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Explanation of Principles |
I have tried to organize the fallacies on this website according to what I consider to be the actual structure of reasoning, not just according to arbitrary similarities. A warning to visitors is in order. This set of principles is rather idiosyncratic. Other logic teachers use other principles (or no principles at all). To justify my eccentricities, let me note that my approach to fallacies has been significantly influenced by the logical writings of Charles S. Peirce (in ways that will be obvious to those familiar with his work and probably won't matter to those who aren't).
This classification scheme is based on three principles:
| 1. Classification of fallacies should be based on where the fallacy occurs. | |||||||||
A fallacious argument contains an error of some kind. We can classify
fallacies based on where this error occurs. Fallacies are traditionally divided into two
groups, formal fallacies and informal fallacies. Formal
fallacies are fallacious because there is an error in their form; informal fallacies are
fallacious because they have a false premiss. With modifications, I accept this idea. I
think there are two basic types of fallacies:
Fallacies of Soundness may be further sub-divided according to which of its
premisses is false. To simplify (perhaps, oversimplify) this idea, we will assume that all
reasoning follows the basic pattern of the syllogism. A syllogism is an argument
with two premisses leading to a conclusion. Each proposition in the argument has two
terms, and, in the course of the argument, each term occurs twice, but never twice in the
same proposition. The classic example of a syllogism is:
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The subject of the conclusion (Socrates) is called the minor term; the
predicate of the conclusion (mortal) is called the major term. Hence the premiss in which
the major term occurs (All men are mortal) is called the major premiss; the premiss in
which the minor term occurs (Socrates is a man) is called the minor premiss. The basic
idea is this: fallacies of soundness can be classifed according to whether it is the
major premiss or the minor premiss that is false. So Fallacies of Soundness may be
divided into three categories:
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| 2. There are three kinds of reasoning, not just two. | |||||
Using the syllogistic model, we can see that there are actually three
types of reasoning. Most logicians recognize only two. It was the great pragmatic
philosopher Charles S. Peirce who first identified Retroduction as a third type of
argument, not just a species of Induction. He used the structure of the syllogism to
explain his division. (For details, click on the links below.)
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| 3. All fallacious reasoning is formally valid (for its type). | ||
| We must assume that not all of the premisses of an argument are
necessarily stated. Often people offer arguments without stating all of the premisses that
would be needed to make the argument formally valid. Usually they do so because the
unstated premisses are obvious, and stating them would be boring and pointless.
For example, someone who argued "Socrates is mortal, since all men are mortal,"
would not be accused of reasoning in an invalid manner. He has merely treated the missing
premiss "Socrates is a man," as too obvious to require explicit statement--and
he is surely not wrong to do so. However, if we are to treat incomplete
arguments as valid, the critic of the
argument must be responsible for unstated as well as stated premisses. Yet,
any argument can be rendered valid by the addition of some premisses or
other, provided we do not insist that those premisses be true.* This puts
the critic in the position of being able to assume that any bad argument is
valid. The object of critique is, then, not to judge the validity of an
argument, but only to expose the false or circular premisses that render the
argument bad even when (or perhaps especially when) those premisses
have been left unstated. An argument is fallacious when, in spite of its formal validity, there is good reason that it should fail to persuade us. Notice that even Fallacies of Circularity are formally valid, although their error is in their form. |
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What about the classical formal fallacies? Click on the link for a discussion.
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* This statement can be established through a rather trivial proof. Given any premiss, p, and any conclusion, q, a valid argument can be constructed with the addition of the premiss, 'If p then q'. Alternatively, we could construct a valid argument by adding q as a premiss, rendering the argument circular, but valid.