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Reason

“Logic is the beginning of wisdom, Valeris , not the end.” Mr. Spock, Star Trek. Reason. Logic is the branch of philosophy that explores the way we reason. It attempts to Define “correct” reasoning. Distinguish good arguments from bad ones. Pick out flaws and weaknesses in reasoning.

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Reason

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  1. “Logic is the beginning of wisdom, Valeris, not the end.” Mr. Spock, Star Trek Reason

  2. Logic is the branch of philosophy that explores the way we reason. It attempts to • Define “correct” reasoning. • Distinguish good arguments from bad ones. • Pick out flaws and weaknesses in reasoning. • Create rules which enable us to test whether our reasoning is coherent and consistent. Reason Vs. Logic

  3. In logic an argument is not a dispute between two people, an argument states reasons for a conclusion. • Example: I have to turn my homework in on Monday. Today is Friday. I don’t have time to do my homework on Saturday or Sunday. I must do my homework on Friday night. Argument

  4. Another Argument

  5. i.e. Syllogisms • Premise: The information you have been given in an argument. • Conclusion: The position reached at the end of the argument. • Premise 1: Penguins are black and white • Premise 2: Some old tv shows are black and white • Conclusion: Therefore, some penguins are old tv shows. Argument in Two Parts

  6. A deductive argument is any type of reasoning that moves from the general to the specific. Deductive Logic General P1: All dogs are mammals. P2: Fido is a dog. Con: Therefore, Fido is a mammal. P1: Only boys have XY chromosomes. P2: Karl has an XY chromosome. Con: Therefore, Karl is a boy. Specific

  7. An inductive argument moves from specific reasons to more general ones. Inductive Logic Specific P1: Fido is a mammal. P2: Fido is a dog. Con: Therefore, dogs are mammals. P1: Karl is a boy P2: Karl has an XY chromosome. Con: Therefore, boys have XY chromosomes. General

  8. Italians eat spaghetti. • Giovanni eats spaghetti. • Therefore, Giovanni is Italian. • Andrea and Katie like boys. • Katie and Andrea are girls. • All girls like boys. Practice

  9. When a conclusion follows from the premises it is valid, but not necessarily true. When a conclusion does not follow from the premises it is invalid, but may be true. Valid and invalid just refer to whether the reasoning is correct. Valid vs. Invalid

  10. An argument is sound if • It’s a valid argument (the conclusion must follow from the premises) and • The premises are true. Sound Arguments

  11. Valid, invalid, sound • All men like the color blue. • Rob has a blue shirt. • All men will like Rob’s shirt. • All men are mortal. • Socrates is a man. • Therefore, Socrates is mortal. Practice

  12. Practice All fire-breathing rabbits live on Mars All humans are fire-breathing rabbits Therefore, all humans live on Mars My 4th period consists of students My 4th period annoys me Therefore, some students annoy me

  13. Practice writing some valid, sound arguments. • Write 5 syllogisms that are valid but not sound. • Write 5 more syllogisms that are valid and sound. Practice

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