors and contradictions found in the bible. This does not stop this argument being used though.

– Untenable result:

Consider these two arguments

* Without rules, society would become chaos

* Without religion, humans would have no morality

Both arguments seems similar and perhaps true. A society without rules would seem quite chaotic, yet when instances of this have occurred, the chaos is often brief before some kind of rule set becomes imposed by the people themselves. Even in the chaos, some sets of rules can be found. While not necessarily true in all cases, the first argument seems reasonable as a general rule of thumb.

The second argument appears to be basically the same thing, yet morality has been demonstrated to be irrelevant to religion and belief systems. Examples of theists and a-theists are available demonstrating both moral and amoral behaviour.

– Proof by contradiction:

Consider this statement

There is no smallest positive rational number, because if there were, it could be divided by two to get a smaller one (taken from the Wikipedia example)

This argument relies on the inability to contradict the premise. If you can, contradict the argument, then the argument is false. The problem is this relies on everything being true or false and negates fuzzy logic and alternate measuring systems. When does a table become a stool, or a stool a table? Does it have to be one or the other, is hybridisation possible, or does function define the form?

Common Examples from Both Sides

Here are two common absurd examples created by over reduction.


Evolution is quite a large and complex concept. It is frequently reduced to a digestible level to give the basic idea to the lay person. Pretty much every lay person gets that basic idea:

A while ago humans came from apes, a long time ago we came from slime. Life changes. Changes that add strength survive, the others die out

It’s a nice, tidy concept. Of course, the above is ridiculously simplified. People spend their entire careers studying and refining this concept in many different fields of study.

The fallacy comes in when this reduced concept is then used to attack and defend the complex idea. At this point, the reduced concept become an absurd argument.

Climate Change or Global Warming

Like Evolution, Global Warming (which is a more accurate description) is a big and complicated concept that is simplified for the lay person. Most lay people get this basic description:

The gradual additional energy the Earth is retaining due to additional anthropogenic (man caused) and natural phenomena increasing the so called “Green House Gases” (blanket gases), often simplified to CO2 (Carbon Dioxide).

Again, it is a nice and tidy concept. When it falls down is when this reduced concept is used to try to attack and defend the full complex concept developed by thousands of scientists using millions and possibly billions of points of data to explain the never before done experiment of what happens when we humans change the ratio of energy into our planet from the sun to energy out. At this point, the reduced concept become an absurd argument.