From Bo Bennett's excellent website…
Non-Sequitur
(also known as: derailment, “that does not follow”, irrelevant reason, invalid inference, non-support, argument by scenario [form of], false premise [form of], questionable premise [form of])
Description: When the conclusion does not follow from the premises. In more informal reasoning, it can be when what is presented as evidence or reason is irrelevant or adds very little support to the conclusion.
Logical Form:
Claim A is made.
Evidence is presented for Claim A.
Therefore, claim C is true.
Example #1:
Person A: Hmm. I've been reading extracts from this book written by a young earth creationist, and I'm far from convinced the man has a clue what he is talking about. For example he says… "dinosaurs walked on the land and therefore were created on day 6"
Person B: When I read material from young earth creationists, I find it helps if I adjust my frame of reference to a different reality - one where Genesis is literal truth. Then I can see how their ideas work.
Person A: Unfortunately my imagination isn't that good
Person B: Imagine you're in a parallel universe where Genesis is literal truth. It's easy if you try (as John Lennon never said). If the multiverse theory is correct, then such a universe probably exists.
Person C: How about reading and responding to such material specifically in reference to the subject addressed rather than poison the well by an invitation to prejudice regarding other matters?
Explanation: The conclusion from Person C is potentially Argumentum ad Gibberum but even if it did make sense, it does not follow from the premises.
Example #2:
Person A: If God came from something that something is greater and then God is just god (if even that). Then you can ask where the something came from and so on. You have to have an uncaused cause or you end up with infinite regression. That is an incoherent concept.
Person B: An infinite regression might be beyond human imagination but it's not necessarily an incoherent concept. Much of what we've learned about reality in the last 100 years is counter-intuitive and I'm sure many people dismiss it as "incoherent".
Person C: So in other words, you're inviting blind faith in in the assumption that an alternate, as-yet-unexplained-or formulated answer to account for such will emerge?
Explanation: The conclusion from Person C does not follow from the previous comments which were discussing the concept of infinite regress and whether such a concept is incoherent. Person C's contribution seems related to a completely different argument about faith in unproven hypotheses, although it's hard to tell.
Exception: There really is no exceptions to this rule. Any good argument must have a conclusion that follows from the premises.
Tip: One of the best ways to expose non sequiturs is by constructing a valid analogy that exposes the absurdity in the argument.
Variations: There are many forms of non sequiturs including argument by scenario, where an irrelevant scenario is given in an attempt to support the conclusion. Other forms use different rhetorical devices that are irrelevant to the conclusion.
False or questionable premises could be seen as errors in facts, but they can also lead to the conclusion not following, so just keep that in mind, as well.
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