Posted on 12/30/2003 11:34:11 AM PST by general_re
The example I still remember from a long-ago logic course is this:
1. If it rains, the streets will be wet.
2. The streets are wet.
3. Therefore it must have rained.
Your're probably right; if recollection serves, the "No True Scotsman" is actually a special case -- a an example of two types of fallacy being committed at the same time. I think comes down to "equivocation" and "begging the question" at the same time. The equivocation involves narrowing the definition [of a "true Scotsman"] as needed to avoid refutation, and the begging of the question is used to justify it.
Moving along, I've noticed that your wonderful series on logical fallacies isn't generating the sort of enthusiastic response it deserves. In order to rectify this, I propose the following: for each fallacy type, participants should provide actual examples culled from the archives of FR, as originally posted by, ummmmm...... let's just say "FReepers-no-longer-in-residence." THe Freeper posting the best example of a given fallacy will win a prize, say a one week stay on a deserted island with those hilarious and fun-loving former Freepers "ALS" and "Gore3000." The second place prize is a TWO weeks on the island with them......
That should liven things up a bit....
P1: If it rains, the streets will be wet.
P2: It did not rain.
C1: Therefore, the streets are not wet.
or:
If p, then q.
~p.
Therefore, ~q.
1. All communists are atheists.This, in various clumsy versions, was used by virtually all the now-gone creationists. Not only is the structure of the argument fallacious, but the premise is false.
2. Darwin was an atheist.
3. Ergo ...
Kewl - you keep giving me opportunities to introduce new stuff ;)
As you say, the structure of such an argument is incorrect, which makes the basic logical error in this argument a formal error, as opposed to the informal errors that this series has been devoted to thus far. Essentially, the argument is this:
P1: All communists are atheists.
P2: Darwin was an atheist. (effectively equivalent to the universal affirmative proposition that "All men named Charles Darwin are atheists", or "All 'Darwins' are atheists")
C1: Therefore, Darwin was a communist.
Or some such.
A term in a syllogism is said to be "distributed" when the proposition refers to all members of the class designated by that term. And in a standard syllogism, the middle term (in this case, "atheists") must be distributed in at least one of the premises. But the middle term is undistributed in both premises - no claims about all the members of the class "atheists" are advanced - and hence the syllogism is invalid on its face. Not surprisingly, this formal error is known as the fallacy of the undistributed middle. The fact that the second premise is known to be false is merely the icing on the fallacy cake, so to speak.
P1: All men named Charles Darwin are atheists.
P2: All atheists are communists.
C1: Therefore, all men named Charles Darwin are communists.
Notice that the middle term, "atheists", is now properly distributed, by virtue of the fact that the second premise refers to all members of the class. However, while the logic is now valid, it is still unsound, insofar as the premises are known to be false.
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