Talk:Non sequitur (logic)

If and only if
I may be nitpicking here, but according to the article, if either of the given examples had "If and only if A, then B" as their first premise, then they would be valid and non-fallacious. I would agree that they would no longer be non sequiturs, but surely they would still be non-valid and fallacious, because "If and only if I am a cat, I am a mammal." and "If and only if I am in Tokyo, I am in Japan." are both false premises - i.e., cats are not the only mammals, and Tokyo is not the only location in Japan.


 * Actually, the article is correct, in the sense that its logic is correct. According to the definition of valid they are true as well.  valid just means that you can write the deduction as an if statement that is always true--and recall that if the premise of an if statement is false, the statement itself is still true.  So, to test the validity on one of the examples, we would write  "If (if and only if I am a cat, I am a mammal) and (I am a mammal), then (I am a cat)" is clearly true, even when the first premise of the statement is false.  Validity has to do with the soundness of the logic, not the truthfulness of its premises.  Furthermore, since fallacies are errors in the logic of a deduction, the claim of non-fallaciousness also holds.


 * A hyperbolic example of non sequitur logic would be, "A bus is going through Wetumpka, Alabama. At the first stop, 3 three people get on. At the next one, 12 people get on and 2 get off. After that 5 more people get on. What is the bus driver's name?".  — Preceding unsigned comment added by Mastermike14 (talk • contribs) 05:27, 21 September 2011 (UTC)


 * Basically, the aforementioned arguments would be valid and non-fallacious but also unsound. Shawnc 11:00, 29 January 2006 (UTC)


 * As far as I can tell, it sounds as if the non-sequitur argument would be correct if the initial premise (A) is the only possible premise that would lead to (B). We have to assume that that "If and only if A" is true for a non-sequitur to be correct logic.  That is the reason why a non-sequitur is false; this assumption that "If and only if A, then B" is true.  Though not stated in the logic of a non-sequitur, this is the main problem.  The fact that a non-sequitur assumes the "If and only if" condition is what makes it false...the way to correct it (a point that the first commenter missed) is not only to merely change the reasoning, but also to change the fact itself.

I'm arguing against my instinct here, but should that jab about advertising be in there, without a link to at least one advert that exemplifies a non-sequitur in a non-humourous manner? Offhand I can't think of one that could be linked to, but without that, it's a bit of ad hominem without any supporting reference. 82.40.136.135 20:49, 12 February 2006 (UTC)

Ok, let me clarify the If and only if part. I will use IFF to denote If and only if. IFF can only be used if a conjecture AND its converse will both be true. Thus, I am a cat IFF I am a mammal is NOT true. Even though it may sound to be true, the "only" in IFF makes it untrue. IFF is and has always been used like this. Also, I am new, however shouldn't the fallacy of the converse be included in this?74.236.46.160 (talk) 00:27, 9 April 2010 (UTC)

Other uses
The American Heritage Dictionary also defines non-sequitur as a statement for which no response is appropriate or reasonable. Should that definition be included in this article? Fishhead64 22:54, 17 July 2006 (UTC)

More on everyday non-sequiturs?
The disambiguation page suggests a non-sequitur is either a) absurd/comical or b) formally illogical. In other words, you find non-sequiturs either in a deliberately humourous or logical context. Most non-sequiturs, however, crop up in everyday speech or argument where people frame their arguments poorly in the heat of the moment. These ordinary non-sequiturs are neither intentionally absurd/comical nor statements of formal logic -- they're just everyday slips or, in the case of political statements, carefully calculated "weasel words". The last part of this article (after the formal logic bit) touches on this.

I feel that "everyday non-sequiturs" need to be covered more extensively. There are lots of examples in advertising and political speeches. There are also examples in psychology, where a person's tendency to conclude things about themselves that "don't follow" leads to depression or other forms of mental illness. This is what the "hair" example alludes to, but there's much more to say. Untangling non-sequiturs is one goal of psychiatric treatments like cognitive therapy. Marcusswann 10:48, 14 November 2006 (UTC)

Example 1
Example one I think could be more concise.

