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.
The first and third are the fallacy of Undistributed Middle. It’s an invalid form of the Aristotelian syllogism:
Valid argument (Barbara):
All As are Bs
All Bs are Cs
Conclusion:
Alll As are Cs.
B is the middle term in this syllogism. The invalid form is, as quoted:
All As are Bs
All Cs are Bs
Conclusion:
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.
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.
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.
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.
[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]
All persons called Che Guevarra are tie-wearers.
All Republicans are tie-wearers.
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.
True, it’s the most complex of the three. It’s definitely an invalid syllogism of some sort:
Some evil religions are practitioners of cremation.
All evil religions are evil.
All practitioners of cremation are evil.
But I don’t know the precise name for that reasoning.
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.
Heh…I just realized the reason I didn’t understand it:
I was thinking “what the heck does that have to do with creationism?”
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??
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[/hijack]
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:
All persons who are Che Guevara are persons who like to wear ties.
All Republicans are persons who like to wear ties.
All persons who are Che Guevara are Republicans.
All persons who are Che Guevara are persons who like to invest in the stock market.
All Republicans are persons who who like to invest in the stock market
All persons who are Che Guevara are Republicans.
All persons who are Che Guevara are persons who like to play golf.
All Republicans are persons who like to play golf.
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.