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Inductive vs Deductive Reasoning Help (page 3)

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Updated on Sep 29, 2011

Identifying the Overall Conclusion

Read the following sentences:

He's tall, so he must be a good basketball player. All tall people are good basketball players.

These two sentences represent a small deductive argument. It's not a particularly good argument, but it is a good example of deductive structure. If these two sentences are broken down into their parts, three different claims arise:

  1. He's tall.
  2. He must be a good basketball player.
  3. All tall people are good basketball players.

Now ask the key question: "What is this argument trying to prove?" In other words, what is the conclusion?

Two clues should help you come up with the right answer. First, look at which claims have support (evidence) in this example. Is there anything here to support the claim that "He is tall"? No. Is there anything to support the claim, "All tall people are good basketball players"? No. But there are premises to support the claim, "He must be a good basketball player." Why must he be a good basketball player? Because:

  1. He is tall.
  2. All tall people are good basketball players.

Therefore, the conclusion of this argument is: "He must be a good basketball player." That is what the writer is trying to prove. The premises that support this conclusion are "He is tall" and "All tall people are good basketball players."

A second clue in the conclusion that "He must be a good basketball player" is the word so. Several key words and phrases indicate that a conclusion will follow. Similarly, certain words and phrases indicate that a premise will follow:

Indicate a Conclusion:

  • Accordingly
  • As a result
  • Consequently
  • Hence
  • It follows that
  • So
  • That's why
  • Therefore
  • This shows/means/suggests that
  • Thus

Indicate a Premise:

  • As indicated by
  • As shown by
  • Because
  • For
  • Given that
  • Inasmuch as
  • Since
  • The reason is that

Now, are the premises that support the conclusion, "He must be a good basketball player," separate support or chain support?

You should be able to see that these premises work together to support the conclusion. "He is tall" alone doesn't support the conclusion, and neither does "All tall people are good basketball players." But the two premises together provide support for the conclusion. Thus, the example is considered a chain of support argument.

The Position of the Conclusion

While you might be used to thinking of the conclusion as something that comes at the end, in a deductive argument, the conclusion can appear in different places. Here is the same argument rearranged in several different ways:

  • He must be a good basketball player. After all, he's tall, and all tall people are good basketball players.
  • All tall people are good basketball players. Since he's tall, he must be a good basketball player.
  • He's tall, and all tall people are good basketball players. He must be a good basketball player.
  • He must be a good basketball player. After all, all tall people are good basketball players, and he's tall.
  • All tall people are good basketball players. He must be a good basketball player because he's tall.

In larger deductive arguments, especially the kind found in articles and essays, the conclusion will often be stated before any premises. But it's important to remember that the conclusion can appear anywhere in the argument. The key is to keep in mind what the argument as a whole is trying to prove.

One way to test that you've found the right conclusion is to use the "because" test. If you've chosen the right claim, you should be able to put because between it and all of the other premises. Thus:

He must be a good basketball player because he's tall and because all tall people are good basketball players.

Working with Arguments In Short

Unlike inductive arguments, which move from evidence to conclusion, deductive arguments move from the conclusion to evidence for that conclusion. The conclusion is the overall claim or main point of the argument, and the claims that support the conclusion are called premises. Deductive arguments can be supported by premises that work alone (separate support) or together (chain of support).

Skill Building until Next Time

  • When you hear an argument, ask yourself whether it is an inductive or deductive argument. Did the person move from evidence to conclusion, or conclusion to evidence? If the argument is too complex to analyze this way, try choosing just one part of the argument and see whether it's inductive or deductive.
  • When you come across deductive arguments today, try to separate the conclusion from the premises. Then consider whether the premises offer separate or chain support.

Exercises for this concept can be found at Inductive vs Deductive Reasoning Practice.

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