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How We Think: Rethinking Beliefs and Reasoning in Philosophy and Psychology

Explore the works of Richard Pettigrew, Epicurus, René Descartes, Elizabeth Harman, Daniel Kahneman, Amos Tversky, Patricia Wason, and Marilyn vos Savant to understand how our thinking processes shape our beliefs and reasoning.

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How We Think: Rethinking Beliefs and Reasoning in Philosophy and Psychology

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  1. How we think (and how we ought to) Richard Pettigrew Department of Philosophy University of Bristol richardpettigrew.wordpress.com

  2. Epicurus341BC – 270BC

  3. Epicurus341BC – 270BC Accustom yourself to believe that death is nothing to us, for good and evil imply awareness, and death is the privation of all awareness […] Death, therefore, the most awful of evils, is nothing to us, seeing that, when we are, death is not come, and, when death is come, we are not. It is nothing, then, either to the living or to the dead, for with the living it is not and the dead exist no longer. Letter to Menoeceus, trans. Robert Drew Hicks

  4. René Descartes1596 – 1650

  5. René Descartes1596 – 1650 Some years ago I was struck by how many false things I had believed, and by how doubtful was the structure of beliefs that I had based on them. I realized that if I wanted to establish anything in the sciences that was stable and likely to last, I needed—just once in my life—to demolish everything completely and start again from the foundations. […] I am here quite alone, and at last I will devote myself, sincerely and without holding back, to demolishing my opinions. Descartes, Meditations on First Philosophy, trans. Bennett

  6. Elizabeth Harman

  7. Elizabeth Harman • If I go to the gym, I’ll be glad I did it. • Therefore, I’ll go to the gym. • If I become an arms trader, I’ll be glad I did it. • Therefore, I’ll become an arms trader.

  8. Daniel Kahneman Amos Tversky

  9. When she was a student, Jane was a member of the CND and the Green Party and the Migrants Rights Centre in Bristol. • Jane is an accountant and a political activist • Jane is an accountant

  10. Conjunction Fallacy • When she was a student, Jane was a member of the CND and the Green Party and the Migrants Rights Centre in Bristol. • Jane is an accountant and a political activist • Jane is an accountant Tversky, A. and Kahneman, D. (1983) ‘Extension versus intuitive reasoning: The conjunction fallacy in probability judgment’ Psychological Review 90(4):293-315

  11. WasonFour-Card Task CLAIM: If there is an even number on one side, there is a vowel on the other. K 3 8 O Wason, P. C. (1968) ‘Reasoning about a rule’ Quarterly Journal of Experimental Psychology, 20(3):273-281

  12. WasonFour-Card Task CLAIM: If there is an even number on one side, there is a vowel on the other. K 3 8 O Wason, P. C. (1968) ‘Reasoning about a rule’ Quarterly Journal of Experimental Psychology, 20(3):273-281

  13. WasonFour-Card Task CLAIM: If there is an even number on one side, there is a vowel on the other. K 3 8 O Wason, P. C. (1968) ‘Reasoning about a rule’ Quarterly Journal of Experimental Psychology, 20(3):273-281

  14. WasonFour-Card Task CLAIM: If someone is drinking alcohol, then they are over eighteen. Wason, P. C. (1968) ‘Reasoning about a rule’ Quarterly Journal of Experimental Psychology, 20(3):273-281

  15. WasonFour-Card Task CLAIM: If someone is drinking alcohol, then they are over eighteen. Wason, P. C. (1968) ‘Reasoning about a rule’ Quarterly Journal of Experimental Psychology, 20(3):273-281

  16. Harvard Medical School test A test is developed. A mystery disease is discovered. Incidence: 1 in 10,000 • We give Jane the test and she tests positive. • How confident should we be that she has the illness? (a) 1% (b) 50% (c) 95%

  17. Harvard Medical School test Ill 6,000 Not ill 60,000,000 – 6,000

  18. Harvard Medical School test Ill 6,000 Not ill 59,994,000

  19. Test positive Test negative Ill 99% of 6,000 1% of 6,000 Not ill 59,994,000

  20. Test positive Test negative Ill 5,940 60 Not ill 59,994,000

  21. Test positive Test negative Ill 5,940 60 99% of 59,994,000 1% of 59,994,000 Not ill

  22. Test positive Test negative Ill 5,940 60 599,940 59,394,060 Not ill

  23. Test positive 5,940 5,940 + 599,940 Ill 5,940 = 5,940 605,880 599,940 Not ill < 0.01

  24. We give Jane the test and she tests positive. • How confident should we be that she has the illness? (a) 1% (b) 50% (c) 95% Casscells, W., SchoenbergerA., and Graboys, T. B. (1978) ‘Interpretation by physicians of clinical laboratory results’ New England Journal of Medicine,299(18):999-1001

  25. Monty Hall Puzzle Marilyn vos Savant World’s highest IQ Author of ‘Ask Marilyn’

  26. Monty Hall Puzzle 3 1 2

  27. Monty Hall Puzzle 3 1 2

  28. Monty Hall Puzzle 3 1 2

  29. Monty Hall Puzzle 3 1 2

  30. Monty Hall Puzzle Pick a door! I will then open a different door to reveal a goat. 3 1 2

  31. Monty Hall Puzzle 3 1 2

  32. Monty Hall Puzzle 3 1 2

  33. Monty Hall Puzzle You can now stick or switch. Whichever door you pick, you’ll win whatever’s behind it. 3 1 2

  34. Monty Hall Puzzle Switch! There’s a 2/3 chance the car’s behind door 3. 3 1 2

  35. Monty Hall Puzzle Doesn’t matter whether you switch. It’s ½ chance either way. 3 1 2

  36. Why vos Savant is right 1 2 3

  37. Why vos Savant is right 1 2 3 1/3 1/3 1/3

  38. Why vos Savant is right 1 2 3 1/3 Door 2 1/3 Door 3 0 Door 2 0 1/3 Door 3 1/3 Door 2 1/6 1/3 Door 3 1/6

  39. Why vos Savant is right 1 2 3 1/3 Door 2 1/3 Door 3 0 Door 2 0 1/3 Door 3 1/3 Door 2 1/6 1/3 Door 3 1/6

  40. Under-represented groupsamongst academic staff

  41. Conjunction Fallacy and Prototypes In the Conjunction Fallacy, we substitute the easier question How close is Jane to the prototypical exemplar of this group? in place of the more difficult question How likely is Jane to be a member of this group? Kahneman, D. and S. Frederick (2002) ‘Representativeness Revisited: Attribute Substitution in Intuitive Judgment’ In: Thomas Gilovich et al. (eds.) Heuristics and Biases, pp. 49-81 (Cambridge: CUP)

  42. Conjunction Fallacy and Prototypes Similarly, when in hiring, promotions, and other assessment situations, we substitute the easier question How close is the candidate to the prototypical exemplar of successful people in this endeavour? in place of the more difficult question How good is the candidate at this endeavour? Kahneman, D. and S. Frederick (2002) ‘Representativeness Revisited: Attribute Substitution in Intuitive Judgment’ In: Thomas Gilovich et al. (eds.) Heuristics and Biases, pp. 49-81 (Cambridge: CUP)

  43. Implicit bias • 238 academic psychologists (118 male, 120 female) evaluated a CV randomly assigned a male or a female name. • Both male and female participants were twice as likely to hire the male applicant. Steinpreis, R., Anders, K., and Ritzke, D. (1999) ‘The Impact of Gender on the Review of the Curricula Vitae of Job Applicants and Tenure Candidates: A National Empirical Study’ Sex Roles, 41(7/8):509-528

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