Comments:
: : : 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 : : : always get an A, and Madeline was one of the students : that : : : got an A. : : : : : : Valid Modius Ponens (Affirming the Antecedent) : : : : : : 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. : : : : : : Valid Modus Ponens (Affirming the Antecedent) : : : : : : 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. : : : : : : Valid Modus Tollens (denying the consequent) : : : : : : 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." : : : : : : INVALID Modus Tollens (denying the consequent) : : : : : : 15. The good 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. : : : : : : INVALID MOdus Tollens (denying the consequent) : : : : : : 16. If my neighbor were a decent human being, he : : wouldn't : : : let his tree leaves fall onto my property. But he's not : a : : : decent human being, so we get to clean his tree leaves : as : : : well as ours. : : : Invalid Modus Tollens : : : : : : : : : 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! : : : : : : Valid Modus Ponens (Affirming the Antecedent) : : : : : : 18. If I could only understand the concept of : : : hypothetical syllogisms, I would get an A in class. : : Hurray! : : : I got an A in class, so I must have understood the : concept : : : of hypothetical syllogisms. : Valid Modus Ponens

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