What Is Non Sequitur Fallacy? | Examples & Definitions

Reasoning updated on  May 31, 2024 5 min read

Non sequitur fallacies, also known as formal fallacies, occur when a deductive argument has a flawed structure. In arguments that commit non sequitur fallacies, the premises don’t logically imply the conclusion, rendering the argument invalid.

Non sequitur fallacy example
Premise: All poets are writers.

Premise: Some writers are journalists.

Conclusion: Therefore, some poets have journalism degrees.

This example illustrates a type of non sequitur fallacy. The truth of the conclusion, that some poets have journalism degrees, can’t be inferred from the premises. The argument thus fails to meet the standards of deductive reasoning, in which the truth of the premises should necessitate the truth of the conclusion.

All formal fallacies can be considered non sequitur fallacies. However, the term is especially useful for formal fallacies that don’t fall into another named category.

What is a non sequitur?

Non sequitur, from the Latin for “it does not follow,” is an alternative name for a formal logical fallacy, or an error in deductive reasoning that renders an argument invalid.

Although any formal fallacy can be considered a non sequitur, the term is most useful for referring to flawed deductive arguments that don’t fall into a more specific subcategory.

Colloquially, statements that seem unrelated to the topic at hand can also be called non sequiturs (e.g., in a conversation about learning Spanish, someone abruptly changes the topic to bread baking). In this context, the term is used to describe a surprising change of subject, not a logical fallacy. This casual use of the term is best avoided in formal writing to avoid ambiguity.

Comedic non sequiturs involve abrupt changes of subject that are meant to surprise and entertain audiences. This technique is also employed in literature for humorous effect and, at times, to convey deeper meaning.

In various literary genres, non sequiturs can be used to express themes, philosophical viewpoints, or social commentary.

What are non sequiturs fallacies?

A non sequitur, as a formal fallacy, is fallacious because its conclusion does not logically follow from its premises.

In a valid formal argument, if the premises are assumed to be true, the conclusion must also be true. However, in a non sequitur, it’s possible to assume the premises are true and still deny the conclusion without a contradiction.

The fault lies in the argument’s structure, which fails to follow one of the accepted patterns of formal argumentation.

The accepted principles of formal argumentation, known as rules of inference, include modus ponens, modus tollens, and hypothetical syllogism, among others. They provide a framework in which the argument’s premises logically lead to its conclusion.

When a formal argument deviates from these established logical structures, it is fallacious. Formal fallacies, therefore, are errors in the process of logical deduction, not necessarily in the content or truth value of the premises themselves.

How to identify a non sequitur

To identify non sequitur fallacies accurately, it’s helpful to have some background knowledge in formal logic. When evaluating a deductive argument to determine whether it’s valid or invalid, ask the following questions:

  • Could the premises be true and the conclusion false? Imagine a scenario in which the premises are true but the conclusion is false. If such a scenario is conceivable, the argument is invalid and commits a type of non sequitur, or formal fallacy.
  • Is the argument’s structure consistent with the rules of inference? Assess whether the argument follows the rules of inference (i.e., a recognized logical form, such as a syllogism, modus ponens, or modus tollens). In formal logic, deviation from these structures and their rules often indicates that an argument is invalid.
  • Does the argument fall into a more specific category? Determine whether an argument commits a specific, named formal fallacy, such as affirming the consequent, denying the antecedent, or the fallacy of the undistributed middle. If so, give preference to the specific name rather than the more general term non sequitur.

Non sequitur examples

Non sequitur fallacies are most often found in academic disciplines such as philosophy, formal logic, and mathematics, where formal argumentation is essential.

Examples of non sequitur fallacies are relatively difficult to find in the media, politics, or day-to-day conversations because they typically occur in deductive, formal arguments. However, they may also surface in contexts like legal arguments and debates.

Non sequitur fallacy example in criminal law
Premise: If the defendant is the killer, then the murder weapon should have the defendant’s fingerprints.

Premise: The murder weapon does have the defendant’s fingerprints.

Conclusion: Therefore, the defendant is the killer.

This argument commits a non sequitur fallacy because even if the premises are true, they don’t logically necessitate the conclusion. It’s possible that the defendant touched the gun at some point in time but didn’t kill anyone. Because both premises could be true, and yet the conclusion could still be false, the argument has a fallacious structure.

The term non sequitur has a distinct meaning in literature and performance art, where instead of a logical fallacy, it refers to an absurd twist in language or plot that subverts expectations.

Comedic non sequiturs are unexpected, sometimes illogical statements or punchlines that take unexpected and often absurd turns, deviating from the expected flow of conversation or plot.

Non sequitur example in comedy: Groucho Marx
The art of comedic non sequitur is exemplified in many of the humorous lines attributed to Groucho Marx:

“I never forget a face—but I’m going to make an exception in your case.”

“Time flies like an arrow; fruit flies like a banana.”

“One morning I shot an elephant in my pajamas. How he got in my pajamas, I don't know.”

Groucho Marx’s comedic strategy relied heavily on non sequitur humor in the form of paraprosdokian, a figure of speech in which the latter part of a sentence or phrase is surprising or unexpected, playfully subverting the initial part of the joke.

In addition to serving as a comedic device, non sequiturs can be found in literature in the form of absurd, unexpected turns in language or plots that add depth and complexity to a narrative. Literary non sequiturs challenge the expectations of conventional storytelling and invite readers to seek multiple layers of meaning.

Non sequiturs are often used in genres such as novels, plays, and poetry to explore themes of existentialism, nihilism, absurdity, and societal critique.

Non sequitur example in literature
Alice: But I don't want to go among mad people.

Queen of Hearts: Oh, you can't help that. Most everyone's mad here.

Alice: Why, you're not a bit like what you were when we first met, and you were so nice, just a minute ago!

Queen of Hearts: Off with their heads!

In Alice’s Adventures in Wonderland, Lewis Carroll has the Queen of Hearts interject “Off with their heads!” in unexpected contexts. This non sequitur is comedic, adding to the whimsical humor of Wonderland, but it also satirizes the absurdity of authoritarian rulers.

Do you want to know more about common mistakes, commonly confused words, or other language topics? Check out some of our other language articles full of examples and quizzes.


Rhetoric

Commonly confused words

Fallacies

Symbolism

Possum vs opossum

Straw man fallacy

Play on words

Weather vs whether

Post hoc fallacy

Juxtaposition

Inter vs intra

Fallacy of composition

Paronomasia

To vs too

Tu quoque fallacy

Allusion

Subjective vs objective

Either-or fallacy


Frequently asked questions about non sequitur fallacy

What is the difference between the post hoc fallacy and the non sequitur fallacy?

Post hoc and non sequitur fallacies both involve the concept of “following.” However, post hoc fallacies are related to the chronological sequence of events, whereas non sequitur fallacies are related to the logical connection between statements.

To accurately distinguish between the two fallacies, assess whether the argument’s focus is chronological (post hoc) or logical (non sequitur).

What is an example of non sequitur?

Examples of non sequitur fallacies, also known as formal fallacies, aren’t easy to find in daily life because they typically occur in formal disciplines such as logic, mathematics, and physics. The following example illustrates the nature of a non sequitur fallacy:

Premise: All cats are mammals.
Premise: A dog is a mammal.
Conclusion: Therefore, a dog is a cat.

More specifically, this example falls into the subcategory of the fallacy of the undistributed middle, in which the middle term in the premises doesn’t cover all possible cases, leading to a faulty conclusion.



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Magedah Shabo

Magedah is an author, editor, and educator who has empowered thousands of students to become better writers.

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