6a. Distinguishing between reasonable and fallacious argumentative tactics

6aDistinguish between reasonable and fallacious argumentative tactics.

When you evaluate an argument, look closely at the reasoning and evidence behind it. Some unreasonable argumentative tactics are known as logical fallacies. Most of the fallacies—such as hasty generalizations and false analogies—are misguided or dishonest uses of legitimate strategies. The examples in this section suggest when such strategies are reasonable and when they are not.

Generalizing (inductive reasoning)

Writers and thinkers generalize all the time. We look at a sample of data and conclude that data we have not observed will most likely conform to what we have seen. From a spoonful of soup, we conclude just how salty the whole bowl will be. After numerous unpleasant experiences with an airline, we decide to book future flights with a competitor.

When we draw a conclusion from an array of facts, we are engaged in inductive reasoning. Such reasoning deals in probability, not certainty. For a conclusion to be highly probable, it must be based on evidence that is sufficient, representative, and relevant. (See the chart at the bottom of the page.)

The fallacy known as hasty generalization is a conclusion based on insufficient or unrepresentative evidence.

hasty generalization

In a single year, scores on standardized tests in California’s public schools rose by ten points. Therefore, more children than ever are succeeding in America’s public school systems.

Data from one state do not justify a conclusion about the whole United States.

A stereotype is a hasty generalization about a group. Here are a few examples.

stereotypes

Women are bad bosses.

Politicians are corrupt.

Children are always curious.

Stereotyping is common because of our human tendency to perceive selectively. We tend to see what we want to see; we notice evidence confirming our already formed opinions and fail to notice evidence to the contrary. For example, if you have concluded that politicians are corrupt, your stereotype will be confirmed by news reports of legislators being indicted—even though every day the media describe conscientious officials serving the public honestly and well.

Academic English

Many hasty generalizations contain words such as all, ever, always, and never, when qualifiers such as most, many, usually, and seldom would be more accurate.

Drawing analogies

An analogy points out a similarity between two things that are otherwise different. Analogies can be an effective means of arguing a point. It is not always easy to draw the line between a reasonable and an unreasonable analogy. At times, however, an analogy is clearly off base, in which case it is called a false analogy.

false analogy

If we can send a spacecraft to Pluto, we should be able to find a cure for the common cold.

How are these ideas related? The writer has falsely assumed that because two things are alike in one respect, they must be alike in others. Exploring the outer reaches of the solar system and finding a cure for the common cold are both scientific challenges, but the problems confronting medical researchers are quite different from those solved by space scientists.

Tracing causes and effects

Demonstrating a connection between causes and effects is rarely simple. For example, to explain why a chemistry course has a high failure rate, you would begin by listing possible causes: inadequate preparation of students, poor teaching, lack of qualified tutors, and so on. Next you would investigate each possible cause. Only after investigating the possible causes would you be able to weigh the relative impact of each cause and suggest appropriate remedies.

Because cause-and-effect reasoning is so complex, it is not surprising that writers frequently oversimplify it. In particular, writers sometimes assume that because one event follows another, the first is the cause of the second. This common fallacy is known as post hoc, from the Latin post hoc, ergo propter hoc, meaning “after this, therefore because of this.”

post hoc fallacy

Since Governor Cho took office, unemployment among minorities in the state has decreased by 7 percent. Governor Cho should be applauded for reducing unemployment among minorities.

Is the governor solely responsible for the decrease? Are there other reasons? It is not enough to show that the decrease in unemployment followed the governor’s taking office.

Weighing options

Especially when reasoning about problems and solutions, writers must weigh options. To be fair, a writer should mention the full range of options, showing why one is superior to the others or might work well in combination with others.

It is unfair to suggest that there are only two alternatives when in fact there are more. Writers who set up a false choice between their preferred option and one that is clearly unsatisfactory are guilty of the either . . . or fallacy.

either . . . or fallacy

Our current war against drugs has not worked. Either we should legalize drugs or we should turn the drug war over to our armed forces and let them fight it.

Are these the only solutions—legalizing drugs and calling out the army? Other options, such as funding for drug abuse prevention programs, are possible.

