What Are The Names of These Logical Fallacies?

[HeyHomie]

On another message board I visit, someone started a thread based on a logical fallacy. I’m trying to point that out to him, but the name escapes me.

Here’s how it goes:

Che Guevara liked to wear ties. Republicans like to wear ties.
Che Guevara liked to invest in the stock market. Republicans like to invest in the stock market.
Che Guevara liked to play golf. Republicans like to play golf.

…ergo, Che Guevara was a Republican

I’ve also seen threads that go like this:

The person who came up with the idea you’re espousing was a VERY BAD PERSON. Therefore, the idea you’re espousing is very bad.

or, put another way:

The ancient cult of [insert god here] cremated their dead.
The ancient cult of [insert another god here] also cremated their dead.
The founders of our religion buried their dead.
…ergo, creation is an occultic practice.

Can anyone help me out with these?

Thanks.

[Tevildo]

The first and third are the fallacy of Undistributed Middle. It’s an invalid form of the Aristotelian syllogism:

Valid argument (Barbara):

1. All As are Bs
2. All Bs are Cs
   Conclusion:
3. Alll As are Cs.

B is the middle term in this syllogism. The invalid form is, as quoted:

1. All As are Bs
2. All Cs are Bs
   Conclusion:
3. All As are Cs.

The fallacy is called “undistributed middle” because the middle term, B, isn’t “distributed” across the class of C’s - “All Cs are Bs” doesn’t mean “All Bs are Cs”.

The second one is the Genetic Fallacy. It’s not strictly a logical fallacy, as it doesn’t involve invalid reasoning - it just involves introduction of irrelevant material to the argument.

[Valgard]

Here’s a listing of the various fallacies: http://www.nizkor.org/features/fallacies/

[chrisk]

I think the second one could also be considered an ad hominem fallacy. By attacking the author of the claim, it fallaciously attempts to disprove an idea.

[chrisk]

@Valgard

Here’s a listing of the various fallacies: http://www.nizkor.org/features/fallacies/

I don’t think that’s a complete listing… it doesn’t have the undistributed middle, which certainly seems like a good one.

Nice reference site on fallacies anyway.

[Tevildo]

There’s a good, comprehensive list at The Atheism Web - most of the examples are, understandably, invalid arguments for the existence of God, but that doesn’t make the fallacies any less general.

[Barely_Adequate]

Here’s another excellent resource: The Logical Fallacy Index

http://www.datanation.com/fallacies/index.htm

[Valgard]

@chrisk

I don’t think that’s a complete listing… it doesn’t have the undistributed middle, which certainly seems like a good one.

Nice reference site on fallacies anyway.

[Dr. McCoy voice ON]

I’m an IT specialist, not a logician!

[Dr. McCoy voice OFF]

[Chronos]

There’s a good, comprehensive list at The Atheism Web - most of the examples are, understandably, invalid arguments for the existence of God, but that doesn’t make the fallacies any less general.

Well, if atheists think they’re fallacies, then they obviously must be valid arguments, since God exists.

ducking and running

[pravnik]

I’m not so sure the first would be fallacy of the undistributed middle; it would be if it were a deductive argument written as categorical syllogism, but it appears to be written as an inductive argument. I would be inclined to label it a hasty generalization and a fallacy of relevance. Three minor factors in common aren’t enough to establish the connection, and wearing ties, investing, and playing golf are not relevant to political views. I would agree that the second is a genetic fallacy and an ad hominem. I don’t think I understand the third one.

[Tevildo]

[QUOTE=pravnik]
I’m not so sure the first would be fallacy of the undistributed middle; it would be if it were a deductive argument written as categorical syllogism, but it appears to be written as an inductive argument.

[quote]

1. All persons called Che Guevarra are tie-wearers.
2. All Republicans are tie-wearers.
3. All persons called Che Guevarra are Republicans.

Absolutely classic Undistributed Middle. More seriously, your concern shows that an inductive argument can never be proved within syllogistic logic.

I don’t think I understand the third one.

True, it’s the most complex of the three. It’s definitely an invalid syllogism of some sort:

1. Some evil religions are practitioners of cremation.
2. All evil religions are evil.
3. All practitioners of cremation are evil.

But I don’t know the precise name for that reasoning.

[pravnik]

@Tevildo

1. All persons called Che Guevarra are tie-wearers.
2. All Republicans are tie-wearers.
3. All persons called Che Guevarra are Republicans.

Absolutely classic Undistributed Middle. More seriously, your concern shows that an inductive argument can never be proved within syllogistic logic.

Okay, written that way, definitely syllogistic and fallacy of the undistributed middle. I guess you can view it as three invalid syllogisms in a row or one weak inductive argument viewed as a whole.

