!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> Streamline Training & Documentation: Favorite Fallacies

Monday, July 03, 2006

Favorite Fallacies

Below is a rogue's gallery of the more common fallacies to be alert to, followed by some tips for finding and eliminating such errors in reasoning.


Ad hoc explanation — After an event occurs, you offer an after-the-fact explanation that isn't really applicable. For example: "The fax was late because there is so much spam clogging the network."

Ad hominem attack — You attack the person making an argument rather than the argument itself. For example: "John is a naysayer. With his negative attitude, naturally he's against opening an office in Beijing."

Anecdotal evidence — Generalizing from individual instances without any assurance that the instances are representative. For example: "Crocodiles are moving into city parks. They found one in the Central Park reservoir yesterday."

Appeal to authority — You try to win support for an assertion by citing an authority who doesn't actually have relevant expertise. For example: "Tiger Woods says Wheaties is the best cereal."

Begging the question — You, in effect, assume what you are claiming to prove; or you offer what you are claiming to prove as evidence that your conclusion is true, i.e., you argue in circular fashion (see next item). (In this context, "begging" means "evading.") For example: "We need to add a week to the schedule because an extra week will help us."

Circular reasoning — You assume what you're claiming to prove. For example: "That idea will never work because it's completely impractical."

Fallacy of composition — It is assumed that something true of parts is also true of the whole that those parts comprise. For example: "If it's good for individuals to save more, it's good for everybody to save more." This is a favorite example of economists, who point out that our economy would generally be hurt if overall consumption were to fall due to an overall increase in saving.

False causality You decide that because B occurred after A, A caused B. (This fallacy is often referred to by its Latin name, "post hoc ergo propter hoc," i.e., "after this, therefore because of this." A similar fallacy is "cum hoc ergo propter hoc," i.e., "A and B happened at the same time; A must have caused B.") — For example: "As soon as we raised tuition reimbursement to 100%, employees started complaining more about our in-house training sessions taking too much time. They must prefer going to outside classes."

False dilemma — You tell people they have to pick A or B, implying that there are no other options. For example: "Either we figure out how to get our costs down 10%, or we're never going to be able to compete with Brand X."

Loaded question — You ask a question that contains an implied accusation. An example from the Institute for Teaching and Learning at San José State University: Your boss asks, "Can you begin to appreciate this wonderful opportunity I'm making available to you?"

New (old) is better — Arguing that something must be better — it's new! (The converse is arguing that something is better because it is long-established.) For example: "It's a new book on how to lose weight. Everybody with a weight problem should read it."

Non sequitur — You draw a conclusion that has no logical relationship to the premises from which you are arguing. For example: "Young consumers are spending more and more time at social networking sites on the Internet. I think we should switch to Linux on our servers."

Slippery slope — You argue that if A is allowed, a progression of bad events will ensue, but you don't demonstrate that there is a necessary connection between A occurring and the subsequent cascade of undesirable events. For example: "If we start providing free soda, people will start expecting yoghurt and peanuts. We can't afford that."

Straw man argument — You exaggerate or oversimplify an argument, and then show it's easy to knock the rephrased argument down. You conclude that this shows that the original argument is wrong. A wikipedia example: Person A says "I don't think children should run into the busy streets." Person B responds by saying, "I think that it would be foolish to lock up children all day with no fresh air." Person B thereby insinuates that person A's argument is far more draconian than it actually is.

Sweeping generalization — You argue that something which is broadly true is true of a particular instance, even though, in fact, it is not. For example: "Summer is a terrible time to sell parkas, so we should have them in our online catalog only between September and March."

Weak analogy — You claim two objects, ideas, or situations are alike, but they really aren't in the particular areas that are relevant. For example: "No matter what the boss says, trying to keep the general ledger free of errors is like making a hole-in-one every time you go out on the golf course. It's impossible."

You, too — You argue that an action is acceptable because the other person has also done it. (You may see this fallacy referred to by its Latin name, "Tu quoque.") For example: "But, Mom, you hitchhiked a lot when you were young. How come now you're saying it's a bad idea?"

The Writing Center at the University of North Carolina at Chapel Hill offers some suggestions for finding fallacies in your arguments:

Pretend you disagree with the conclusion you're defending — What parts of the argument would now seem fishy to you? What parts are easiest to attack? Give special attention to strengthening those parts.

List your main points and your evidence for each — Seeing your claims and evidence laid out this way may make you realize that you have no good evidence for a particular claim, or it may help you look more critically at the evidence you're using.

Learn which types of fallacies you're especially prone to — You can identify your favorite fallacies by looking back through some of your writings (e.g., memos). Check for these favorites when you review your work. Some people make lots of appeals to authority; others are more likely to rely on weak analogies or set up straw men. Etc.

Be aware that broad claims need more proof than narrow ones — Claims that use sweeping words like "all," "no," "none," "every," "always," "never," "no one," and "everyone," are sometimes appropriate — but they require a lot more proof than less sweeping claims that use words like "some," "many," "few," "sometimes," "usually," etc.

Double check your characterizations of others — Often, characterizations are simply irrelevant. If there is a good reason to characterize another person (e.g., you're writing a performance review), be sure you are fair and accurate.

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