Inductive Arguments Study Guide (page 3)

Lesson Summary

The deductive method is the mode of using knowledge, and the inductive method the mode of acquiring it.

Henry Mayhew, English journalist and playwright (1812–1887)

You just investigated deductive arguments, the kind built on laws and principles, that move from generalizations to specific conclusions. Now it's time to look at the other kind of reasoning: inductive arguments. They're built on common sense and/or past experience, moving from specific facts to general conclusions. In this lesson, you'll learn to recognize and construct arguments that use inductive reasoning.

Induction is the process of reasoning from specific facts or occurrences to general principles, theories, and rules. Used in scientific hypotheses, inductive thinking uses two conditional premises that support a probable truth in the conclusion: If A is true and B is true, then C is probably true.

In inductive reasoning, we determine or measure what's probable or improbable by using two things:

1. past experience
2. common sense

Past experience lets you predict what you think might happen the next time there's a similar situation. For example, "For the past three weeks, Bob's been a half-hour late for work. Today, he'll probably be late again."

Common sense allows you to make an inference, or "smart guess," based on known facts or premises. For example, "They must have five people on their team. I'm one of the best of the seven players at the tryouts. So it's likely I'll be picked for the team."

You learned that in deductive reasoning, a conclusion had to be true if the premises were true. But with inductive reasoning, the premises are good reasons for thinking the conclusion is correct, but there's always a possibility that, although the premises are true, the conclusion will be false. In other words, there's no automatic, logical link between premises and conclusion. So inductive reasoning is more likely than deductive reasoning to fail and produce fallacies, like a hasty conclusion fallacy.

Even with its flaws, inductive reasoning is the type of reasoning we use most often. The cell theory, one of the basics of modern biology, is a product of inductive reasoning: Every organism observed is made up of cells; therefore, it is most likely that all living things are made up of cells.

There are two forms of inductive arguments: comparative arguments match one thing, event, or idea up against another to see if they're similar; causal arguments try to determine cause from effect.

Tip

In science, inductive reasoning is essential for discovering relationships as you create logical hypotheses and theories.

Comparison Arguments

Inductive arguments compare one event, idea, or thing with another to conclude if they are similar enough to make a generalization or inference about them. The most important characteristic of the argument is that the two events being compared must be similar.

Example

Rebekah is comparing one thing (use of bread flour for pizza crust) with another (bread flour producing a perfect crust). The two things have one similarity: bread flour. The inductive argument produces a generalization: Any time she uses bread flour to make pizza dough, she'll get perfect pizza crust.

The strength of this, as well as all other, comparative inductive arguments depends on how similar the two things are. In fact, when an inductive argument fails, it is most often because the events were not really similar enough to make a comparison. Rebekah takes for granted that "every time" in the future, she will make pizza exactly as she did during each of the observed times. If that is true, her conclusion is probably true.

But what if every observed time Rebekah used the bread flour, she also used fresh yeast? If she makes a pizza in the future with packaged yeast, she will not get a perfect crust. The events will be dissimilar, so the conclusion will not hold. The second premise of any inductive argument should ideally state that there is no significant difference between the two sets of events/ ideas/things. The second premise of Rebekah's argument could say "Every crust will be perfect, because there will be no key difference between my future crust making and my previous crust making." Keeping such disclaimer in mind is important, because this is where many inductive arguments are weakest.

Causal Arguments

The previously mentioned inductive arguments relied on the similarities between two things. Causal arguments rely instead on finding a key difference to determine the probable cause of an effect. Why is it important to determine cause? If you believe that one thing is the reason (cause) that another thing happened (effect), you may want to either (1) reproduce that relationship and cause that effect again, or (2) prevent the relationship from happening again.

For example, every time you study hard for a test, you get a good grade. If you want to keep getting good grades, you want to know if there is a link between studying hard and getting good grades. When you can determine cause and effect, you can repeat the effect. In this case, that means figuring out that the studying really does result in good grades. To continue to get good grades, therefore, you need to continue to study hard for every test.

On the other hand, what if you have been studying and getting good grades and there is a test coming up? You are busy with other things and don't study for it. You get a D on the test. The argument goes like this:

Every time I have a test coming up, I study for it and get good grades. This time, I didn't study, and I got a D. If I don't want to get more Ds in the future, I'll prevent the unwanted result by preventing the cause. In this case, the key difference means if you don't want bad grades, you must study. Remember that in order to determine cause, an argument must be formed that looks for a key difference between two otherwise similar events.

Here is another example:

Jen had a stomachache on Thursday and is trying to figure out why. Every morning for breakfast she eats bran cereal with skim milk and a banana. But on Thursday she was out of milk and had toast for breakfast instead. By midmorning, she had a painful stomachache. She picked up milk on the way home from work and had her usual breakfast on Friday. The stomachache did not occur on Friday. Nothing else in her routine was out of the ordinary.

What caused the stomachache? Chances are it was the breakfast she ate on Thursday. It's the key difference. Every morning when she eats her regular breakfast, she feels fine, but gets a stomachache the one morning she eats only toast instead. Perhaps she was hungry, having had less to eat. However, not all examples are this easy to spot. It may require an inference based on information in the argument.

Real-life situations can get complicated. Our lives and the world around us are affected by thousands of details, making the finding of one key difference difficult. That said, if there is a strong likelihood of causation and there are no other obvious causes, you can make a convincing causal argument. But you need to have the following:

• The effect must occur after the cause. This sounds like common sense, but there are many arguments that place the effect before the cause.

Example

You are blamed for a computer problem at work. However, you did not use the computer until after the problem was detected. The argument against you has no strength.

• You need more than just a strong correlation to prove causation. Coincidence can often explain what might first appear to be cause and effect.