1. If A is true, then B is true. 2. B is stated to be true. 3. Therefore, A must be true.

Would be better if you said

1. All bananas are fruits. 2. This is a fruit. 3. Therefore, this fruit is a banana.

If you would rather A's and B's just substitute them in. An explaination could be:

1. All A's are B's.  2. This is a B.   3. Therefore, this must be an A.

A's are a subset of B's from premise one; however, no mention is made of the subset of B's and, therefore, subset B may very well include items other than A's. Therefore, this is a non sequitur.

The key is that the initial example is convoluted (in my opinion).


 * I believe the initial example is formulated according to the standard procedure on articles concerning logic. It is also quite clear and a much better general example of the subject than yours which is much more specific. There are more specific examples in the article. Of course, since you didn't sign your comment I don't know which version of the article you had before you so please do so in the future. Vadigor (talk) 19:20, 5 August 2008 (UTC)

Examples
Could someone please think of an example of non sequitur that isn't an undistributed middle? 64.90.198.6 00:27, 13 December 2006 (UTC)\

Wrong Fallacy?
''The article says:'

An example of affirming the consequent would be:

If I am a human (A) then I am a mammal. (B) I am a mammal. (B) Therefore, I am a human. (A)

This is a fallacy of affirming the consequent

Relation to Causation Article
I was just wondering whether this should be merged or linked with the page Correlation is not causation? DeathscytheH64 23:25, 8 May 2007 (UTC)

Ann Coulter
I believe this section should somehow include Ann Coulter, no explanation is necessary. Theonlysilentbob 18:22, 4 October 2007 (UTC)

Hair
"'If my hair looks nice, all people will love me.' However, there is no real connection between your hair and the love of all people."

I think that this is totally unsound. How does physical appearance not apply to the feelings of others towards the one possessing that appearance? —Preceding unsigned comment added by Hierophantasmagoria (talk • contribs) 07:38, 27 January 2008 (UTC)


 * It seems like you do not understand the nature of the non sequitur in question. While it is true that physical appearance 'may' influence others it most definitely will not make 'everyone' love the person. This is a non sequitur coupled with (or derived from) a faulthy generalization. Vadigor (talk) 20:49, 5 August 2008 (UTC)


 * Yes that is unsound. Thats why its a logical fallacy. — Preceding unsigned comment added by 75.167.99.93 (talk) 20:08, 18 September 2011 (UTC)

Discussion whether to merge the article "weasel word" with " non sequitur (logic)"
I disagree absolutely that "weasel word" be merged with the totally esoteric and abstruse article "non sequitur (logic)". We should accept that readers will not be looking for "non sequitur" but most certainly for "weasel word", because that is the usual expression. Dieter Simon (talk) 23:42, 1 August 2008 (UTC)

Agree with Dieter Simon that "weasel word" should not be merged with this topic ["non sequitur (logic)"]. I have seen no argument in favor of this original suggestion that endorses any direct commonality between the two phrases or their underlying logics.--Truce57 (talk) 17:53, 18 January 2009 (UTC)


 * It should not be merged. The subjects only have some overlap and neither is a subset of the other. Chillum  17:56, 18 January 2009 (UTC)

The articles should not be merged. I have tried to see a strong link between the two subjects, but from one to the other is a non sequitur. Sorry, couldn't resist. Centrepull (talk) —Preceding undated comment was added at 06:08, 22 January 2009 (UTC).

