The Logical fallacy reference article from the English Wikipedia on 24-Apr-2004
(provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Logical fallacy

A logical fallacy is an error in logical argument or reasoning which is independent of the truth of the premises. It is a mistake in the way that the propositions or statements in an argument are logically related. When there is a fallacy in an argument it is said to be invalid. That is, the conclusion does not logically follow from the premises provided to support it. This sort of mistake does not mean that the statements made or the conclusion reached are necessarily true or false. Both conclusion and premises may actually be true, but the argument is still invalid because the conclusion does not follow from the premises presented.

Arguments intended to persuade may be convincing to many listeners despite fallacious reasoning. The truth of the premises may even significantly increase the probability of the truth of the conclusion. But such arguments are nonetheless flawed. Recognizing fallacies is often difficult, but it is important to be able to do so. A tempting conclusion is not more likely to be true because it is supported by a fallacious argument. Detecting and avoiding fallacious reasoning will at least prevent adoption of some erroneous conclusions.

Table of contents
1 A few examples
2 A list of fallacies
3 See also
4 External links

A few examples

Here is an example of a fallacious argument: >>

Here is an example of a fallacious argument:
James wants to prove that "all killing is wrong", so James argues:

  1. If one should not do X, all X is wrong. (X can be any action.)
  2. One should not kill.
  3. Therefore, all killing is wrong.

James has committed the logical fallacy of begging the question. In the argument he says that one should not kill and presents the statement with no qualifiers. But to prove that, or at least support it, he would have to prove or support that all killing is wrong — which is just what he is trying to argue. A supporter of the death penalty might think that some killing is fine, for example as punishment for particularly heinous crimes. James's argument presupposes its conclusion: one of the premises assumes that the conclusion is true. An argument that begs the question should not convince anyone. It is fallacious.

<<

More formally, the logical steps of James's modus ponens are:

  1. For any action X: If one should not X, all X-ing is wrong.
  2. "kill" is a valid replacement for action X.
  3. Therefore, if one should not kill, all killing is wrong.
(the "conditional claim" could be seen as another wording for the golden rule) and
  1. If one should not kill, all killing is wrong.
  2. One should not kill.
  3. Therefore, all killing is wrong.

Both of the applications are logical. It is not incumbent upon James to prove that "one should not kill" has to be true under all circumstances; the generalized version (the "conditional claim") does not contain that, the specialized version (the "antecedent") does not need to include it either. The above attempt to disprove James's logic is basically denying the antecedent and actually proving in a modus ponens:
  1. Accepting both of James's premises would conclude that all killing is wrong.
  2. A supporter of the death penalty might think that some killing is fine.
  3. Therefore, a supporter of the death penalty cannot accept James's premises.
and in a reductio ad absurdum:
  1. We assume: "For any action X: If one should not X, all X-ing is wrong."
  2. There exists at least one action X ("kill"), where: One should not X, but there exist cases where X-ing is right (or, more correct: right considered by some people).
  3. Therefore, "For any action X: If one should not X, all X-ing is wrong." is not true.

Here is another example of a logical fallacy. Suppose Barbara argues:

  1. Andre is a good tennis player.
  2. Therefore, Andre is 'good' — a morally good person.

Here the problem is that the word "good" has different meanings, which is to say that it is an ambiguous word. In the premise, Barbara says that Andre is good at some particular activity, in this case tennis. In the conclusion, she says that Andre is a morally good person. These are clearly two different senses of the word "good". The premise might be true but the conclusion can still be false: Andre might be the best tennis player in the world but a rotten person morally. Appropriately, since it plays on an ambiguity, this sort of fallacy is called the fallacy of equivocation, that is, equating two incompatible terms or claims.

Some fallacies are used frequently in the media and politics. For example, when one politician says to another, "You don't have the moral authority to say X", he is committing the argumentum ad hominem or personal attack fallacy — not addressing the argument but attacking the person who made it.

Arguably, the politician is not even attempting to make an argument, but is instead offering a moral rebuke. In this case there is no logically fallacious argument, but merely a personal opinion. Thus identifying logical fallacies may be difficult and dependent upon context.

In the opposite direction is the fallacy of argument from authority. A classic example is the Ipse dixit—"He himself said it" argument—used throughout the Middle Ages in reference to Aristotle. A modern instance is "celebrity spokespersons" in advertisements: a product is good and you should buy/use/support it because your favorite celebrity endorses it.

An appeal to authority is always a logical fallacy though it can be an appropriate form of rational argument if, for example, it is an appeal to expert testimony. In this case, the expert witness must be recognized as such and all parties must agree that the testimony is appropriate to the circumstances. This form of argument is common in legal situations.

By definition, arguments with logical fallacies are invalid, but they can often be (re)written in such a way that they fit a valid argument form. The challenge to the reader or listener is, of course, to discover the false premise, that is the premise which makes the argument unsound.

A list of fallacies

Please note that this list is not exhaustive.

See also

External links