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Inductive/Deductive Reasoning

Inductive/Deductive Reasoning. Inductive Reasoning: Induction. Definition: reasoning out a general conclusion based on many specific cases/examples/experiences Reasoning from S PECIFIC to general. Example:

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Inductive/Deductive Reasoning

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  1. Inductive/Deductive Reasoning

  2. Inductive Reasoning: Induction Definition: reasoning out a general conclusion based on many specific cases/examples/experiences Reasoning from SPECIFIC to general

  3. Example: Jane dated a cowboy from Spanish Fork who was more interested in his truck than in her. She dated another cowboy from Spanish Fork who was more interested in his truck than in her. She dated a third cowboy from Spanish Fork who was also more interested in his truck than in dating her. Jane’s inductive conclusion: Cowboys from Spanish Fork are more interested in trucks than in girls.

  4. Caution in using induction • Sample (on which you base your conclusion) must be adequate. • Sample must be random. • The generalization mustonly cover only characteristics actually “proven” by the sample. LIMIT the conclusion!

  5. Polls • Conclusions from polls about what people support, etc. are inductive: the pollsters sample a scientifically derived number of random people to conclude what the city/state/nation/audience believes • Like all inductive conclusions, poll conclusions MUST be based on an adequate number of responses from random people • ANOTHER CAUTION: polls only tell people’s opinions, not whether something is true/false or good/bad

  6. Deductive Reasoning: Deduction Applying a proved, given generalization about a group (premise or assumption) to a member of the group Reasoning from GENERAL to specific

  7. Deduction: syllogisms • State the generalization about the group: major premise • Identify X as a member of the group: minor premise • Apply the generalization to X

  8. Examples • Deduction: I don’t like Jane because she is a nerd. • Syllogism: • Nerds are somehow undesireable/ negative. • Jane is a nerd. • Jane is undesireable/negative.

  9. Caution in Deduction: • Premises MUST BE TRUE. • Cannot do the reverse: because X has a characteristic of a group, he must be a member of that group.

  10. Rabbits jump high. • John jumps high. • John must be a rabbit.

  11. How such bad reasoning works: • She supports socialized medicine, so she must be a communist. • Syllogism: • Communists support socialized medicine. • She supports socialized medicine. • Therefore, she must be a communist.

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