Unfortunately the above people don't seem to be able to read english..... "Generalizations and non sequitur statements" is the section which is being discussed here, not the whole article. I don't think they should be merged, as this section provides some background (wider reading as it were) to the topic. 86.26.232.254 (talk) 08:11, 22 May 2009 (UTC)

Rewrite
This article requires a fairly large rewrite I think, as it is now, it mostly explains the use of the term in formal logic, without making much reference to the use of the term in normal speech and reasoning. Distinguishing a Formal Logic and Common Use section would be more appropriate but I'm having trouble with rewording it properly to keep a proper first paragraph. Vadigor (talk) 19:25, 5 August 2008 (UTC)


 * I'm currently rewriting the article as per what I explained above. I have removed most of the examples given at the end of the article. These are not clear indications of non sequitur logic since only their premise is given. Furthermore I do not believe these should belong in this article. For reference here are the examples I removed:


 * "A growing body of evidence..." (Where is the raw data for your review?)
 * "Our product is so good, it was even given away in celebrity gift bags." (True, perhaps, but not relevant.)
 * "See why more of our trucks are sold in southern California than in any other part of the country." (Southern California is a big vehicle market.)
 * "Nobody else's product is better than ours." (They're all about the same.)
 * "Becoming involved with this problem would be beneficial to us." (In what way would it be beneficial?)
 * "People say..." (Which people? How do they know?)
 * "Critics claim..." (Which critics?)
 * "I heard that..." (Who told you? Is the source reliable?)
 * "There is evidence that..." (What evidence? Is the source reliable?)
 * "Experience shows that..." (Whose experience? What was the experience? How does it demonstrate this?)
 * "It has been mentioned that..." (Can these mentioners be trusted?)
 * "Popular wisdom has it that..." (Is popular wisdom a test of truth?)
 * "It is known that..." (By whom and what method is it known?)

Eminem is correct, thus there is no non-sequitur.

Q.E.D.

--FeralOink (talk) 23:15, 3 February 2013 (UTC)

Examples - normal speech
The "normal speech" section says non sequitur describes "a statement in which premise and conclusion are totally unrelated" (my emphasis), but in all of the examples the premise and conclusion are very obviously related: phones are related to image, pet food is related to dogs, and rain is related to sun. In the first example, the article correctly says that "there is no direct relation" between the two, but that is a very different thing to "totally unrelated". Examples of non sequiturs would be more in the line of "If you do not buy this type of pet food, the sun will not shine." Scolaire (talk) 18:01, 29 September 2011 (UTC)

My favorite: "Everything should be made as simple as possible, but not one bit simpler." --Albert Einstein --Anewcharliega (talk) 18:53, 22 September 2015 (UTC)

Pronunciation Guide
It would be nice if there was a phonetic spelling of the words in the header. — Preceding unsigned comment added by Vaccano (talk • contribs) 20:47, 20 December 2012 (UTC)

IF YOU HAVE TWO Non sequitur (logic)
IF YOU HAVE TWO Non sequitur (logic) WORDS OR PHASES OR SENTENCES OR ANY COMBINATION OF THESE. IN A ROW OR SENTENCE. THENCE, THEN YOU HAVE ? — Preceding unsigned comment added by 74.178.222.20 (talk) 06:27, 9 November 2013 (UTC)

Regarding 22:43, 26 June 2015‎ edit by McGeddon
The note states "That would still be "false"."

The premise of "not even wrong" is explicitly describing something as not-false. You are saying that something not-false is false. — Preceding unsigned comment added by 70.114.194.209 (talk) 00:27, 27 June 2015 (UTC)

Greetings, comrades.
Article needs to explain how it's pronounced.

--88.88.251.162 (talk) 13:26, 18 August 2016 (UTC)

Merge to Formal fallacy
The lead section states that non sequitur is a logical fallacy, which does not belong to any of the named subclasses of logical fallacies. This means that this article can only concern with a general description of logical fallacies. The entire section Logical constructions actually discusses the named subclasses of logical fallacies. Additionally, logical fallacy is a synonym for formal fallacy. Therefore I propose to merge this article to Formal fallacy. Petr Matas 15:33, 12 April 2018 (UTC)
 * ✅. Petr Matas 14:22, 2 May 2018 (UTC)