Quora Answer: What is a Non Sequitur Argument?

The following is my answer to a Quora question: “What is a non sequitur argument?” 

“Non sequitur”, from the Latin “it does not follow”, is a logical fallacy.  Aristotle wrote a treatise on deductive reasoning, Ἀναλυτικὰ Πρότερα, translated into Latin as Analytica Priora.  In English, we know this work as “Prior Analytics”.  In it, he covered several types of logical fallacies, including the non sequitur argument. 

For example, if a dog is an animal, therefore, all dogs are animals.  If all dogs are animals, therefore, all animals are dogs.  This type of non sequitur is known as affirming the consequent.  Even were the premise and the conclusion to hold true, the consequence is not predicated on the premise.  It would be a coincidence. 

Taking this further, another example of a non sequitur argument would be the claim that since dogs are animals, and cats are animals, therefore cats are dogs.  Here, the conclusion is still independent of the premise. 

Another example of a non sequitur argument would be the opposite, denying the antecedent.  For example, cats are animals.  Dogs are also animals.  Cats are not dogs.  Dogs are not cats.  Therefore, neither are animals.  We could use an example where the conclusion may be true, but the premise would still be false.  For example, I am Singaporean.  I am Eurasian.  If I am not Eurasian, I am not Singaporean.  It could be true, but the two points are unrelated. 

There are half a dozen or so different examples of non sequitur arguments.  In any formal contention, where the premise or the conclusion are unrelated, then the position arrived at, even if it were true, would only be true by coincidence, and not arrived at by logic.