@Tevildo

True, it’s the most complex of the three. It’s definitely an invalid syllogism of some sort:

1. Some evil religions are practitioners of cremation.
2. All evil religions are evil.
3. All practitioners of cremation are evil.

But I don’t know the precise name for that reasoning.

Heh…I just realized the reason I didn’t understand it:

The ancient cult of [insert god here] cremated their dead.
The ancient cult of [insert another god here] also cremated their dead.
The founders of our religion buried their dead.
…ergo, creation is an occultic practice.

I was thinking “what the heck does that have to do with creationism?”

[chrisk]

@pravnik

Okay, written that way, definitely syllogistic and fallacy of the undistributed middle. I guess you can view it as three invalid syllogisms in a row or one weak inductive argument viewed as a whole.

Umm… how would it comprise three syllogisms, valid or not? A single statement of the form ‘a relates to b’ is not a syllogism. You need three of them.

A relates to B
B relates to C
therefore, A relates to C.

Some of them can be flipped so as to more easily phrase the relationship. Which relationships are used will determine if the syllogism is valid or not… do I have that right??

[Rick]

[hijack] If you want to hear a whole series of very funny versions of these, get a copy of Richard Jenni’s Greatest Bits CD. Funy funny stuff
[/hijack]

[Tevildo]

@chrisk

Umm… how would it comprise three syllogisms, valid or not?

All persons called Che Guevarra are tie-wearers.

All persons called Che Guevarra are stock-market investors.

All persons called Che Guevarra are golfers.

[pravnik]

@chrisk

Umm… how would it comprise three syllogisms, valid or not? A single statement of the form ‘a relates to b’ is not a syllogism. You need three of them.

A relates to B
B relates to C
therefore, A relates to C.

They’re enthymemes. An enthymeme is a syllogism with a proposition missing as self-evident. The typical enthymeme is a syllogism with one of the premises missing, but a missing conclusion qualifies as well, depending on who you ask. Most people making arguments in rhetoric use enthymemes instead of speaking in whole syllogisms. The whole arguments would be:

1. All persons who are Che Guevara are persons who like to wear ties.

2. All Republicans are persons who like to wear ties.

3. All persons who are Che Guevara are Republicans.

4. All persons who are Che Guevara are persons who like to invest in the stock market.

5. All Republicans are persons who who like to invest in the stock market

6. All persons who are Che Guevara are Republicans.

7. All persons who are Che Guevara are persons who like to play golf.

8. All Republicans are persons who like to play golf.

9. All persons who are Che Guevara are Republicans.

Three invalid syllogisms. The whole statement can be characterized as an inductive argument as well:

Che Guevara has characterisistic A in common with Republicans.
Che Guevara has characterisistic B in common with Republicans.
Che Guevara has characterisistic C in common with Republicans.
Therefore, Che Guevara is a Republican.

[Tevildo]

@Tevildo

True, it’s the most complex of the three. It’s definitely an invalid syllogism of some sort:

1. Some evil religions are practitioners of cremation.
2. All evil religions are evil.
3. All practitioners of cremation are evil.

But I don’t know the precise name for that reasoning.

The books say that it’s Illicit Minor. Thanks.

[Crowbar_of_Irony_3]

@pravnik

They’re enthymemes. An enthymeme is a syllogism with a proposition missing as self-evident. The typical enthymeme is a syllogism with one of the premises missing, but a missing conclusion qualifies as well, depending on who you ask. Most people making arguments in rhetoric use enthymemes instead of speaking in whole syllogisms. The whole arguments would be:

1. All persons who are Che Guevara are persons who like to wear ties.
2. All Republicans are persons who like to wear ties.
3. All persons who are Che Guevara are Republicans.

As I understand it, it seems to be a case of converse error.

By rules of logic, if x implies y, it doesn’t means that y impliesx. I could rework the three statements are:

R(x) - x is a Republician
T(x) - x likes to wear tie
C(x) - x is Che

1. For all person x, if R(x) then T(x)
2. For all person x, if C(x) then T(x)

To prove: For all person X, if C(x) then R(x), which is quite impossible

3. Che likes to wear tie could be represented as: C(c)
4. C(c) then T(c) : Universal instantiation, which means if c is Che, then c likes tie
5. R(c) then T(c) : Universal instantiation, which means if c is a Republician, then c likes tie.
6. T(x) then R(x) : Convese error - Anyone who likes tie is a Republician
7. C(c) then T(c) then R(x): Law of syllogism

The error starts in step 6…And if there’s fancy name for it, then I only know it as Converse Error…