Printed Page 182-183
Avoiding Logical Fallacies
A logical fallacy—that is, a mistake in reasoning—can undercut the persuasiveness of your writing. An example is “Antidepressants are a scam; I know that because Tom Cruise says so, and he’s a world-famous actor.” Although Tom Cruise is a world-famous actor, it does not follow that what he thinks about antidepressants is true. Table 8.1 explains some of the most common logical fallacies.
| TABLE 8.1 Common Logical Fallacies | ||
| FALLACY | EXPLANATION | EXAMPLE AND COMMENT |
| Ad hominem argument; also called argument against the speaker | An argument against the writer, not against the writer’s argument |
“Of course Matthew wants us to buy more computers—he’s a computer geek.” The fact that Matthew is a “computer geek” doesn’t necessarily mean that his argument for buying more computers is unwise. |
| Argument from ignorance | An argument that a claim is true because it has never been proven false, or false because it has never been proven true |
“Nobody has ever proven that global warming is occurring. Therefore, global warming is a myth.” The fact that a concept has not yet been proven does not necessarily mean that it is false. Perhaps the measurement techniques are insufficiently precise or not yet available. |
| Appeal to pity | An argument based on emotion, not reason |
“We shouldn’t sell the Ridgeway division. It’s been part of the company for over 40 years.” The fact that the division has long been a part of the company is not in itself a good reason to retain it. |
| Argument from authority | An argument that a claim is valid because the person making the claim is an authority |
“According to world-renowned climatologist Dr. William Smith, global warming is definitely a fact.” Even if Dr. Smith is a recognized authority in this field, the claim that global warming is a fact is not valid unless you present a valid argument to support it. |
| Circular argument | An argument that restates its main point without presenting any evidence to support it |
“Facebook’s stock price keeps falling because the company’s value is still going down.” Because a company’s stock price is a measure of the company’s value, the argument simply says that Facebook’s stock price keeps falling because its stock price keeps falling. Using the word because doesn’t necessarily mean that the writer has presented a reason. The writer needs to explain why the stock price keeps going down. |
| Either-or argument | An argument that poses only two alternatives when in fact there might be more |
“Either we start selling our products online or we’re going to be out of business within a year.” This statement does not explain why these are the only two alternatives. The company might improve its sales by taking measures other than selling online. |
| Ad populum argument; also called bandwagon argument | An argument that a claim is valid because many people think it is or act as if it is |
“Our four major competitors have started selling online so we should, too.” The fact that our competitors are selling online is not in itself an argument that we should sell online, too. |
| Hasty generalization; sometimes called inadequate sampling | An argument that draws conclusions based on an insufficient number of cases |
“The new Tata is an unreliable car. Two of my friends own Tatas, and both have had reliability problems.” To reach any valid conclusions, you would have to study a much larger sample and compare your findings with those for other cars in the Tata’s class. |
| Post hoc reasoning (the complete phrase is post hoc, ergo propter hoc) | An argument that claims that because A precedes B, A caused B |
“There must be something wrong with the new circuit breaker in the office. Ever since we had it installed, the air conditioners haven’t worked right.” Maybe the air conditioners are malfunctioning because of the circuit breaker, but the malfunction might have other causes. |
| Oversimplifying | An argument that omits important information in establishing a causal link |
“The way to solve the balance-of-trade problem is to improve the quality of the products we produce.” Although improving quality is important, international trade balances are determined by many factors, including tariffs and currency rates, and therefore cannot be explained by simple cause-and-effect reasoning. |