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Logical Fallacies in Deductive Reasoning Practice

Updated on Sep 28, 2011

Review the lesson for Logical Fallacies in Deductive Reasoning Help.

Logical Fallacies in Deductive Reasoning Practice

Read the arguments below carefully. Do they use the ad hominem fallacy?

  1. Well, if that's what Harvey said, then it must be true.
  2. Well, he's got twenty years of experience dealing with consumer complaints, so I think we should trust his advice.
  3. He's good, but he's just not right for the job. After all, he's a Jets fan!
  4. Manager A to manager B: "I know we need to address the problem. But Caryn doesn't know what she's talking about. She's just a secretary."
  5. His opinion about her behavior is probably valid since he has known the woman his entire life.

Read the following arguments carefully. Do you see any red herrings? If so, underline them.

  1. Yes, I believe that it is time for rent laws to change, and here's why. It's very hard to pay my rent since my income is so low. How would you feel if you worked forty hours a week and could barely make ends meet? It's time for a change!
  2. It is wrong to censor the press. Our government has a law in the First Amendment that allows the press to express itself without interference or constraint by the government.
  3. Do you want to know why there are some people without healthcare? It's because too many politicians don't want to raise taxes because they are afraid they will lose votes.
  4. You should become a vegetarian. After all, do you know how many animals are on the verge of extinction?
  5. Marijuana should be legalized for certain medical conditions. Going blind from glaucoma is awful and it is unfair that people have to suffer like that. Cannabis greatly soothes the symptoms.

Do any of the following arguments use a straw man?

  1. All the union members want is to put us middle managers out of work.
  2. Lawyers don't really care about helping people. They're just out to make as much money as they can.
  3. LeeAnne feels that it's unwise for managers to have their own lounge because it reduces interaction with other employees and limits opportunities for spontaneous learning.
  4. Authors often do not want their books resold through used bookstores because it means they will not earn the royalties they get from the sale of new copies.

Answers

  1. Yes.
  2. No. His experience makes him credible, and that's a good reason to trust his advice.
  3. Yes.
  4. Yes. Just because she's a secretary and not a manager doesn't mean she doesn't have a good perspective on the problem. In fact, because she's "in the trenches," Caryn's ideas are probably very valuable to the managers.
  5. No. The time he has known this person makes the statement credible.
  6. Yes, I believe that it is time for rent laws to change, and here's why. It's very hard to pay my rent since my income is so low. How would you feel if you worked forty hours a week and could barely make ends meet? It's time for a change!
  7. It is wrong to censor the press. Our government has a law in the First Amendment that allows the press to express itself without interference or constraint by the government. (This argument provides relevant evidence for the conclusion.)
  8. Do you want to know why there are some people without healthcare? It's because too many politicians don't want to raise taxes because they are afraid they will lose votes.
  9. You should become a vegetarian. After all, do you know how many animals are on the verge of extinction? (True, vegetarians don't eat meat, but the kind of meat carnivores eat are not the animals that are on the verge of extinction. Instead of this red herring, this argument should give good reasons for giving up chicken, pork, beef, and the other types of meat common to the human diet.)
  10. Marijuana should be legalized for certain medical conditions. Going blind from glaucoma is awful and it is unfair that people have to suffer like that. Cannabis greatly soothes the symptoms.
  11. Yes. The middle managers misrepresent the position of the union members.
  12. Yes. This argument makes a sweeping generalization that misrepresents the position of all lawyers.
  13. No. This argument makes sense—LeeAnne's position is specific and clear.
  14. No. This argument makes sense and does not exaggerate, oversimplify, or misrepresent authors.
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