Logical fallacy

A logical fallacy is, fundamentally, an error in logic.

Formal fallacies

Formal fallacies are those fallacies that violate a particular rule of propositional calculus, such as modus ponens. These fallacies can be determined to be invalid simply by the inspection of their form.

Informal fallacies

Informal fallacies are arguments that, while not violating propositional calculus rules, are invalid because of the content of their argument.

Common fallacies include:

• Ad hoc -- Using an off-the-cuff explanation with no evidentiary support.
• Ad hominem -- Attacking the opponent directly rather than addressing the opponent's idea (a favorite tactic of the likes of Ann Coulter, Rush Limbaugh and nearly everyone at Fox News); also, tu quoque, where a criticism is falsely dismissed because its author is also guilty of the charge.
• Argument by assertion - The belief that if you say a thing enough times, it becomes true and you win the argument.
• Argument from ignorance -- Basing the truth of a premise only on whether it has been proved to your satisfaction.
• Argument from incredulity -- Literally "that's unbelievable = that's obviously not real". This kind of thinking would quickly put an end to virtually all quantum physics.
• Argument from adverse consequences -- Arguing against a point based on expected negative outcome.
• Argument from authority -- Because someone famous/powerful/respected believes it, it must be true.
• Balance fallacy -- Giving equal weighting to both sides of an argument, even if one really doesn't deserve the time.
• Begging the question -- Assuming the conclusion as part of the premise (similar to circular reasoning).
• Correlation does not equal causation -- The number of pirates on the seas has gone down, this correlates with global temperatures rising. So, do pirates cause global cooling?
• Equivocation -- Deliberately substituting the meaning of a given word in one context for another context that is inappropriate in order to make your argument.
• Ex equus pyga -- "From the horse's ass" is a variety of argument from authority. The horse's ass claims former military or government service to lend weight to their assertions or imperatives.
• False analogy -- Creating an analogy or metaphor, then extending it to prove one's point.
• False dilemma -- Portraying two options as the only possibilities, with no middle ground (see Pascal's wager for an example).
• Moving the goalposts -- Changing evidential requirements in an argument once they have been met, "what I really meant was..."
• Negative proof -- Arguing that something must exist because there is no evidence it does not exist.
• No True Scotsman -- Excluding an inconveniently misbehaving member of a class to defend the class as a whole.
• Non sequitur -- Giving an evasive or nonsensical answer to a challenge.
• One single proof -- Dismissing all circumstantial evidence in favor of a single "smoking gun" that may not (and may not need to) exist.
• Poisoning the well -- Attempting to refute an argument based on the perceived veracity of the presenter.
• Post hoc, ergo propter hoc -- Saying that because event A happened before B, A must have caused B.
• Red herring -- a group of fallacies which bring up a fact which is irrelevant to the issue.
  • Guilt by association -- Saying that something is bad because a bad person or group did it, i.e. saying painting is evil because Hitler liked to paint (see also Godwin's law) or ties are immoral because Bush wears ties.
  • Honor by association -- Saying that something is good because a good person or group did it.
  • My enemy's enemy -- Supporting someone because they oppose the same people
  • Argumentum ad baculum -- Attempting to intimidate an opponent (baculum is Latin for "stick").
  • Argumentum ad populum or bandwagon -- Arguing for a point based on popularity rather than merit.
  • Argumentum ad verecundiam -- "Argument from shame". Also see emotional appeal.
• Slippery slope -- If event A happens, it will lead downhill to further undesirable results. For example, "if we allow gays to get married, then we'll have to let men marry little kids".
• Spotlight fallacy -- Assuming aspects of a group from aspects from a smaller observed part of the group
• Straw man -- Falsifying an opponent's position for greater rhetorical flexibility.
• Style over substance fallacy -- Using language or rhetoric to enhance the appeal of an argument, but not its validity.
• Texas sharpshooter -- A data mining fallacy and pattern recognition error where the arguer makes an ad hoc conclusion from a set of unrelated data without looking for corroborating data.
• The Galileo fallacy -- This states that if someone is going against the tide of popular thinking, they must be right because the likes of Galileo were right, while in reality, Galileo was right for the more simple reason that he was right.
• Causalation -- See correlation does not equal causation.

See also

• Occam's razor
• The Fine Art of Baloney Detection
• Rhetoric
• List of cognitive biases

External links

• Logical Fallacy on Wikipedia
• The Fallacy Files