Talk:Logical fallacy

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Manufacturing facts from a theory

" the source of many controversies in modern astronomy, some of them strikingly bitter"

Umm...really? Such as?

In any case, this is pretty weak. The entry's written broadly enough to cover basically all scientific inference. Strictly speaking invalid from a deductive point of view, but still. Tsumetai 10:04, 6 March 2007 (EST)

You asked, "Such as?" And I'll give you some examples. Start with the Oort cloud, the so-called "cloud of comets" where comets reside until something knocks them into the near solar system. Why do we hear of the Oort cloud?
  1. Comets lose their brilliance and become invisible to the naked eye after 100 near-sun passes.
  2. A large number of comets are "short period" comets that are still brilliant. (Example: Comet Halley, which makes a pass ever 76 years, and heralded the birth and death of Samuel L. Clemens)
  3. Therefore, the solar system can be no older than 7600 years.
  4. But this is "impossible" since radiometric dating "says" that the earth itself is 4.6 billion years old.
  5. Therefore, comets reside in a "cloud of comets" in the outer reaches of the solar system, and do not actually start making long, thin orbits of the sun until some passing asteroid perturbs their orbits and knocks them "down."
The Oort cloud is, therefore, a fact manufactured to support the theory of an age for the solar system measurable in billions of years.
Back to Sir Isaac Newton: He made a definite prediction about the strength of gravity and the orbits of the planets. But one planet did not cooperate: Mercury. When it reaches perihelion, it deviates significantly from a path that a strict Newtonian calculation would predict.
  1. Newton's Law of Gravitation predicts that Mercury should pass in a certain way.
  2. Mercury deviates from that path.
  3. Therefore the solar system contains another planet (named "Vulcan") inside of Mercury.
Centuries later, Albert Einstein issued a correction that explained Mercury's orbit without resort to any "new innermost planet."
The inferred planet Vulcan was, therefore, a "fact" manufactured to support a theory that was clearly inadequate. Astronomers insisted that this planet must exist, even though no man had ever seen it, until Einstein finally solved the riddle.
That's not such a bitter example. The bitter examples today involve anomalies in all the planets--things that no theory of "spontaneous generation" of planets can possibly explain. So in each and every case, astronomers manufacture an historical "fact"--that a large asteroid--not in evidence today--collided with the planet and brought about the anomaly.
This sort of thing stands in violation of Occam's razor, which states that one must not multiply unsupported inferences without sufficient reason.--TerryH 12:55, 6 March 2007 (EST)
No, you are confusing predicting things and manufacturing facts. Vulcan was a prediction of the prevailing theory at the time. That's distinct. JoshuaZ 13:02, 6 March 2007 (EST)
Indeed; as I suspected, this really is broad enough to catch any scientific inference one doesn't like.
Incidentally, as far as Occam goes, Vulcan was a considerably better hypothesis than some mysterious modification to Newtonian gravity, at least when it was first proposed. Tsumetai 15:50, 6 March 2007 (EST)


Newton's laws are not an example of an overgeneralization, but an example of an inferrence that didn't generalize as much and so shouldn't be in that set. The argument from authority section also misses that experts are only relevant if they have access to more resources of some form not accesible to the people in question (although strictly speaking, from a formal logical perspective, such an argument is never valid- but we seem to be not distinguishing between formal and informal logic here). JoshuaZ 10:36, 6 March 2007 (EST)


I would like to do a rewrite of this article. Does anyone object to me recategorizing the fallacies? If they are in some order now I can't really tell what it is. HelpJazz 17:25, 27 February 2008 (EST)

