Evaluating deductive reasoning and fallacies

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  • Grammatically Equivalent Structures
  • Evaluating deductive reasoning and fallacies

    1. 1. Chapter 8 Evaluate Deductive Reasoning and Spot Deductive Fallacies
    2. 2. Deductive Validity and Language • An argument is deductively valid if there is no possibility, real or imaginable: – Short of changing the very meanings of the terms and the rules of grammar: – That will make the premises all true and the conclusion false© 2013 Pearson Education, Inc. All
    3. 3. Deductive Validity and Language • Certain configurations of language form deductively valid argument templates • Without violating the meanings of the words/grammatical rules of the language: – There is no possible way for the premises all to be true and the conclusion false© 2013 Pearson Education, Inc. All
    4. 4. Deductive Validity and Language • Reasoning Deductively about Declarative Statements – Denying the Consequent – Affirming the Antecedent – Disjunctive Syllogism – Neither, Unless, and Only© 2013 Pearson Education, Inc. All
    5. 5. Deductive Validity and Language • Reasoning Deductively about Classes of Objects – Applying a Generalization – Applying an Exception – The Power of Only • One of the most interesting words in the language:© 2013 Pearson Education, Inc. All
    6. 6. Deductive Validity and Language – Only has the power to change the meaning of a sentence depending on where it is placed • Classes and Objects • Reasoning Deductively about Relationships – Natural languages are rich with terms that describe relationships© 2013 Pearson Education, Inc. All
    7. 7. Deductive Validity and Language – Our understanding of the logical implications of relational terms is part of: • Our comprehension of language – Transitivity, Reflexivity, and Identity • Transitivity Relationship • Reflexivity Relationship • Identity Relationship© 2013 Pearson Education, Inc. All
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    11. 11. Fallacies Masquerading as Valid Deductive Arguments • Just as there are valid argument templates there are fallacious argument templates • Precision of thought and expression is the key to avoiding these mistakes in: – Our own argument making and also in our evaluation of the arguments offered to us© 2013 Pearson Education, Inc. All
    12. 12. Fallacies Masquerading as Valid Deductive Arguments • Fallacies When Reasoning with Declarative Statements – Affirming the Consequent – Denying the Antecedent – The House M.D. Fallacy • Fallacies When Reasoning about Classes of Objects© 2013 Pearson Education, Inc. All
    13. 13. Fallacies Masquerading as Valid Deductive Arguments – There are logically correct ways of reasoning about classes of objects & their members: • There are familiar mistakes we often hear being made – False Classification • Examples of False Classification seem remarkably abundant© 2013 Pearson Education, Inc. All
    14. 14. Fallacies Masquerading as Valid Deductive Arguments – Fallacies of Composition and Division • Reasoning about the relationships of parts and wholes can appear to be deductively valid: – But fail because the attribute that applies to the parts may not apply to the whole, or vice versa – Mistaken Identity© 2013 Pearson Education, Inc. All
    15. 15. Fallacies Masquerading as Valid Deductive Arguments • Fallacies that occur when reasoning about relationships like identity, reflexivity, or transitivity: – Most often occur when people think they are talking about the same thing, but in fact are not – False Reference – Create Your Own Deductive Reasoning Examples© 2013 Pearson Education, Inc. All

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