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P160 Duhem and Quine

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P160 Duhem and Quine

  1. 1. PHIL 160 “Duhem, Quine, and Challenges in Theory Testing” PHIL 160
  2. 2. LEARNING OBJECTIVES: PHIL 160 Underdetermination of theory by data
  3. 3. LEARNING OBJECTIVES: PHIL 160 Underdetermination of theory by data Holism in testing
  4. 4. LEARNING OBJECTIVES: PHIL 160 Underdetermination of theory by data Holism in testing Meaning holism
  5. 5. THEORY • What kind of stuff is in the world • How that stuff behaves PHIL 160
  6. 6. PHIL 160 INDUCTIVE LOGIC Narrow Inductivist Picture of Science: Collect data from experience Derive generalizations
  7. 7. PHIL 160 Form hypotheses Hempel’s Picture of Science: <ul><li>Find test implications. </li></ul><ul><li>Set up test conditions. </li></ul><ul><li>See what happens. </li></ul>Test hypotheses (data + imagination )
  8. 8. PHIL 160 <ul><li>If H is true, will observe I under test conditions. </li></ul><ul><li>Set up test conditions. </li></ul><ul><li>Observe not-I. </li></ul><ul><li> H is false </li></ul>Test hypotheses - negative test
  9. 9. PHIL 160 Problem of induction <ul><li>If H is true, will observe I under test conditions. </li></ul><ul><li>Set up test conditions. </li></ul><ul><li>Observe not-I. </li></ul><ul><li> H is false </li></ul>Test hypotheses - negative test
  10. 10. PHIL 160
  11. 11. PHIL 160
  12. 12. PHIL 160
  13. 13. PHIL 160 scientific theories underdetermined by experience
  14. 14. PHIL 160
  15. 15. PHIL 160
  16. 16. PHIL 160
  17. 17. PHIL 160 <ul><li>If H 1 and H 2 and H 3 and H 4 and … are true, will observe I under test conditions. </li></ul><ul><li>Set up test conditions. </li></ul><ul><li>Observe not-I. </li></ul><ul><li> H 1 or H 2 or H 3 or H 4 or … is false </li></ul>Test group of hypotheses
  18. 18. PHIL 160 Individual hypotheses don’t always generate testable predictions. H1: “Cadaveric matter causes childbed fever.”
  19. 19. PHIL 160
  20. 20. PHIL 160 Need auxiliary hypotheses to generate testable predictions: H1: Cadaveric matter causes childbed fever. H2: Cadaveric matter is transferred from cadavers to patients via hands, instruments. H3: Washing hands, instruments in chlorinated lime will remove or destroy cadaveric matter.
  21. 21. PHIL 160
  22. 22. PHIL 160 Negative test - Test group of hypotheses
  23. 23. PHIL 160 Negative test - there is a problem SOMEWHERE in the group of hypotheses Test group of hypotheses
  24. 24. PHIL 160 Some individual hypotheses are testable: H: Mars has a triangular orbit.
  25. 25. PHIL 160
  26. 26. PHIL 160 1 st law of motion : If there is no force acting on a body, the momentum of that body will remain constant. Newton’s group of hypotheses
  27. 27. PHIL 160 2 nd law of motion : If there is a force acting on a body, that body will accelerate by an amount directly proportional to the strength of the force and inversely proportional to its mass. Newton’s group of hypotheses
  28. 28. PHIL 160 3 rd law of motion : If one body exerts a force on a second body, then the second body exerts a force on the first body that is equal in strength and opposite in direction. Newton’s group of hypotheses
  29. 29. PHIL 160 Law of universal gravitation : Any two bodies exert attractive forces on each other where the forces are in the direction of the line connecting the bodies and are proportional to the product of their masses divided by the square of the distance between them. Newton’s group of hypotheses
  30. 30. PHIL 160 3 laws of motion + law of universal gravitation No testable predictions! Newton’s group of hypotheses
  31. 31. PHIL 160 3 laws of motion + law of universal gravitation + auxiliary hypotheses about masses, positions of planets and sun Predictions of planets’ orbits Newton’s group of hypotheses
  32. 32. PHIL 160 But where? Negative test - there is a problem SOMEWHERE in the group of hypotheses Test group of hypotheses
  33. 33. PHIL 160 Bad prediction of Uranus’s orbit 3 laws of motion + law of universal gravitation + auxiliary hypotheses about masses, positions of planets and sun Newton’s group of hypotheses
  34. 34. PHIL 160 Bad prediction of Uranus’s orbit 3 laws of motion + law of universal gravitation + auxiliary hypotheses about masses, positions of planets and sun Missing a planet? Newton’s group of hypotheses
  35. 35. PHIL 160
  36. 36. PHIL 160 Astronomers changed auxiliary hypothesis about how many planets, left Newton’s laws & UG unchanged. This fixed bad prediction of Uranus orbit. New planet (Neptune) observed by telescope.
