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    How to assess conditional arguments for validity

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    I need assistance to answer the following questions using syllogisms. Thank you.


    Hypothetical syllogisms (conditional arguments) can have two valid and two invalid structures. The two valid structures are affirming the antecedent (modus ponens) and denying the consequent (modus tollens). The two invalid structures, or fallacies, are denying the antecedent and affirming the consequent. Determine if the arguments below are valid or invalid and what form they take. The first one has been done for you.
    (NOTE: The term "modus pollens" has been used in some texts as a version of "modus ponens." For the purposes of this exercise, "modus ponens" will be used.)

    SAMPLE: Chris and Nick would be very happy if the Browns beat the Steelers. The Browns did beat the Steelers, so Chris and Nick are very happy, indeed.

    Valid Modus Ponens (Affirming the Antecedent)

    11. Madeline must have known the material for the test, because if a person knows the material, that person will get an A, and Madeline was one of the students that got an A.
    Madeline did get an A, Madeline did know the material. Valid

    12. Anastasia believes that if she treats people honestly and with an open mind, she will have diverse friendships. She is honest and open-minded and has friends all over the world.

    13. Roberto thought that if he worked very hard, his boss would give him a raise or a promotion. He made sure she noticed him, but she did not give him a raise or promotion. He thought he must not have worked hard enough.

    14. "I'm still eating too much ice cream," lamented George. "My waist measurement is the same as it was six months ago. I know if I didn't eat so much ice cream, I would reduce my waist size."

    15. The best way to make sure we pay fewer taxes is to elect conservatives. We must not have elected enough conservatives, because we are paying more taxes.

    16. If my neighbor were a decent human being, he wouldn't let his yard trash fall onto my property. But he's not a decent human being, so we get to clean his trash as well as ours.

    17. We'll have fun and learn a lot in this course, if we have great facilitator. We do have a great facilitator; therefore we are learning a lot and having fun doing it!

    18. If I could understand the concept of hypothetical syllogisms, I would get a passing grade. Hurray! I got a passing grade, so I must have understood the concept of hypothetical syllogisms.

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    Solution Summary

    Explains how to assess conditional arguments for validity. Illustrates the logical structure of valid conditional forms (modus ponens and modus tollens). Illustrates the logical structure of invalid conditional forms / deductive fallacies (denying the antecedent and affirming the consequent). Provides detailed explanations for how to evaluate two of the problems in this assignment as well as an answer key for all of the problems.