Inductive Arguments Study Guide

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.