Non-Sequitur

When you hear the term “non-sequitur,” you probably think of an absurd statement or conclusion that someone splices into a conversation. This is what you might call the use of non-sequitur in the vernacular. However, as a rhetorical fallacy (sometimes also called logical fallacy), a non-sequitur is a little different from that. It has a certain form and contains a certain error.

Non-Sequitur Definition

Non-sequitur is a logical fallacy. A fallacy is an error of some kind.

The non-sequitur is also called a formal fallacy. This is because there is an unmistakable gap between the evidence and the conclusion drawn from that evidence; it is an error in how the argument is formed.

Because a non-sequitur lacks clear logic, it is easy to identify.

Non-Sequitur Argument

To illustrate the non-sequitur at the most basic level, here is an extreme and perhaps familiar-sounding example.

This might be similar to the kind of non-sequitur you expect: something out of the blue and way off-topic. However, even in this example, a non-sequitur connects evidence to a conclusion. This example simply connects evidence to a conclusion without any logic.

Fig. 1 - A non-sequitur flat out does not follow.

Here is a less absurd example of a non-sequitur.

This is absurd, too, but it’s not nearly as absurd as the first non-sequitur. Regardless of severity, all non-sequiturs are to some degree absurd, and there’s a reason for that, which comes down to it being a formal fallacy.

Non-Sequitur Reasoning: Why it’s a Logical Fallacy

A non-sequitur is a type of formal fallacy. To understand what that means, you should familiarize yourself with the more common informal fallacy.

Here is an example of an informal fallacy.

The premise here is "all things need water to grow." This is not true—not all things need water to grow—so the conclusion cannot be true.

On the other hand, a non-sequitur fails because of a gap in logic. Here's an example.

Here, no formal logic links the premise to the conclusion since a rock is not a plant.

Here is how a non-sequitur becomes an informal fallacy again.

Do you see how this new piece of logic connects the premise to the conclusion? This latest example would again be an example of an informal fallacy, where the root cause is the lack of truth in the premise (that rocks are plants), not the lack of formal logic.

Non-Sequitur Example (Essay)

Here is how a non-sequitur might sneak into an essay.

This example is short because almost any additional reasoning would turn this non-sequitur into an informal fallacy. Currently, this argument is as follows:

Hans attacks a diner at random, and therefore he commits a murder.

This is a non-sequitur because the conclusion does not follow the premise. However, it would not take much to make the conclusion falsely follow the premise. Here's how you could turn this non-sequitur into a faulty analogy (a kind of informal fallacy).

Hans attacks a diner at random, which is an unexpected and dangerous thing. Because Hans is capable of unexpected and dangerous things, he commits a murder, which is also an unexpected and dangerous thing.

This argument attempts to say that because murder and attacking a diner are both “unexpected and dangerous,” they are comparable. They are not, of course, which makes this a faulty analogy.

This second example is also an example of an ad hominem fallacy. An ad hominem fallacy casts blame on someone due to their character.

Fig. 2 - To avoid a non-sequitur, establish real evidence that implicates Hans.

When you identify logical fallacies, always start by breaking the argument down into its premise(s) and its conclusion. From there, you will be able to determine whether the argument contains a formal fallacy or an informal fallacy and what specific fallacy or fallacies it contains.

How to Avoid the Non-sequitur

To avoid a non-sequitur, don't leave out any steps of your argument. Be sure that none of your arguments are implied, assumed, or otherwise taken for granted.

Spell your logic out on the page. Follow a line of reasoning!

Finally, don't get smart. Although you can use a non-sequitur to be funny, you do not want your argument to be funny or absurd; you want it to be valid.

Non-Sequitur Synonyms

In English, non-sequitur means “it does not follow.”

A non-sequitur can also be called an irrelevant reason, a false premise, or derailment. It is the same as a formal fallacy.

Non-sequitur vs. Missing the Point

A non-sequitur is not synonymous with missing the point, which is an informal fallacy. Missing the point occurs when an arguer attempts to counter a point that is not contained within the original argument.

Here is a brief example in which Person B misses the point.

Person B misses the point because Person A is arguing against damaging natural woodlands period. Solving the CO₂ problem is not the point. This is different from a non-sequitur because Person B's logic is valid at least in a vacuum, whereas no part of a non-sequitur is valid.

Non-sequitur vs. Post Hoc Argument

A non-sequitur is not synonymous with a post hoc argument, an informal fallacy. A post-hoc argument asserts a cause using correlation.

Here is a brief example.

In reality, Fredegar could have gotten depressed for a thousand other reasons. Nothing about this evidence shows cause, merely correlation.

While a post hoc argument asserts a cause using correlation, a non-sequitur asserts a cause using nothing.