Inductive v. deductive


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A very detailed look at inductive vs. deductive reasoning.

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Inductive v. deductive

  1. 1. Inductive vs. Deductive Reasoning
  2. 2. Deductive Reasoning Startswith a general rule (a premise) which we know to be true. Then, from that rule, we make a true conclusion about something specific.
  3. 3. Deductive Reasoning The process of reasoning from known facts to conclusions. When you reason deductively, you can say “therefore” with certainty. If your facts were firm to begin with, then your conclusions will also be firm.
  4. 4. Deductive Reasoning
  5. 5. Deductive Reasoning From vague To specific
  6. 6. A deductive argument is one in which it is impossible for the premises to be true but the conclusion false. It is supposed to be a definitive proof of the truth of the claim (conclusion).  Premise  All men are mortal.  Premise  Socrates was a man.  Conclusion  Socrates was mortal. If the premises are true (and they are), then it simply isnt possible for the conclusion to be false. If you have a deductive argument and you accept the truth of the premises, then you must also accept the truth of the conclusion.
  7. 7. A deductive argument True True TruePremise Premise Conclusion
  8. 8. Deductive Reasoning Example:  Smith owns only blue pants and brown pants. Smith is wearing a pair of pants today. So, Smith is wearing either blue or brown pants today.
  9. 9. Inductive Reasoning The process of going from observations to conclusions. This type of conclusion is sometimes called an inference.
  10. 10. Inductive Reasoning Observing that something is true many times, then concluding that it will be true in all instances Using the data to make a prediction
  11. 11. Inductive Reasoning
  12. 12. Inductive Reasoning From specific To vague
  13. 13. An inductive argument is one in which the premises are supposed to support the conclusion. If the premises are true, it is unlikely that the conclusion is false. The conclusion probably follows from the premises.  Premise  Socrates was Greek.  Premise  Most Greeks eat fish.  Conclusion  Socrates ate fish. Even if both premises are true, it is still possible for the conclusion to be false (maybe Socrates was allergic to fish). Words which tend to mark an argument as inductive include probably, likely, possibly and reasonably.
  14. 14. A inductive argument True True ProbablyPremise Premise True Conclusion
  15. 15. Inductive Reasoning Example:  January has been cold here in Siberia. Today is January 14, so it is going to be another cold day in Siberia.
  16. 16. Which conclusion below shows evidence of deductive reasoning?A. One time an employee used store computers to download a harmful virus, so employee computer use is a security threat.B. Many customers complained about employees using computers rather than working, so computer misuse was harming the company’s sales.C. An employee on a break distracted other employees by using a computer in a public area for private business, so that employee was given a warning.D. Several employees left customer sales information visible on computer screens, so those employees were instructed to always close windows with personal information.
  17. 17. Let’s Practice – The word wall is Inductive The windows are Deductive
  18. 18. #1 Premise:  Conclusion: Everything made This wire will of copper conduct conducts electricity. electricity. Premise: This wire is made of copper.
  19. 19. #2 Premise:  Conclusion: Socrates Socrates was Greek. probably ate Premise: fish. Most Greeks eat fish.
  20. 20. #3 The local branch of Wachovia Bank was robbed yesterday. Jenny needed money to pay off her gambling debts. She just bought a gun two days ago, and I saw her hanging around the local Wachovia Bank yesterday morning. Today the bookie’s goons stopped looking for Jenny. So Jenny robbed Wachovia Bank yesterday.
  21. 21. #4 Premise: All  Conclusion: I turtles have conclude that shells. the animal in Premise: The my bag has a animal I have shell. captured is a turtle.
  22. 22. #5Sherlock Holmes and Watson were on acamping trip. They had gone to bed and werelying there looking up at the sky. Holmes said,“Watson, look up. What do you see?”“I see thousand of stars.”“And what does that mean to you?”“I guess it means we will have another niceday tomorrow. What does it mean to you,Holmes?”“To me, it means someone has stolen ourtent.”
  23. 23. #6 Premise: Tonya is  Conclusion: seen walking from Tonya has her car to her home bought the set of with a set of golf clubs. golf clubs for Premise: Tonya’s Jack. husband Jeff loves golf and tomorrow is his birthday.