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Ch. 4 DEDUCTIVE ARGUMENT

Ch. 4 DEDUCTIVE ARGUMENT. Reasoning from the General to the Specific. Deductive Argument. A specific conclusion is inferred from a series of generalized statements. Conclusions are usually indisputable. vs. Inductive Argument (ch3).

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Ch. 4 DEDUCTIVE ARGUMENT

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  1. Ch. 4DEDUCTIVE ARGUMENT Reasoning from the General to the Specific

  2. Deductive Argument • A specific conclusion is inferred from a series of generalized statements. • Conclusions are usually indisputable

  3. vs. Inductive Argument (ch3) • A general conclusion was inferred from several pieces of information • Conclusions could contain factors of uncertainty

  4. Syllogism • The most common way of presenting a deductive argument (not found in inductive arguments) • Contains a major premise, a minor premise, and a conclusion

  5. Categorical Syllogism (Valid) • Major Premise All A is B. • Minor Premise C is A, • Conclusion C is B.

  6. Categorical Syllogism example MAJ: All students in Critical Thinking are nice. A is/are B) MIN: Katie is a student in Critical Thinking. (C is A) CON: Katie is nice. (C is B)

  7. Another way of looking at it.

  8. Another example Major Premise: All WHS students (A) are to be in class at 7:25 AM (B). Minor Premise: Josh (C) is a WHS student (A). Conclusion: Josh (C) is be in class at 7:25 AM (B).

  9. What would the diagram look like?

  10. Answer

  11. Notice the difference in this one • Major Premise: *Most people between the ages of 16 and 18 (A) are students (B) • Minor Premise: Christina (C) is 18 years old (A) • Conclusion: Christina (C) is *probably a student (B). *be aware of overstatement

  12. The diagram • The diagram must change to reflect the syllogism correctly. B. Students A. 16-18 yr olds (remember most, not all) C. Christina

  13. Incorrect/Untruthful Conclusion • Major Premise: All students (A) are lazy, ignorant individuals (B). • Minor Premise: Ryan (C) is a student (A) • Conclusion: Ryan (C) is a lazy and ignorant individual (B) • Valid in form, but false premise.

  14. Incorrect/Untruthful Conclusion • Appears valid in form; however, incorrect conclusion. • False major premise

  15. Incorrect/Untruthful Conclusion • If the premise(s) is false, the conclusion will be untrue. • Use the Tests of Evidence from ch. 2 to determine the truth of the premises. • Sufficient evidence? • Evidence deliberately omitted? • Conflict with other evidence? • Relevant evidence? • Accurately reported evidence?

  16. INVALID Categorical Syllogisms • Major Premise: All A is B. • Minor Premise: C is B. • Conclusion: C is A. • Invalid in form

  17. INVALID example • Major Premise: All basketball players (A) are good runners (B). • Minor Premise: Mike (C) is a good runner (B). • Conclusion: Mike (C) is a basketball player (A).

  18. The Diagram Mike is a good runner, but that doesn’t mean he is a b-ball player. A. BB Players B. Good runners C. Mike

  19. Enthymeme • A Catagorical syllogism with an unstated premise • contains conclusion • Missing a premise • Note: Enthymemes are always considered valid!!

  20. Enthymeme example • These jeans are sure to be in style because they were purchased from the Gap. • Major Premise (unstated): Most jeans purchased from the Gap are in style. • Minor Premise: These jeans were purchased from the Gap. • Conclusion: These jeans are (probably) in style.

  21. In Conclusion: Differences between inductive & deductive reasoning • Arguments using inductive reasoning go from specific to general, and it is difficult to arrive at an indisputable conclusion. • Deductive reasoning can produce logical conclusions if (a) the syllogism is correctly structured. (b)the premises satisfy the Tests of Evidence

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