Logical fallacy

A fallacy is a way that a logical argument can go wrong and thereby fail to be valid or sound, or otherwise fail to properly support its claim. Arguments intended to persuade may be convincing to many listeners despite containing such fallacies, but they are nonetheless flawed. Recognizing these fallacies is sometimes difficult.

Here is an example of a bad argument. Suppose James wanted to argue for the claim that all killing is wrong. Suppose he was giving this argument to a group of people who supported the death penalty: they think that some killing is fine, as punishment of the worst murderers. So James argues as follows:

1. If one should never do X, all X is wrong. (X can be any action.)
2. One should absolutely never kill.
3. Therefore, all killing is wrong.

The supporters of the death penalty would not be impressed by this argument. It commits the logical fallacy of begging the question. In the argument, James says that one should absolutely never kill. But to prove that, he would have to prove that all killing is wrong—which is what he is trying to argue for. Anyone who disagrees with the conclusion will disagree with the premise that one should absolutely never kill. One might maintain to the contrary that, indeed, in some cases one actually should kill: it is our grim duty, an unfortunate yet necessary part of justice.

The argument presupposes its conclusion: one of the premises assumes that the conclusion is true. This is an error in arguing. The kind of error has a name: begging the question. If James' argument begs the question, then in his argument he assumes the very thing that he is trying to argue for. Of course an argument that begs the question will not, or should not, convince anyone.

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

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. Those are clearly two different senses of the word "good." So, of course, the premise might be true while the conclusion would still be false: Andre might be the best tennis player in the world but a rotten person morally speaking. Appropriately, since it plays on an ambiguity, this sort of fallacy is called the Fallacy of Equivocation.

Some fallacies are used freely in the media and politics. For example, the argumentum ad hominem, or personal attack, is used when instead of refuting an statement, the person who made that statement is attacked. Every time a politician says to another politician, "You don't have moral authority to say that" is using that fallacy, not attacking the argument, but the person who uses it. Strictly speaking, this is a fallacy; but, arguably, the politician is not even making an argument, but is instead offering a moral rebuke. This is an example of the difficulty of helpfully and respectfully identifying fallacies as such; it is more difficult than it might at first appear, e.g. to a student armed with a list of fallacies.

In the opposite direction is the fallacy of argument from authority. A classic example of this is the Ipse dixit[?]—"He himself (the master) said it"—used through the Middle Ages in reference to Aristotle. A modern use of this is "celebrity spokepersons" in advertisements: that product is good because your favorite celebrity endorses it.

Sometimes, however, an appeal to an authority is best construed not as a fallacy but as an appeal to expert testimony[?]—a type of inductive argument. This is another example of the difficulty of identifying fallacies as such.

Typically, logical fallacies are invalid, but they can often be written or rewritten so that they follow a valid argument form; and in that case, the challenge is to discover the false premise, which makes the argument unsound.

There are some argument forms that are themselves invalid, however. One of the best-known examples is affirming the consequent.

An incomplete list of fallacies

• Ad hominem tu quoque (also called the "hypocrisy argument")
• Affirming the consequent
• Appeal to authority
• Appeal to belief
• Appeal to common practice (also Appeal to tradition; Argument ad antiquitam)
• Appeal to consequences of a belief
• Appeal to emotion
• Appeal to fear (Argument ad metum)
• Appeal to force
• Appeal to flattery
• Appeal to novelty (Argument ad novitam)
• Appeal to pity (Argument ad misericordiam)
• Appeal to ridicule
• Appeal to spite (Argument ad odium)
• Argumentum ad baculum (or generally an Appeal to force)
• Argumentum ad nauseam (or Argument from repetition)
• Argument from fallacy
• Argument from ignorance
• Argumentum e(x) silentio (or Argument from silence)
• Bandwagon fallacy (also called Appeal to popularity)
• Begging the question (Circular argument)
• Biased sample
• Shifting the Burden of proof
• Correlative based fallacies
• Composition
• Confusing cause and effect
• Correlation implies causation
• Denying the correlative
• Division
• Equivocation
• False dilemma or Excluded middle
• Varieties of faulty generalization:
  • Hasty generalization (Leaping to a conclusion, The lonely fact)
  • Overwhelming exception
  • Statistical special pleading
• Gambler's fallacy
• Genetic fallacy
• Guilt by association
• Ignoratio elenchi (Irrelevant conclusion)
• Lack of imagination
• Fallacy of many questions
• Meaningless statement
• Middle ground (Argument ad temperantiam)
• Misleading vividness
• Naturalistic fallacy
• Negative proof
• Non sequitur (It does not follow..)
• No true Scotsman
• Package deal fallacy
• Pathetic fallacy (Thinking of inanimate objects like they were animate)
• Personal attack, or argumentum Ad hominem or Poisoning the well
• Prosecutor's fallacy
• Post hoc
• Questionable cause
• Red herring
• Reification (Hypostatization)
• Relativist fallacy
• Slippery slope
• Special pleading
• Spotlight
• Straw man
• Suppressed correlative
• Two wrongs make a right

See also

• Fallacies of definition
• Good argument
• Validity
• Soundness
• Cogency
• College logic
• Informal logic

External links

• The Fallacy Files (http://gncurtis.home.texas.net/)
• Stephen's Guide to the Logical Fallacies (http://www.intrepidsoftware.com/fallacy/welcome.htm)
• Logic & Fallacies, from Atheism Web (http://www.infidels.org/news/atheism/logic) (no strict relation to Atheism)