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3.4 Fallacies in Logic

3.4 Fallacies in Logic
  • Math Help

    In logic, the premise

    If P, then Q


    is logically equivalent to its contrapositive

    If not Q, then not P.


    The contrapositive, however, is not what is involved in denying the antecedent.

    Premise: When it rains, the ground gets wet. If P, then Q.
    Premise: It isn't raining. Not P.
    Conclusion: Therefore, the ground is not wet. Therefore, not Q.

    Do you see why the type of fallacy is called denying the antecedent?

  • Consumer Suggestion

    A “lemon” is referred to as a new car that repeatedly fails to meet standards of quality and performance. “Lemon law” is the common name for the laws that help consumers if a new car fails and the manufacturer does not honor the warranty.

    Visit Lemon Law America to see the lemon laws for your state. You can also see a new car guide for buying tips if you are looking to purchase a new car.

  • Checkpoint Solution

    Here is the original statement.

    The buyer of a new vehicle brought claims against a manufacturer under Ohio's Lemon Law and for breaches of a warranty act. The trial court ruled in favor of the defendant on both claims. The court of appeals analyzed the trial court's logic. The trial court first addressed the plaintiff's Lemon Law claim and determined that it was invalid. Next, the trial court concluded that since the Lemon Law claim was not valid, the warranty act claim was not valid. The court of appeals rejected the trial court's reasoning, based on the fallacy of denying the antecedent.

    Summarized from "Conventional Logic: Using the Logical Fallacy of Denying the Antecedent as a Litigation Tool," Stephen Rice

    Here is a possible rewriting as a syllogism.

    Premise: If the Lemon Law claim is valid, then the automobile warranty is valid.
    Premise: The Lemon Law claim is not valid.
    Conclusion: Therefore, the automobile warranty is not valid.

    In this form, you can see that the syllogism is a fallacy and that it is of the form denying the antecedent.

  • Comments (3)

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    system user
    Guest   1 decade ago |
    I like this chapter on logic, especially the examples on fallacies. I wish more people in our government studied logic.
    system user
    Guest   1 decade ago |
    2012 is the 100th anniversary of Turing's birth. To recognize and honor Turing's life and work, 2012 has been designated at "Alan Turning Year" Events are scheduled in many countries around the world including the USA, Brazil, China, Czech Republic, the Philippines, New Zealand, Israel, Spain, Norway, Italy, Portugal and Germany. The keystone events will be a three-day conference in Manchester, UK in June examining Turing's mathematical and code-breaking achievements, and a Turing Centenary Conference in Cambridge organized by King's College,
    system user
    Ron Larson (author)1 decade ago |
    In spite of his contributions in World War II, the British government prosecuted Alan Turning and convicted him of indecency. It took over 60 years, long after his death, for the government to issue an apology for his treatment.