Logical Fallacies

Definition of terms and explanation of concepts

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McCulloch
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Logical Fallacies

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Post by McCulloch »

Imagine my horror when I went to one of my favourite pages with a handy list of logical fallacies to get a 404 page not found error. So as a public service, I will list with examples a few logical fallacies. I am deeply indebted to Logic & Fallacies at infidels.org, Table of Fallacies by Bruce Thompson, Stephen's Guide to the Logical Fallacies by Stephen Downes and Logical Fallacies and the Art of Debate by Glen Whitman. The Nizkor Project has another excellent list of logical fallacies. Here are some more reference pages for logical fallacies, complements of ST88:
Logical Fallacies by Michael Wong and How to Answer Questions (Without Offending People) - a Mormon source (anyone see the ad hom?)
A few things to note.
  • Just because the logic is false, the assertion may still be true.
  • Just because the logic is correct, the assertion may be false. The premises may be false.
I will try to include blatant examples to illustrate each fallacy. I will probably fail at my attempts to provide balanced examples. Please forgive me.
Edited to add Nizkor Project and links from ST88 (thanks)
Last edited by McCulloch on Fri Nov 04, 2005 9:33 am, edited 1 time in total.
Examine everything carefully; hold fast to that which is good.
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Cathar1950
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Post #11

Post by Cathar1950 »

McCulloch wrote:The fallacy fallacy is where you conclude that a particular assertion is false simply because the person making the assertion has committed logical fallacies in reaching his conclusion. In pointing out that someone has made logical fallacies, all one can do is show that their conclusions are not valid based on the evidence and reasoning so far provided not that their conclusions are necessarily false.
Sometimes they are just so obvious it is fun just to name them and point them out.
I agree there wouldn't be anything wrong with them if it were not that they lead to illogical and false conclusions.
Why can't you divide by zero?
Because any and every answers is right and and could be wrong.

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Argumentum ad populum

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Post by McCulloch »

Argumentum ad populum

An argumentum ad populum (Latin: "appeal to the people"), in logic, is a fallacious argument that concludes a proposition to be true because many or all people believe it; it alleges that "If many believe so, it is so." In ethics this argument is stated, "If many find it acceptable, it is acceptable."

This type of argument is known by several names[1], including appeal to the masses, appeal to belief, appeal to the majority, appeal to the people, argument by consensus, authority of the many, and bandwagon fallacy, and in Latin by the names argumentum ad populum ("appeal to the people"), argumentum ad numerum ("appeal to the number"), and consensus gentium ("agreement of the clans"). It is also the basis of a number of social phenomena, including communal reinforcement and the bandwagon effect, and of the Chinese proverb "three men make a tiger".

Source: Wikipedia

Variations:
  1. "Snob Appeal": the fallacy of attempting to prove a conclusion by appealing to what an elite or a select few (but not necessarily an authority) in a society thinks or believes.
  2. "Bandwagon": the fallacy of attempting to prove a conclusion on the grounds that all or most people think or believe it is true.
See also:
http://nizkor.org/features/fallacies/ap ... arity.html
http://atheism.about.com/od/logicalfall ... umbers.htm
Examine everything carefully; hold fast to that which is good.
First Epistle to the Church of the Thessalonians
The truth will make you free.
Gospel of John

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SonicBarnacle
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Post #13

Post by SonicBarnacle »

I like the taxonomy at fallacyfiles.org.
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McCulloch

Post #14

Post by Kadmon »

McCulloch wrote:The fallacy fallacy is where you conclude that a particular assertion is false simply because the person making the assertion has committed logical fallacies in reaching his conclusion. In pointing out that someone has made logical fallacies, all one can do is show that their conclusions are not valid based on the evidence and reasoning so far provided not that their conclusions are necessarily false.

Hummmmmmmmm So This Is Where You Gotten Your Attributes From O:)

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Re:

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Post by TRANSPONDER »

McCulloch wrote: Sun Apr 08, 2007 10:43 pm The fallacy fallacy is where you conclude that a particular assertion is false simply because the person making the assertion has committed logical fallacies in reaching his conclusion. In pointing out that someone has made logical fallacies, all one can do is show that their conclusions are not valid based on the evidence and reasoning so far provided not that their conclusions are necessarily false.
That is true. However the logic would deman that their assertion has to be regarded as not validated because their logic was wrong. It still has to be validated with good evidence or valid logic.

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Re: Logical Fallacies

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Post by TRANSPONDER »

What is the You Too fallacy?
"Tu quoque" means "you too," and consists of responding to allegations of wrong doing by saying, in essence, "you do the same thing." That response may be true, but it doesn't deny or explain away the alleged wrongdoing. Tu quoque is also known as the "you too" fallacy, and the "two wrongs make a right" fallacy.


The fallacy here is that two wrongs do not make a right, or rather more that someone who took a person to court for stealing his money could not be attacked on the grounds that he once stole from someone else. That makes no difference to the actual case.

However, I have long felt that there is an exception to that rule which is when one side is trying to claim a moral superiority. If an inventor puts a machine on the market and another mechanic points out that it doesn't work, it is irrelevant for the other one to say 'You can't talk - you invented a machine that didn't work, too'. That makes no difference to the fact that His machine doesn't work.

However, if the other person says 'I'm a better inventor than you because your machine doesn't work', this claim to be 'better' can be refuted by pointing out that his machine didn't work, either. Thus a claim to moral superiority CAN be refuted by a Tuo Quoque.

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Re: Logical Fallacies

Post #17

Post by TRANSPONDER »

The black swan fallacy is the tendency of people to ignore evidence that contradicts their beliefs and assumptions. This fallacy can also refer to the tendency to believe that things they've never witnessed don't exist.

I find this one very interesting. Not least because the black swan fallacy sometimes seems to be reversed - 'Just because you've never sen a black swan doesn't mean there aren't any' or 'Well, it was claimed that all swans were white, but all the time the Fact was that there were black swans, but they didn't know it'.

This has all kinds of ramifications and can be used (and mis -used) in various ways. It's why I reject the 'miracles don't happen' argument for rejecting the resurrection. Black swans (miracles) are dubious until they are proven. The resurrection is to be doubted until it is verified (by the reliable report of the disciples)(1).

A favourite fallacious use of this is 'The skeptics denied powered flight'. The implication being this argument:

"When the Wright brothers made the first flight, these so -called scientists refused to believe that it was true. But they were wrong and they looked like fools. Now they deny the existence of God and the will look like fools about that, too. You don't want to be a fool do you? So you'd better believe in God'.

I hardly need point out the wonky chain of reasoning there, but the way that the fallacy itself can become the fallacy is to misunderstand agnosticism and the burden of proof.

It was wrong (as it turned out) to deny that there 'were' (could exist) any black swans. But it was perfectly valid to say that there was no good evidence that black swans existed until it was proven that they did.

Thus is was valid for the Skeptics to doubt powered flight until it was validated. Once it was 'proven' of course those who doubted it might be presented as fools, but their request for validation was correct. Consider the claim of cold fusion back in the day. If they'd just accepted it as a claim, they'd have had egg all over their faces later on. It was necessary that the claim be doubted until verified.

Thus agnosticism (not knowing until we do know) is logically correct until the evidence is verified as compelling. The burden of proof is on the one making the claim.
(1) So the logical question is not 'do miracles happen?' but 'is the report reliable?'

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