Making assumptions

An assumption is a claim that is taken to be true—without the need of proof. Most arguments are based to some extent on assumptions since writers rarely have the time and space to prove all of the conceivable claims on which their argument is based. For example, someone arguing about the best means of limiting population growth in developing countries might assume that the goal of limiting population growth is worthwhile. For most audiences, there would be no need to articulate this assumption or to defend it.

There is a danger, however, in failing to spell out and prove a claim that is clearly controversial. Consider the following short argument, in which a key claim is missing.

argument with missing claim

Violent crime is increasing. Therefore, we should vigorously enforce the death penalty.

The writer seems to be assuming both that the death penalty deters violent criminals and that it is a fair punishment—and that most readers will agree. These are not reasonable assumptions; the writer will need to state and support both claims.

When a missing claim is an assertion that few would agree with, we say that a writer is guilty of a non sequitur (Latin for “does not follow”).

non sequitur

Christopher gets plenty of sleep; therefore, he will be a successful student in the university’s pre-med program.

Does it take more than sleep to be a successful student? The missing claim—that people with good sleep habits always make successful students—would be hard to prove.

Deducing conclusions (deductive reasoning)

When we deduce a conclusion, we put things together, like any good detective. We establish that a general principle is true, that a specific case is an example of that principle, and that therefore a particular conclusion about that case is a certainty.

Deductive reasoning can often be structured in a three-step argument called a syllogism. The three steps are the major premise, the minor premise, and the conclusion.

  1. Anything that increases radiation in the environment is dangerous to public health. (Major premise)
  2. Nuclear reactors increase radiation in the environment. (Minor premise)
  3. Therefore, nuclear reactors are dangerous to public health. (Conclusion)

The major premise is a generalization. The minor premise is a specific case. The conclusion follows from applying the generalization to the specific case.

Deductive arguments break down if one of the premises is not true or if the conclusion does not follow logically from the premises. In the following short argument, the major premise is very likely untrue.

untrue premise

The police do not give speeding tickets to people driving less than five miles per hour over the limit. Dominic is driving fifty-nine miles per hour in a fifty-five-mile-per-hour zone. Therefore, the police will not give Dominic a speeding ticket.

The conclusion is true only if the premises are true. If the police sometimes give tickets for driving less than five miles per hour over the limit, Dominic cannot safely conclude that he will avoid a ticket.

In the following argument, both premises might be true, but the conclusion does not follow logically from them.

conclusion does not follow

All members of our club ran in this year’s Boston Marathon. Jay ran in this year’s Boston Marathon. Therefore, Jay is a member of our club.

The fact that Jay ran the race is no guarantee that he is a member of the club. Presumably, many runners are nonmembers.

Assuming that both premises are true, the following argument holds up.

conclusion follows

All members of our club ran in this year’s Boston Marathon. Jay is a member of our club. Therefore, Jay ran in this year’s Boston Marathon.

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  • Academic reading and writing > As you write: Evaluating ads for logic and fairness

Testing inductive reasoning

Though inductive reasoning leads to probable and not absolute truth, you can assess a conclusion’s likely probability by asking three questions. This chart shows how to apply those questions to a sample conclusion based on a survey.

conclusion The majority of students on our campus would volunteer at least five hours a week in a community organization if the school provided a placement service for volunteers.
evidence In a recent survey, 723 of 1,215 students questioned said they would volunteer at least five hours a week in a community organization if the school provided a placement service for volunteers.

1. Is the evidence sufficient?

That depends. On a small campus (say, 3,000 students), the pool of students surveyed would be sufficient for market research, but on a large campus (say, 30,000), 1,215 students are only 4 percent?of the population. If those 4 percent were known to be truly representative of the other 96 percent, however, even such a small sample would be sufficient (see question 2).

2. Is the evidence representative?

Only if those responding to the survey reflect the characteristics of the entire student population: age, sex, race, field of study, number of extracurricular commitments, and so on. If most of those surveyed are majors in a field like social work, the researchers should question the survey’s conclusion.

3. Is the evidence relevant?

Yes. The survey results are directly linked to the conclusion. A survey about the number of hours students work for pay would not be relevant because it would not be about choosing to volunteer.