Fallacies are statements that may sound reasonable or true but are not logically defensible and may actually be deceptive. When your readers detect them, such statements can backfire and turn even a sympathetic audience against your position. Here are some of the more common fallacies that you should try to avoid:
Begging the Question
Begging the question is a logical fallacy that assumes in the premise what the arguer is trying to prove in the conclusion. This tactic asks readers to agree that certain points are self-evident when they are not.
The unfair and shortsighted legislation that limits free trade is clearly a threat to the American economy.
Restrictions against free trade may or may not be unfair and shortsighted, but emotionally loaded language does not constitute proof. The statement begs the question because it assumes what it should be proving-that restrictive legislation is dangerous.
Ignoring the Question
a question is set up so that argument is shifted to new ground, or an appeal is made to some emotional attitude having nothing to do with the logic of the case.
You should talk about the apartheid philosophy in Africa. Do you know what Americans did to the Indians?
Argument from Analogy
An analogy is a comparison of two unlike things. Although analogies can explain an abstract or unclear idea, they are not proof. An argument that is based on an analogy and ignores important dissimilarities between the two things being compared is a fallacy.
The overcrowded conditions in some parts of our city have forced people together like rats in a cage. Like rats, they will eventually turn on one another, fighting and killing until a balance is restored. It is therefore necessary that we vote to appropriate funds to build low-cost housing.
No evidence is offered that people behave like rats under these or any other conditions. You should not assume that simply because two things have some characteristics in common, they are alike in other respects.
Personal Attack (Argument Ad Hominem)
This fallacy tries to turn attention away from the facts of an issue by attacking the motives or character of one's opponents.
The public should not take seriously Dr. Mason's plan for upgrading county health services. He is a recovering alcoholic whose second wife recently divorced him.
This attack on Dr. Mason's character says nothing about the quality of his plan. Sometimes a connection exists between a person's private and public lives--for example, a case of conflict of interest. But no evidence of such a connection is given here.
Hasty or Sweeping Generalization
A form of jumping to a conclusion, this fallacy occurs when a conclusion is reached on the basis of too little evidence.
Our son Marc really benefited socially from going to nursery school; I think every child should go.
Perhaps other children would benefit from nursery school, and perhaps not, but no conclusion about children in general can be reached on the basis of one child's experience.
False Dilemma (Either/Or Fallacy)
This kind of argument assumes that there are only two alternatives when more exist.
We must choose between life and death, between intervention and genocide. There can be no neutral position on this issue.
An argument like this oversimplifies issues and forces people to choose between extremes instead of exploring more moderate positions.
This fallacy occurs when the meaning of a key term changes at some point in an argument. Equivocation makes it seem as if a conclusion follows from premises when it actually does not.
As a human endeavor computers are a praiseworthy and even remarkable accomplishment. But how human can we hope to be if we rely on computers to make our decisions?
The use of human in the first sentence refers to the entire human race. In the second sentence human means "merciful" or "civilized." By subtly shifting this term to refer to qualities characteristic of people as opposed to machines, the writer makes his argument seem more sound than it is.
This fallacy occurs when the focus of an argument is changed to divert the audience from the actual issue.
So far Mr. Bradley, our state representative, has spent months fighting the proposed tax bill. The governor has said that she needs the revenue that this bill offers, but Mr. Bradley refuses to support her. One can only wonder if Mr. Bradley has nothing better to do in his own district than to spend so much time opposing the governor.
The focus of this argument should be the merits of the tax bill. Instead, the writer shifts to the irrelevant issue of Mr. Bradley's spending too much time opposing the governor.
You Also (Tu Quoque)
This fallacy asserts that an opponent's argument has no value because the opponent does not follow his or her own advice. In other words, an opponent is accused of acting in a way that is not in line with his or her stated position.
How can that judge favor stronger penalties for convicted drug dealers? During his confirmation hearings, he admitted having smoked marijuana when he was a student.
Appeal to Doubtful Authority
Often people will attempt to bolster an argument with references to experts or famous people. These appeals are valid when the person quoted or referred to is an expert in the area being discussed. They are fallacies, however, when the individuals cited have no expertise concerning the issue.
According to Ted Koppel, interest rates will remain low during the next fiscal year.
Although Ted Koppel is a respected journalist, he has no background in business or finance. In the final analysis, his pronouncements about interest rates are no more than a personal opinion or, at best, an educated guess.
Although statistics are a powerful form of factual evidence, they can be misrepresented or distorted in an attempt to influence an audience.
Women will never be competent electricians; 50 percent of the women in the electrical technology section failed the exam.
Here the writer has neglected to mention that there were only two women in the course. Because this statistic is not based on a large enough sample, it cannot be used as evidence to support the argument.
Post Hoc, Ergo Propter Hoc (After This, Therefore Because of This)