Logical Fallacies

Logical Fallacies

December 1, 2005

A logical fallacy is an error in logical which is independent of the truth of the premises. It is a flaw in the structure of an argument as opposed to an error in its premises. When there is a fallacy in an argument it is said to be invalid. The presence of a logical fallacy in an argument does not necessarily imply anything about the argument's premises or its conclusion. Both may actually be true, but the argument is still invalid because the conclusion does not follow from the premises using the inference principles of the argument. By extension, an argument can have a logical fallacy even if the argument is not a purely logical one; for instance an argument that incorrectly applies principles of probability or causality can be said to have a logical fallacy.

Recognizing fallacies in practical arguments may be difficult since arguments are often structured using rhetorical patterns that obscure the logical connections between assertions. Having the capability of recognizing logical fallacies in arguments will hopefully reduce the likelihood of such an occurrence.

1) Argumentum ad hominem (Argument against the person)

The Latin name of this fallacy means "argument against the person." In this type of argument the arguer is making a personal attack on the opponent in order to persuade the listener to reject the opponent's thesis. The personal attack can take the form of an abusive attack on the character of the opponent, such as that he can't control his emotions or desires, (an abusive ad hominem), or an attack that presents some negative circumstances regarding the opponent, such as that he did not attend the best law school, (a circumstantial ad hominem). Since such matters are usually completely irrelevant to the conclusion, the argument is a non sequitur.

This argument has the structure:

1. Person A proposes X.

2. Person A has some characteristics F.

3. The audience does not approve of F.

[This causes the audience to have a general negative attitude towards person A, including A's proposal X.]

4. So, proposal X is not correct.

Here too, the argument is doubly erroneous. First of all, disapproval of some characteristic F of a person is not a rational reason to have a general negative attitude towards that person. Secondly, even when there is a general negative attitude towards a person, that fact has no connection to the correctness of a given view, even if that view happens to be proposed by that person.

Ad hominem fallacies are very common in political fights, where candidates attack each other's character, rather than their platform or accomplishments. Sometimes, these types of arguments make sense -- If a candidate has a long record of reneging on promises, it is reasonable to argue that future promises may not be kept. However, it is not valid to argue that a candidate's broken promises in the past indicate that his or her position on welfare reform is untenable. The good example was in the last presidential election where the campaign strategy was accusing opponent of flip-flopping.

2) False Dilemma

The false dilemma, or false dichotomy, is a fallacy that presents two issues as if they are the only possible choices in a given situation. The rejection of one choice, in such a situation, requires the adoption of the second alternative. False dichotomies should be distinguished from true dichotomies. Sometimes, there really are only two choices: everything in the world is either a dog or a non-dog, but everything isn't either a dog or a cat. In most, but not all, situations, there are middle grounds or other options that make it irresponsible to force a choice between two alternatives.

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