Seems nobody objects, so here goes nothing. On problem I see immediately is that editing is going to turn off soon. A longer-term problem is that there are many links to the sections, so if I change the sections I will have to change all the pages that link that way. We will see. I'll start with the introduction. HelpJazz 00:35, 21 March 2008 (EDT)
Alright, all done. To see my individual edits, check out the history here (look between March 21st and March 27th).
As I was going through my rewrite, I noticed that "Your theory does not work under my theory, so your theory must be wrong" is only found on CreationWiki. It probably has a different name in other logical texts, but I don't know what it is.
Additionally, I deleted the following section (which has been commented out to keep this page clean:
<Thar be text hidin' here>
There were a lot of problems, starting with the first sentence "Today, logic is offered as an elective in college, not as a requirement." This is clearly not true at every college or for every major (Philo majors?). It is riddled with problems (ad hominem is closely related to non sequiter? Eeeeeeeeh sort of, kind of, in a general, round-about way) and the rest isn't really related to logic as much as it is to teaching in colleges. That being said, it can probably be put back in if someone wants to, but I would argue that it needs work. 00:00, 28 March 2008 (EDT)

Section Removed

I removed "Tautology" from the list, because it is not a type of fallacy. Tautologies are statements of things which are true by definition. While they do not amount to an argument in themselves, they are nevertheless quite useful in forming arguments. Eoinc 18:35, 7 May 2008 (EDT)

And I just put that right back. The problem is that people have used tautology as an argument, and also have tried to prove their definitions by assertion. In writing the above you have just defended proof by assertion as a legitimate form of argument. That will not stand.--TerryHTalk 18:39, 7 May 2008 (EDT)
My understanding of a tautology is that it states the obvious out of formal necessity, usually as a prelude to the real argument. Things like "all triangles have three sides". I must be missing something here: can you give an example of an argument which is really a statement of a tautology? Eoinc 18:58, 7 May 2008 (EDT)
What you seem to think a tautology is, is actually an axiom. An axiom (from the Greek axios worthy, deserving) is something that all sides can agree upon. It is also something that deserves to have all sides agree upon it.
A fallacious tautology is either a redundancy (a statement of the obvious in a manner suggesting that another case could obtain that would violate the definition) or an attempt to assert a definition that not all sides can agree upon. The way one does this is usually to couch a definition in a manner that tries to make it more than it actually is. I've seen it used to mask proof by assertion, and also circular reasoning, another common fallacy.--TerryHTalk 21:00, 7 May 2008 (EDT)

Genetic Fallacy

The page claims that "The genetic fallacy does not apply to arguments against a theory that caused a true believer to commit atrocities in reliance on the theory", but this is entirely incorrect. Regardless of whether or not Hitler used the theory of ballistics to bomb London (the example given), the theory of ballistics could still be true or false. Regard the example given:

  • Hitler and his top aides believed in the theory of ballistics
  • Hitler and his top aides relied on the theory of ballistics to bomb London
  • Therefore, the theory of ballistics is likely wrong

This is a logical fallacy because it presents no evidence for its conclusion; it merely appeals to the consequences of belief in the theory of ballistics. The theory of ballistics might still be true, even if used to justify horrible atrocities. I think whomever said that "The genetic fallacy does not apply to arguments against a theory that caused a true believer to commit atrocities in reliance on the theory" is confusing an ideology with a theory. Ideologies can be 'wrong' in that we find them objectionable, but they cannot be factually incorrect because they're opinions. Scientific theories like the theories of ballistics or gravity cannot be 'wrong' solely because we find them objectionable, but they can be factually wrong. So yes, the genetic fallacy does apply, even when used to justify horrible atrocities. Logical fallacies have no exceptions - every logical fallacy is a logical fallacy. I don't want to change it because the founder of Conservapedia is the one who made up this excuse.

EDIT: It's even in the wrong section; the argument should be under the "Ad hominem abusive" section as an example, since it bases its conclusion that the theory of ballistics is wrong on the fact that Hitler was a war criminal, even though the fact that Hitler was a war criminal has nothing to do with the theory of ballistics.

Replace "ballistics" with "evolution" as appropriate to answer previous edits of this page. TFWilliams 14:08, 21 June 2009 (EDT)