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A Project of The Annenberg Public Policy Center

On Logical Fallacies

We’re always pleased when our readers write to us with questions or comments that really make us think. Here, for example, is reader K.S., who writes:

Perhaps it was intended facetiously, if so I apologize for this “correction.” However, in your piece on ACORN you concluded with the following statement, “We’re accustomed to seeing logical fallacies in political arguments. But working two of them into a single argument is unusually bad logic.”

All fallacies are errors in logic, ergo any fallacy is a “logical” fallacy. Working one of them into an argument is, by definition “bad logic” and working two of them in is just worse logic. The nit-pick police have done their job. I do appreciate the write up though.

K.S. is referring to our recent Ask FactCheck item addressing whether the stimulus bill provides $5.2 billion in funding for ACORN (it doesn’t, but there are funds for which ACORN could compete — against hundreds of other groups — should it choose to do so.) She raises a good question here: Is “logical fallacy” redundant?

The short answer is, we don’t think so.

“Fallacy” as the word is commonly used has two different meanings, the most common of which is to use the word as a synonym for “false” or “incorrect.” And, of course, “fallacy” can also be used to describe an argument that relies upon faulty reasoning. We use “logical fallacy” to clarify that we mean the second rather than the first sense of “fallacy.”

There is also a slightly longer and more technical answer to K.S.’s question, so if you’re interested in that sort of thing, please join us below the fold.

See, there are different kinds of errors in reasoning. Some kinds involve a lack of fit between premises and conclusions. Here’s an example we’ve used before:

All clouds are white.
All sheep are white.
Therefore all clouds are sheep.

That’s our old friend, the fallacy of the undistributed middle. And it’s an error in logic; the conclusion simply does not follow logically from the premises. But not all fallacies are like that. Consider this one:

Capitalism is the best economic system because without capitalism the free market wouldn’t be possible.

This isn’t a particularly convincing argument. Unless of course you’re already convinced that capitalism is the best economic system. There’s nothing wrong with the logic of this claim, but that’s because the conclusion just restates the premise. Philosophers call this the fallacy of begging the question (really pretentious philosophers call it petitio principii). But it’s not a fallacy because it gets the logic wrong. After all, a claim will always logically entail itself. The fallacy part lies in thinking that the premise provides any particular sort of reason for believing the conclusion. There’s an error in reasoning going on, but that error is not, strictly speaking, an error in logic.

So strictly speaking, not all fallacies are errors in logic, per se. But they are all errors in reasoning. And while we agree with our reader that having any fallacy at all is bad logic, we’ve grown so accustomed to seeing them that it we’re only really surprised when we get two (or more) in a single argument.

Want to weigh in on fallacies? Drop us a line and put my name in the subject line.