Logic Unit Notes


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Notes on philosophers, logic and logical fallacies.

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Logic Unit Notes

  1. 1. Who Defined the Study of Philosophy and Logic? <ul><li>Socrates, Plato and Aristotle </li></ul><ul><li>These three philosophers form the basis of what is known as Western Philosophy </li></ul><ul><li>Every thinker and scientist that followed used their methods </li></ul>
  2. 2. Socrates b. 470 BCE <ul><li>Developed the Socratic method: </li></ul><ul><ul><ul><li>A series of questions are used to </li></ul></ul></ul><ul><ul><ul><li>examine beliefs and develop ideas . </li></ul></ul></ul><ul><li>“ The unexamined life is not worth living.” </li></ul><ul><li>“ There is only one good, knowledge , and one evil, ignorance .” </li></ul><ul><li>“ Know thyself .” </li></ul><ul><li>Was executed in Athens after being convicted of corrupting the youth with his ideas. </li></ul>
  3. 3. Plato b. 428 BCE <ul><li>Was Socrates’ brilliant student </li></ul><ul><li>Traveled extensively before returning to teach at The Academy. </li></ul><ul><li>Allegory of the Cave- the real world is only a reflection of the truth, of a higher reality </li></ul><ul><li>He believed that the perfect political system would feature “ philosopher kings ” as it rulers, people versed in ethics and who truly loved only one thing: truth and knowledge </li></ul>
  4. 4. Aristotle b. 384 BCE <ul><li>Plato’s student </li></ul><ul><li>Aristotle studied almost every single topic from anatomy to economics to geography, physics, politics, psychology, religion, and even poetry. </li></ul><ul><li>He founded his own school after leaving the Academy, and his center of knowledge became known as the Lyceum . </li></ul><ul><li>Was Alexander the Great’s personal teacher. </li></ul>
  5. 5. Aristotle Part 2 <ul><li>Developed a vast system of rules for logical thinking to define the world. </li></ul><ul><li>Much like a game has rules, so, too, must logic </li></ul><ul><li>Syllogism def. If A=B and B=C, then A=C </li></ul><ul><li>Causality: If I set fire to a piece of paper ( cause ) then it will burn ( effect ). </li></ul><ul><li>Scientific Method: </li></ul><ul><ul><ul><li>1. Observe and take notes </li></ul></ul></ul><ul><ul><ul><li>2. Make a theory </li></ul></ul></ul><ul><ul><ul><li>3. Test the theory </li></ul></ul></ul>
  6. 6. What is Logic? <ul><li>Def. logic is the study of the rules for correct, or valid, reasoning . </li></ul><ul><li>Deduction : Reasoning that moves from the general to the specific . It is a form of inference where if the premises are true , the conclusion must also be true . </li></ul><ul><ul><li>All humans have two legs, the major premise, </li></ul></ul><ul><ul><li>I am a human, the minor premise, therefore, </li></ul></ul><ul><ul><li>I have two legs , the conclusion. </li></ul></ul><ul><li>Induction : Reasoning that typically moves from specific examples to a larger, general observation. If the premises are true , it is improbable that the conclusion is false. </li></ul><ul><ul><ul><ul><li>'95 households out of 100 have a TV. I am going to stay with Fred, so I will probably be able to watch TV&quot;. </li></ul></ul></ul></ul>
  7. 7. Quick check: Stop taking notes! <ul><li>I failed that course because the instructor didn’t like me. </li></ul><ul><ul><li>Assumption : The instructor fails students he doesn’t like. </li></ul></ul><ul><li>I’m not surprised he made the team. After all, his father is the superintendent of schools. </li></ul><ul><ul><li>Assumption : The superintendent gives special favors to his family </li></ul></ul><ul><li>If I’d only taken my boss to lunch more often, I could have gotten that raise. </li></ul><ul><ul><li>Assumption : The boss denies raises to people who don’t take him to lunch very often. </li></ul></ul><ul><ul><li>Analyze the assumptions behind every idea!!! </li></ul></ul>What are the unstated assumptions?
  8. 8. What is a syllogism? <ul><li>a specific method of logical deduction (moving from the general to the particular) every syllogism contains at least three parts: </li></ul><ul><ul><li>a major premise (global assumption) </li></ul></ul><ul><ul><li>a minor premise (specific claim) </li></ul></ul><ul><ul><li>a conclusion </li></ul></ul><ul><li>It’s kind of like simple math </li></ul>If A = B and B = C, then A = C
  9. 9. A visual representation Fish are not mammals Not in your notes -- just think it through! all things with hair all mammals have hair mammals fish do not have hair fish
  10. 10. True vs. Valid Arguments <ul><li>True argument = an argument with a conclusion that is considered factually correct . </li></ul><ul><li>Valid argument = an argument with a conclusion that makes sense logically , regardless of whether it is true or not . </li></ul>
  11. 11. True, Valid or Both? bad drivers All old people are bad drivers. Old people Jean is an old person. Jean Jean is a bad driver. If the premises are true, the conclusion would be true. So this is a valid argument , but obviously false.
  12. 12. True, Valid, or Both <ul><li>All fruits have seeds. </li></ul><ul><li>Tomatoes have seeds. </li></ul><ul><li>Therefore, a tomato is a fruit. </li></ul>Scientifically, this is valid and true All fruits Tomatoes
  13. 13. Is this True, Valid, or Both? <ul><li>No human being is immortal. </li></ul><ul><li>Ghosts are not human beings. </li></ul><ul><li>Therefore, ghosts are immortal. </li></ul>Faulty logic because this syllogism assumes anything not human is immortal. However, according to some people’s beliefs, this is a true statement: So this is an invalid argument, but a true conclusion. ghosts all things immortal human beings
  14. 14. Is this True, Valid, or Both? <ul><li>All weeds are plants. </li></ul><ul><li>A flower is a plant. </li></ul><ul><li>Therefore, all weeds are flowers. </li></ul>weeds flowers The conclusion here does not logically follow as a necessary consequence; therefore this argument is invalid . plants