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We often have lapses in critical thinking as we speak and write. A fallacy is a belief or argument that rests on invalid or false inference that is logically unsound. Fallacies are often used unintentionally, but they are also used intentionally when an effort is being made to deceive or mislead the listener or reader.
1. "If you know about BMW, you either own one or you want one."
What's wrong with this statement? It is an example of the fallacy called false alternatives. It is also called dualistic or black-and-white thinking and bifurcation. The fallacy occurs when it is presumed that a classification is exclusive or exhaustive. It often takes the form of overlooking alternatives that exist between two polar opposites.
Here is another example of false alternatives written by an educator who was suggesting that children should begin public school at the age of four and that high school should end after the eleventh year: "Twelfth grade has become a bore for able students and a holding tank for the rest."
2. "I asked my doctor why my mouth was so dry and he told me that it was because my saliva glands are not producing enough saliva."
What do you think of the doctor's diagnosis? This is an example of the fallacy of begging the question, or circularity. The fallacy occurs when the solution to a problem is a restatement of the problem, or, an argument for a proposition is equivalent to the proposition, such as "He throws tantrums all the time because he has a terrible temper." Diagnoses of mental disorders are sometimes considered to beg the question: "Why is he so nervous and agitated?" "He has generalized anxiety disorder." "What does that mean?" "It means that he has anxiety and apprehension."
Here is another example that may seem ridiculous, but when things such as this occur in the context of speech or writing, they often sound all right, maybe even impressive: "Bodies fall because they have a downward tendency."
3. "He is an innocent man. He was tried before a jury of his peers and the prosecution was unable to prove him guilty."
Is the assumption of innocence justified? This is an example of the fallacy called appeal to ignorance. This fallacy occurs when it is argued that because we cannot prove a proposition to be true, it must be false; or if we cannot prove a proposition to be false, it must be true.
Here is another example: "There has never been any scandal about this candidate for president. Therefore, he must be an honest, moral person."
4. "If you don't pick up your clothes before you go to bed at night, pretty soon you'll be knee-deep in dirty clothes."
Is that the way it is? This is an example of the fallacy called slippery slope; certain applications of it have been called the domino theory. The argument is that if the first in a possible series of steps or events occurs, the other steps or events are inevitable.
Here is an example from a letter to the editor of a metropolitan newspaper. The writer was responding to an article discussing the morality of euthanasia in the case of a person with an advanced case of multiple sclerosis: "If we allow this to happen, where do we stop? Who would decide at what point someone should die? Do we give them poison the moment they know they have multiple sclerosis or cancer, before they have any suffering?"
5. "TV can't be harmful for children because it occupies their attention for hours and keeps them off the streets."
Is this argument against the idea that TV can be harmful for children convincing? It is an example of the fallacy called irrelevant reason. This fallacy occurs when the argument given to support a proposition has little or no relevance to the proposition.
Here is another example: "Conservationists have suggested that we could conserve fuel by increasing the tax on gasoline. But more taxes, whether they're paid by the oil companies or passed on to the consumer at the pump, will not produce one more barrel of oil."
6. "I don't see how she can get elected. No one I know is going to vote for her."
What's wrong with this argument? This is the fallacy called hasty generalization. It occurs when an isolated or exceptional case is used as the basis for a general conclusion. In more statistical language, it is making a conclusion about a population based on information obtained from a sample that is biased or too small. It is an error of inductive reasoning—going from the particular to the general when it is not justified by the evidence.
Another example is attributed to the brother of a former president of the United States: "I never read a book by a woman because I never met a woman who had sense enough to write a book." (Either he hasn't met very many women, in which case the sample is too small, or the ones he has met are a biased sample. Of course, there is the possibility that he is a devout sexist.)
7. "If socialized medicine will result in better and lower-cost healthcare, shouldn't the same logic be applied to automobiles? Wouldn't nationalization of the auto industry produce better and lower-cost cars? And if we nationalized auto mechanics, wouldn't we get better and less-expensive repairs?"
These words were spoken in rebuttal after Senator Kennedy had called for national health insurance in a speech at a meeting of the United Auto Workers. Does the speaker's argument make sense? It represents the fallacy called questionable analogy. In questionable analogy an attempt is made to make two situations seem more similar than they actually are.
Another example is from a state senator who was using the crucifixion as a rationale for capital punishment: "Where would Christianity be if Jesus got 8 to 15 years with time off for good behavior?"
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