Simple question. Is every fallacy a non-sequitur at its most fundamental basic?

For example, take a strawman argument. Here, one attacks a misrepresentation of somebody else's argument. But, fundamentally speaking, one is thus "concluding" that one has provided an accurate counter-example, but that does not "not follow" from the "premise" that one has argued against a misrepresentation.

Hence, this seems to be non sequitur, as one attempts to take the premise of attacking a different argument, and concludes that this is an adequate response. Which does not follow, as one has not proven that the argument one has attacked is actually the argument the other person laid forward.

So, is every other fallacy also fundamentally non sequitur?

  • It depends on your intention in diagnosing fallacies. Every deductive step that is not a valid inference is by definition a non-sequitur. That includes every fallacy. But that means that describing something as a non-sequitur is not a very useful way of helping the person making the argument see their mistake. They think it follows, or they would not have said it. Further evidence of error is needed. We generally only fall back on the overly-broad term when we can't be any more helpful, or when we consider the problem obvious.
    – user9166
    Oct 10 '17 at 17:26
  • See Wikipedia's non-sequitur:"the term 'non sequitur' typically refers to those types of invalid arguments which do not constitute logical fallacies covered by particular terms (e.g. affirming the consequent). In other words, in practice, 'non sequitur' refers to an unnamed logical fallacy. Often, in fact, 'non sequitur' is used when an irrelevancy is showing up in the conclusion."
    – Conifold
    Oct 10 '17 at 19:37

Aristotle is said to have asserted that all fallacious arguments essentially commit Ignoratio elenchi (= ignorance of argumentation or missing the point for moderners). Since some logicians categorize ignoratio elenchi under the non sequitur (= does not follow), we could say that your observation that all fallacies are essentially non sequitur is right.

The problem with your assertion however is that scholars deeply disagree on the categorizations of fallacies and the scope of each fallacy. They cannot even offer a precise definition for 'fallacy': at most they agree that a fallacy is a defect in reasoning. Even Aristotle himself used ignoratio elenchi in the above broadest sense and a very narrow sense where the concussion simply is irrelevant to the premises, which is neither a straw man nor a red herring (e.g., "Abuse of the welfare system is rampant nowadays. The conclusion is obvious: we must abolish the system altogether.") Presently, Non sequitur is usually limited to the cases that produce a comical effect due to breaking the cliche or expectations: e.g., "My wife and I were happy for 20 years....Then we met."

Formal logic has been unhelpful to understand fallacies since many perfectly valid arguments are fallacious. Informal logic that is informed by critical thinking, rhetorics, communications and AI have been far more helpful to understand the categorization of fallacies. Under the informal logic, it is now clear that many fallacies are fallacies for the reason other than relevance (broadly, non sequitur): e.g., weak induction, illicit presumptions. Viewed in this light, your assertion can be said to be false.


Since Wikipedia sucks, I went to Meriam-Webster instead, which gives two definitions:

  • an inference that does not follow from the premises; specifically: a fallacy resulting from a simple conversion of a universal affirmative proposition or from the transposition of a condition and its consequent

  • a statement (such as a response) that does not follow logically from or is not clearly related to anything previously said:

"We were talking about the new restaurant when she threw in some non sequitur about her dog."

I'm more familiar with the second definition, but the first definition seems to support the statement "all logical fallacies are non-sequiturs". However, the "specifically" part seems to indicate only specific fallacies are considered non-sequitirs.

Interestingly, when non-sequitur was Word of the Day, the specificity criterion is missing.

The Oxford Reference defines it as " argument in which the conclusion does not follow from the premises", not limiting it to specific fallacies, and two online dictionaries agree:

  • dictionary.com defines it as "an inference or a conclusion that does not follow from the premises", without any specificity conditions.

  • Wiktionary's second and third definitions are "Any invalid argument in which the conclusion cannot be logically deduced from the premises; a logical fallacy" and "A statement that does not logically follow a statement that came before it", again not mention a specific fallcy.

On the whole, I'd say "every logical fallacy is a non-sequitur" is a reasonable statement.

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