How to Reason

A Practical Guide

Richard L. Epstein

• Publisher: Advanced Reasoning Forum
• Year: 2019
• eBook ISBN: 9781938421440
• Topic: Philosophy
• Subtopic: Logic in Philosophy

Too often we're guided by what we last heard, by our friends' approval, by impulse—our desires, our fears. Without reflection. Without even stopping to think. In this book you'll learn how to reason and find your way better in life. You'll learn to see the consequences of what you and others say and do. You'll learn to see the assumptions that you and others make. You'll learn how to judge what you should believe. These are the skills we all need to make good decisions. Illustrations using a cast of cartoon characters make the concepts memorable. And many exercises will help you to check your understanding. Truly a book for all—from high school to graduate school, from auto repair to managing a company. "How to Reason" will help you find a way in life that is clearer and not buffetted by the winds of nonsense and fear.

Reasoning from Experience

Arguing by analogy—“this is like that, so . . .”—is the most common way we draw on our experience. But though basic, such reasoning usually serves only as a suggestion for how to develop a good argument.

To fill out a comparison, we often need to make a claim about some group based on knowing about only a part of it. Such generalizations are not hard to evaluate once we see the criteria for what counts as a good one.

What we worry about most in our lives, though, is how to find a cause. Deciding whether to eat garlic, whether to take a job, whether to follow a doctor’s advice, we need to understand whether there is cause and effect. That’s not so hard to judge once we understand the criteria for what counts as cause and effect.

Often we ask “Why is this true?” An answer is typically an explanation we can judge according to clear enough criteria. But explanations about what is the function or goal of something are much harder to judge.

19Analogies

Analogies and comparisons

AnalogiesA comparison becomes reasoning by analogy when it’s part of an argument: on one side of the comparison we draw a conclusion, so on the other side we say we should conclude the same.

• We should legalize marijuana. After all, if we don’t, what’s the rationale for making alcohol and tobacco legal?

Alcohol is legal. Tobacco is legal. Therefore, marijuana should be legal. They are sufficiently similar. This is reasoning by analogy.

• DDT has been shown to cause cancer in rats. So there’s a good chance DDT will cause cancer in humans.

This is reasoning by analogy with an unstated comparison: Rats are like humans. Hence, if rats get cancer from DDT, so will humans.

• My love is like a red, red rose.— Robert Burns

This is not reasoning by analogy: there’s no argument.

Most reasoning by analogy is incomplete, relying on an unstated general principle. Often the value of an analogy is to uncover that principle.

• (Background: Country Joe McDonald was a rock star who wrote songs protesting the war in Vietnam. In 1995 he was interviewed on National Public Radio about his motives for working to establish a memorial for Vietnam War soldiers in Berkeley, California, his home and a center of antiwar protests in the ’60s and ’70s. This was his response.)
Blaming soldiers for war is like blaming firemen for fires.

Country Joe’s remark is a comparison. But it’s meant as an argument:

We don’t blame firemen for fires.

Firemen and fires are like soldiers and wars.
Therefore, we should not blame soldiers for war.

In what way are firemen and fires like soldiers and wars? They have to be similar enough in some respect for Country Joe’s remark to be more than suggestive. We need to pick out important similarities that we can use as premises.

Firemen and fires are like soldiers and war
wear uniforms
answer to chain of command
cannot disobey superior without serious consequences
fight (fires/wars)
work done when fire/war is over
until recently only men
lives at risk in work
fire/war kills others
firemen don’t start fires—soldiers don’t start wars
usually like beer

That’s stupid: Firemen and soldiers usually like beer. So?

When you ask “So?” you’re on the way to deciding if the analogy is good. It’s not just any similarity that’s important. There must be some crucial, important way that firemen fighting fires is like soldiers fighting wars, some similarity that can account for why we don’t blame firemen for fires that also applies to soldiers and war. Some of the similarities listed don’t seem to matter. Others we can’t use because they trade on an ambiguity, like saying firemen “fight” fires.

We don’t have any good guide for how to proceed—that’s a weakness of the original argument. But if we are to take Country Joe McDonald’s remark seriously, we have to come up with some principle that applies to both sides.

The similarities that seem most important are that both firemen and soldiers are involved in dangerous work, trying to end a problem/ disaster they didn’t start. We don’t want to blame someone for helping to end a disaster that could harm us all.

(‡)Firemen are involved in dangerous work.
Soldiers are involved in dangerous work.
The job of a fireman is to end a fire.
The job of a soldier is to end a war.
Firemen don’t start fires.
Soldiers don’t start wars.

But even with these added to the original argument, we don’t get a good argument for the conclusion that we shouldn’t blame soldiers for wars. We need a general principle:

You shouldn’t blame someone for helping to end a disaster that could harm others if he didn’t start the disaster.

This general principle seems plausible, and it yields a valid argument.

But is the argument good? Are all the premises true? This is the point where the differences between firemen and soldiers might be important.

The first two premises of (‡) are clearly true, and so is the third. But is the job of soldiers to end a war? And do soldiers really not start wars? Look at this difference:

Without firemen there would still be fires.

Without soldiers there wouldn’t be any wars.

Without soldiers there would still be violence. But without soldiers—any soldiers anywhere—there could be no organized violence of one country against another (“What if they gave a war and nobody came?” was an antiwar slogan of the Vietnam War era).

So? The analogy shouldn’t convince. The argument has a dubious premise.

We did not prove that soldiers should be blamed for wars. As always, when you show an argument is bad you haven’t proved that the conclusion is false. You’ve only shown that you have no more reason than before for believing the conclusion.

Perhaps the premises at (‡) could be modified, using that soldiers are drafted for wars. But that’s beyond Country Joe’s argument. If he meant something more, then it’s his responsibility to flesh it out. Or we could use his comparison as a starting place to decide whether there is a general principle, based on the similarities, for why we shouldn’t blame soldiers for war.

Steps in evaluating an analogy

•Is this an argument? What is the conclusion?

•What is the comparison?

•What are the similarities?

•Can we state the similarities as premises and find a general principle that covers the two s...

Table of contents

• Cover
• Title
• Copyright
• Contents
• Preface
• Claims
• Arguments
• The Form of an Argument
• Numbers and Graphs
• Reasoning from Experience
• Making Decisions
• Writing Well
• Index
• Dedication