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Inductive v. deductive

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A very detailed look at inductive vs. deductive reasoning.

Text of Inductive v. deductive

  • 1. Inductive vs.Deductive Reasoning

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. 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. Deductive Reasoning 5. Deductive ReasoningFrom vagueTo specific 6. A deductive argument is one in which it is impossible for the premises tobe true but the conclusion false. It is supposed to be a definitive proof of the truth ofthe 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 simplyisnt possible for the conclusion to be false. If you have a deductive argument and you acceptthe truth of the premises, then you must also acceptthe truth of the conclusion. 7. A deductive argument TrueTrue TruePremise Premise Conclusion 8. Deductive Reasoning Example: Smithowns 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. Inductive Reasoning The process of going fromobservations to conclusions. This type of conclusion issometimes called an inference. 10. Inductive Reasoning Observingthat something is truemany times, then concluding thatit will be true in all instances Using the data to make aprediction 11. Inductive Reasoning 12. Inductive Reasoning From specificTo vague 13. An inductive argument is one in which the premises are supposed to support theconclusion. If the premises are true, it is unlikely that the conclusionis 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 theconclusion to be false (maybe Socrates was allergic tofish). Words which tend to mark an argument as inductiveinclude probably, likely, possibly and reasonably. 14. A inductive argument TrueTrue ProbablyPremise Premise TrueConclusion 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. 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 companys 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. Lets Practice The word wall is Inductive The windows are Deductive 18. #1 Premise: Conclusion:Everything madeThis wire willof copperconductconducts electricity.electricity. Premise:This wire is madeof copper. 19. #2 Premise: Conclusion:Socrates Socrateswas Greek. probably ate Premise: fish.Most Greekseat fish. 20. #3 The local branch of Wachovia Bank wasrobbed yesterday. Jenny needed moneyto pay off her gambling debts. She justbought a gun two days ago, and I sawher hanging around the local WachoviaBank yesterday morning. Today thebookies goons stopped looking forJenny. So Jenny robbed WachoviaBank yesterday. 21. #4 Premise:All Conclusion: Iturtles have conclude thatshells.the animal in Premise: The my bag has aanimal I haveshell.captured is aturtle. 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. #6 Premise: Tonya is Conclusion:seen walking from Tonya hasher car to her homebought the set ofwith a set of golfclubs.golf clubs for Premise: TonyasJack.husband Jeff lovesgolf and tomorrowis his birthday.

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