8.9: Non Sequitur

Suppose you’ve been shopping for a TV set and I tell you not to buy a television set today because it is Tuesday. "Why Tuesday?" you might ask. "Because Tuesdays are so boring," I answer. I have a reason for your not buying the TV set, so I have an argument. But what sort of argument? The reason is so weak that many people are apt to say, "That's no reason at all." My reason may not be totally irrelevant to the issue, but it does not provide significant support for my position on the issue. It would only convince somebody who already was anti-Tuesday or opposed to your purchase, and even if this did convince them it should not convince them. When a conclusion is supported only by weak reasons or by irrelevant reasons, the argument is fallacious and is said to be a non sequitur. This Latin term means "does not follow." Any fallacious argument is one whose conclusion doesn't follow from its supporting reasons, so any fallacious argument is appropriately called a "non sequitur." However, we usually apply the term only when we cannot think of how to label the argument with a more specific fallacy name and when it is fairly easy to show that the reasons are weak.

Sometimes when we say, "That's no reason at all," we do expect to be taken literally, because there really is no reason there. If so, there is no argument, and thus no non sequitur fallacy either. Although there is a fuzzy line between a radically weak argument and no argument at all, there is a difference between the two. The weak one has at least some reasons; the other does not. Here is an example of a disagreement in which a person thinks he is giving an argument but in fact is giving no argument at all:

NON-ARGUMENT: Rafael, you really ought to vote for the Democrat. I just don't understand how you can think of voting for that Republican. I mean, where's your head? The Democrat is so obviously the one to vote for, you should do it and get it over with. Don't sit there and even think about that Republican.

If there were an argument here, the conclusion would be for Rafael to vote for the Democrat. But there is no argument because there is no reason given for the conclusion. Sometimes the term non sequitur is defined more broadly to include a non-argument that is mistakenly put forward as an argument. On that definition, the above non-argument would count as a non sequitur, but we won’t use the term that way.

Here is another example of a passage that you are apt to react to by saying, "That's no argument at all":

NON SEQUITUR ARGUMENT: Nuclear disarmament is a risk, but everything in life involves a risk. Every time you drive in a car you are taking a risk. If you're willing to drive in a car, you should be willing to have disarmament.

At this point you might think, "Hey, that's no reason for disarmament," by which you really mean that it’s not a good reason. All it is saying is that the risks of disarmament are OK because some other risks are OK. Well, some other risks are OK, but some are not OK. So, the reason given is extremely weak.

In summary, whenever you react to a piece of reasoning with a comment such as "Hey, that's no sensible reason for that," you’ve probably detected a non sequitur fallacy.

Exercise \(\PageIndex{1}\)

Is the following argument a non sequitur? If it is, explain why.

Your information shows part of Canada is south of part of California. Therefore, we can be sure that John was right when he said, "Some of Canada is south of part of either California or Nevada."

Answer

It is not a non sequitur because the supposed information would give a good reason to believe the conclusion if it were true. As a matter of fact, the information is true.