  37. 37. PHIL 160
  38. 38. 3 laws of motion + law of universal gravitation + auxiliary hypotheses about masses, positions of planets and sun PHIL 160 Bad prediction of Mercury’s orbit Newton’s group of hypotheses
  39. 39. PHIL 160 First attempt: stick another planet in (“Vulcan”) between Mercury and Sun.
  40. 40. PHIL 160 No repeatable observations of this new planet. First attempt: stick another planet in (“Vulcan”) between Mercury and Sun.
  41. 41. PHIL 160 No repeatable observations of this new planet. (Possible aux. hypothesis: the new planet is invisible!) First attempt: stick another planet in (“Vulcan”) between Mercury and Sun.
  42. 42. 3 laws of motion + law of universal gravitation + auxiliary hypotheses about masses, positions of planets and sun PHIL 160 Bad prediction of Mercury’s orbit Bad theory? Newton’s group of hypotheses
  43. 43. PHIL 160 Duhem says scientists must rely on “good sense” No set rule for how to fix group of hypotheses that makes a bad prediction.
  44. 44. PHIL 160 Holism in testing important in observations made with scientific instruments. Group includes hypotheses about the measuring device.
  45. 45. PHIL 160
  46. 46. PHIL 160 Theory predicts: room temp chicken is a good host for salmonella. Test prediction with microscope.
  47. 47. PHIL 160
  48. 48. PHIL 160 In the group of hypotheses: Theory about salmonella growth. Theory of the microscope. Bad prediction could mean a problem with either theory (or both)
  49. 49. PHIL 160 Quine : Hypotheses are tested in groups and the group includes all human knowledge claims (including meanings of terms). “ Meaning holism” Can’t test hypotheses in isolation, and changes in one hypothesis can prompt changes throughout whole logical structure of the theory.
  50. 50. PHIL 160 What does this have to do with the Twin Earth thought experiment?
  51. 51. PHIL 160
  52. 52. PHIL 160
  53. 53. PHIL 160 Is the stuff from Twin Earth water? Devise observations that could help you distinguish water from not-water.
  54. 54. PHIL 160
  55. 55. PHIL 160 Is the stuff from Twin Earth water? For every test, performs identically to water. Thus, reasonable to conclude (1600) it is water.
  56. 56. PHIL 160
  57. 57. PHIL 160 Is the stuff from Twin Earth water? New test: elemental analysis Water from Earth: H 2 O Stuff from Twin Earth: XYZ But is Twin Earth stuff water?
  58. 58. PHIL 160 Is the stuff from Twin Earth water? Because of meaning holism, this depends on the choices you make in evaluating the group of hypotheses.
  59. 59. PHIL 160 1. Water is the stuff found in rivers, lakes, streams, and aqueducts that humans drink, cook with, bathe in, swim in, etc.
  60. 60. PHIL 160 <ul><li>2. Water displays certain regular behaviors (boiling under certain specified conditions, freezing under certain specified conditions, dissolving particular amounts of certain substances, etc.). </li></ul>
  61. 61. PHIL 160 3. Although water from the ocean, water from a stream, water from a well, rainwater, etc., may differ in their impurities (salt, mud, etc.), they all count as water; that is, the substance containing these different impurities is the same.
  62. 62. PHIL 160 4. Water’s behavior is a result of what it is made of.
  63. 63. PHIL 160 5. If two samples display different microstructure (e.g., different elemental composition), they must be samples of different substances.
  64. 64. PHIL 160 6. Substances with different microstructures will display different macroscopic behavior.
  65. 65. PHIL 160 2 1 3 4 5 6 Group of hypotheses
  66. 66. PHIL 160 2 1 3 4 Drop these 2 1 3 5 6 4 Group of hypotheses
  67. 67. PHIL 160 Add “Water is H 2 O” 1 4 5 6 3 2 Drop these Group of hypotheses
  68. 68. PHIL 160 changing hypotheses can change meanings
  69. 69. Baptism: &quot;That stuff is water&quot; PHIL 160 Courtesy of the Frances Loeb Library, Graduate School of Design, Harvard University
  70. 70. Description: &quot;Water has the following properties ...&quot; PHIL 160 Freezing point Taste, color ... Boiling point Microscopic structure
  71. 71. PHIL 160 Courtesy of the Frances Loeb Library, Graduate School of Design, Harvard University &quot;That stuff (water) has these properties&quot;
  72. 72. Quine: PHIL 160 “ Any statement can be held to be true come what may, if we make drastic enough adjustments elsewhere in the system.”

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