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Humanities Libertexts

2.8: Exercises

  • Page ID
    17951
  • Which of the following arguments are valid? Which are invalid?

    A

    1. Donna will get an A in philosophy if and only if she writes a good paper.

    2. Donna got an A in philosophy

    3. Therefore, she wrote a good paper.

    B

    1. If Donna writes a good paper, she will get an A in philosophy.

    2. Donna got an A in philosophy

    3. Therefore, she wrote a good paper.

    C

    1. If whales are mammals, then they are not fish.

    2. Whales are fish.

    3. Whales are not mammals.

    D

    1. If the rapture has occurred, then either some of the cars on the highway will be unoccupied or all drivers are damned.

    2. Some drivers are not damned.

    3. None of the cars on the highway are unoccupied.

    4. Therefore, the rapture has not occurred.

    E

    1. Some snarks are bandersnatches.

    2. All bandersnatches are igglypoofs.

    3. So, some snarks are igglypoofs

    Answer the following questions. Give short explanations that reason from the definitions of the relevant logical concepts.

    1. Does an argument provide a good reason for believing its conclusion if it is valid? Explain.

    2. Can a valid argument have a false conclusion? Explain.

    3. Can a sound argument have a false conclusion? Explain.

    4. What is it for a statement to be valid? (trick question)

    Which of the following arguments are inductively strong? Which are weak?

    1. It has rained every day in the Darién Gap for the past 25 years. Thus, it will probably rain in the Darién Gap tomorrow.

    2. People try on shoes before buying them. People drive cars before signing up for a three- year lease. People take a close look at travel information before committing to an expensive vacation. So, people should have sex with each other before committing to marriage.

    3. Two teenagers were found writing graffiti on the school walls yesterday. Thus, all teenagers are delinquents.

    4. A reliable study showed that 90 percent of Bellevue College’s students want more training in critical thinking. Maria is a student at Bellevue College. So, Maria probably wants more training in critical thinking.

    5. Upon landing at the SeaTac Airport, plane passengers saw broken buildings, large cracks in the runway, fire engines running about, and paramedics assisting injured people. The passengers concluded that an earthquake just occurred.

    Answer the following questions. Give short explanations based on the definitions of the relevant concepts.

    1. Explain how deductive validity and inductive strength differ.

    2. Can the conclusion of an inductively cogent argument be false? Explain.

    3. Must an inductively strong argument have true premises? Explain.

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