I have a question about the identity of a certain kind of fallacy, namely:
A = C
B = C
therefore A = C
Confusingly, I have read that the above syllogism is valid; and yet consider this argument I've heard recently:
Obama = Good speaker
Hitler = Good speaker
therefore Obama = Hitler
Clearly the latter is a fallacy.
So, I have two questions, really:
1) What is the name of this fallacy?
2) How can it be a fallacy if the first syllogism (A = C, B = C, therefore A = C), whose form it follows, is considered to be valid . . . or am I wrong about it being valid?
Well, yes and no. What you've got here is a tangle, just the sort of tangle that actually does lead to serious philosophical problems. You see, what you've got in the first place isn't exactly a syllogism. So, it's neither a valid nor an invalid syllogism. It looks a lot like the following syllogistic form (which is invalid): "All P are M. All S are M. Therefore, All S are P." You can see that this invalid by plugging in the following terms. "All Pigs are Mammals. All Siberian Huskies are Mammals. Therefore, all Siberian Huskies are Pigs." While the two premises are true, the conclusion is clearly false--and that doesn't happen in valid arguments. This invalid form doesn't have a specific name, really, but it does commit the fallacy of "undistributed middle." I think one reason you may have lost your way here is because you use equal signs in your presentation. If you intend to use the equal sign as short hand for the verb "to be" ("are") in the same what as I have used "to be" ("are") in my example,...