Introduction to inductive and deductive reasoning

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Introduction to inductive and deductive reasoning

  1. 1. Introduction to Inductive and Deductive Reasoning English 1A Renee Bangerter
  2. 2. Inductive Reasoning <ul><li>Specific General </li></ul>
  3. 3. Inductive Reasoning <ul><li>Induction reasons from evidence about some members of a class in order to form a conclusion about all members of a class. </li></ul><ul><li>A conclusion derived through inductive reasoning is called a hypothesis and is always less certain than the evidence itself. In other words, the conclusion is probable . </li></ul>
  4. 4. Inductive Reasoning <ul><li>Induction can be done through the following: </li></ul><ul><ul><li>Observation </li></ul></ul><ul><ul><li>Number Sampling </li></ul></ul><ul><ul><li>Analogical Reasoning </li></ul></ul><ul><ul><li>Pattern Recognition </li></ul></ul><ul><ul><li>Causal Reasoning </li></ul></ul><ul><ul><li>Statistical Reasoning </li></ul></ul>
  5. 5. Inductive Reasoning <ul><li>Inductive reasoning is used when examining all data would be an impossible task. In this case, induction uses statistical samplings. </li></ul>
  6. 6. Inductive Example <ul><li>Evidence: Samantha took Renee Bangerter’s English 1A and got an A. </li></ul><ul><li>Evidence: John took her English 1A and got an A. </li></ul><ul><li>Evidence: I also know that Mike took her 1A class and got an A. </li></ul><ul><li>Conclusion: If I take Renee Bangerter’s English 1A, I’ll get an A, too. </li></ul>
  7. 7. You Try… “ Now let’s see—one sashweight, one butcher’s cleaver, on galvanized-iron tub, fifty feet of half-inch rope, one gunny sack, one electric torch, one pickaxe, one shovel, twenty pounds of quicklime, a box of cigars, and a beach chair.” Drawing by Chas. Addams The New Yorker Magazine From the Critical Eye by Sally Taylor, 1990
  8. 8. Deductive Reasoning <ul><li>General Specific </li></ul>
  9. 9. Deductive Syllogism <ul><li>Syllogism: An argument arranged in three parts </li></ul><ul><ul><li>Major Premise: General Principle </li></ul></ul><ul><ul><li>Minor Premise: Specific Instance </li></ul></ul><ul><ul><li>Conclusion: Follows Logically </li></ul></ul><ul><ul><li>Standard, everyday language is arranged into verbal equations </li></ul></ul>
  10. 10. Syllogisms <ul><li>Major Premise : All men are mortal (general principle) </li></ul><ul><li>Minor Premise : Socrates is man (specific instance) </li></ul><ul><li>Conclusion : Socrates is mortal (follows logically from the major) </li></ul><ul><li>Valid Argument: The conclusion follows logically from the major and minor premise. </li></ul>
  11. 11. Practice with Syllogisms <ul><li>Major Premise: Stealing is a criminal act. </li></ul><ul><li>Minor Premise: Shoplifting is stealing. </li></ul><ul><li>Conclusion: Therefore? </li></ul><ul><li>Shoplifting is a criminal act. </li></ul><ul><li>Notice: A claim of definition </li></ul><ul><li>is a form of syllogism. </li></ul>
  12. 12. Valid and Invalid Syllogisms <ul><li>Major Premise: When Gabriele drinks coffee she always gets a headache. (Fact?) </li></ul><ul><li>Minor Premise: Gabriele is drinking coffee. </li></ul><ul><li>(Fact?) </li></ul><ul><li>Conclusion: Gabriele will get a headache. </li></ul><ul><li>Valid or invalid? </li></ul>
  13. 13. Valid and Invalid Syllogisms <ul><li>Major Premise: When Gabriele drinks coffee she always gets a headache. </li></ul><ul><li>Minor Premise: Gabriele has a headache. </li></ul><ul><li>(Fact?) </li></ul><ul><li>Conclusion: Therefore? </li></ul><ul><li>Gabriele drank coffee. </li></ul><ul><li>Valid or Invalid? </li></ul><ul><li>True? </li></ul>
  14. 14. Valid versus True <ul><li>Valid: the conclusion follows logically from the major and minor premise. </li></ul><ul><li>Keep in mind—While we use the term “valid” in everyday speech, it has a very specific meaning in logic. </li></ul><ul><li>True: Corresponds to reality, believable, provable. </li></ul><ul><li>Sound: both valid and true. </li></ul>
  15. 15. What Do You Think? <ul><li>Major Premise: Drug dealers wear electronic pagers. </li></ul><ul><li>Minor Premise: Doctors wear electronic pagers. </li></ul><ul><li>Conclusion: Therefore? </li></ul><ul><li>Therefore Doctors are drug dealers. </li></ul><ul><li>Valid or Invalid? True? Sound? </li></ul><ul><li>Logical Fallacy: Guilt by association. </li></ul>
  16. 16. Complete the Syllogism <ul><li>All Italians are volatile. </li></ul><ul><li>Jesse is Italian. </li></ul><ul><li>Therefore: </li></ul><ul><ul><ul><li>Jesse is volatile </li></ul></ul></ul><ul><li>Valid? </li></ul><ul><li>True? </li></ul><ul><li>Sound? </li></ul><ul><li>This syllogism is based on a hasty generalization. Therefore, it is not sound. </li></ul>
  17. 17. Complete the Syllogism <ul><li>All kids who wear Abercrombie and Fitch to school will be accepted by the popular group. </li></ul><ul><li>Adrienne wears Abercrombie and Fitch to school. </li></ul><ul><li>Therefore? </li></ul><ul><ul><ul><li>She will be accepted by the school’s popular group. </li></ul></ul></ul><ul><li>Valid? </li></ul><ul><li>True? </li></ul><ul><li>Sound? </li></ul>
  18. 18. Enthymeme <ul><li>An argument in which the major premise is left unstated </li></ul><ul><li>(often a conclusion supported by a single premise ). </li></ul><ul><li>She must be a good student since she is on the Dean’s List. </li></ul><ul><li>Conclusion Minor Premise </li></ul><ul><li>She must be a good student since she is on the Dean’s List. </li></ul><ul><li>Major Premise? </li></ul><ul><li>All good students are on the Dean’s List. </li></ul>
  19. 19. Examples of Enthymemes <ul><li>Alcoholic beverages destroy brain cells, so alcohol should be made illegal. </li></ul><ul><li>You are all good students because you have your homework done on time. </li></ul>Recreate the Syllogism

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