Hume’s Problem of Induction

1. Hume’s Problem of Induction

2. Hume’s Problem of Induction Most of our beliefs about the world have been formed from inductive inference. (e.g., all of science, folk physics/psych) Hume concludes that we have no reason at all to think these beliefs are true.

3. Hume’s Problem of Induction Epistemology: the study of knowledge and the justification of belief. A central sub-field in philosophy The problem of induction is a classic epistemological issue.

4. Plato (~2,500 years ago): Knowledge = justified true belief To have knowledge: A person must believe a proposition. She must believe it for good reasons. The proposition must be true.

5. Plato (~2,500 years ago): Knowledge = justified true belief To have knowledge: A person must believe a proposition. She must believe it for good reasons. The proposition must be true. Even if a belief is true, someone may hold it for the wrong reasons. Accidentally true beliefs aren’t knowledge.

6. Imagine seeing this in a tabloid: Brad and Angelina Adopt Three-headed Baby! Would you be justified in believing this just on the basis of a tabloid headline?

7. Imagine seeing this in a tabloid: Brad and Angelina Adopt Three-headed Baby! Even if it’s true, as long as your only reason for believing this is that you saw it in a tabloid, you don’t really know that Brad and Angelina have a three-headed baby. Your belief is based on bad reasons. You may have true belief but still lack justification.

8. This is the sort of objection Hume makes against induction:

9. This is the sort of objection Hume makes against induction: Inductive beliefs aren’t justified. They could be true, but we have no reason to think so. If they happen to be true, it’s just an accident.

10. The point is not that inductive beliefs are false, but that we can’t tell whether they’re false or not. • If they happen to be false, we won’t know it. • If they happen to be true, it’s just an accident.

11. According to Hume, We might as well get our scientific beliefs out of the tabloids.

12. Recall the difference: • Hume’s point is that the argumentssupporting • induction all fail. • He considers 3: • -2 deductive • -1 inductive Evaluating an argument Evaluating a conclusion

13. A severe form of skepticism Others have been skeptical of knowledge, rather than justification:

14. A severe form of skepticism Others have been skeptical of knowledge, rather than justification: • Descartes notes that knowledge requires certainty... • If you aren’t really sure about something, you can’t say you know. You just believe.

15. A severe form of skepticism Others have been skeptical of knowledge, rather than justification: • Descartes notes that knowledge requires certainty... • If you aren’t really sure about something, you can’t say you know. You just believe. ...then he shows that we aren’t certain about much. So we don’t know much.

16. A severe form of skepticism • Still, even if you don’t really know something, you can be justified in believing it. • Beliefs can at least be rational, even if you aren’t certain about them.

17. A severe form of skepticism • Still, even if you don’t really know something, you can be justified in believing it. • Beliefs can at least be rational, even if you aren’t certain about them. • Hume says you can’t even say this much in favor of induction: • It’s irrational to believe things for no good reason.

18. Hume’s Basic Argument: (PUN = Principle of Uniformity of Nature) Induction is justified only if PUN is justified. PUN can be justified only by induction or by deduction. PUN can’t be justified by induction. PUN can’t be justified by deduction. PUN can’t be justified at all. Induction isn’t justified.

19. What’s PUN? Uniformity between past and future Predictions of the future are based on patterns observed in the past. They assume that the patterns we’ve observed in the past will continue into the future.

20. What’s PUN? Patterns: A reliably comes before B. A B Fire Smoke Lightning Thunder Sunshine Sunburn

21. What’s PUN? In the past, lightning has reliably preceded thunder. 2) PUN: patterns from the past will continue in the future. In the future, lightning will continue to precede thunder.

22. What’s PUN? In the past, sunburns have reliably appeared after sun exposure. 2) PUN: patterns from the past will continue in the future. In the future, sunburns will continue to appear after sun exposure.

23. What’s PUN? Past = Future A B A B Fire Smoke Fire Smoke Sun Burn Sun Burn

24. Hume’s Basic Argument: Induction is justified only if PUN is justified. PUN can be justified only by induction or by deduction. PUN can’t be justified by induction. PUN can’t be justified by deduction. PUN can’t be justified at all. Induction isn’t justified.

25. Hume’s Basic Argument: Induction is justified only if PUN is justified.

26. Hume’s Basic Argument: Induction is justified only if PUN is justified. Consider this inference: In the past, lightning has reliably come before thunder. How do we make this connection? In the future, lightning will come before thunder.

27. Hume’s Basic Argument: Induction is justified only if PUN is justified. In the past, lightning has reliably come before thunder. Does this follow logically? In the future, lightning will come before thunder.

28. Hume’s Basic Argument: Induction is justified only if PUN is justified. In the past, lightning has reliably come before thunder. Does this follow logically? No. In the future, lightning will come before thunder.

29. Hume’s Basic Argument: Induction is justified only if PUN is justified. In the past, lightning has reliably come before thunder. 2) PUN: patterns from the past will continue in the future. In the future, lightning will come before thunder.

30. Hume’s Basic Argument: Induction is justified only if PUN is justified. Observation In the past, the sun has risen every morning. 2) PUN: patterns from the past will continue in the future. In the future, the sun will rise every morning. Prediction Without PUN, there’s no connection between observation and prediction.

31. Hume’s Basic Argument: Induction is justified only if PUN is justified. PUN can be justified only by induction or by deduction. PUN can’t be justified by induction. PUN can’t be justified by deduction. PUN can’t be justified at all. Induction isn’t justified.

32. Hume’s Basic Argument: Induction is justified only if PUN is justified. PUN can be justified only by induction or by deduction. Hume wrote before abduction was “discovered,” so induction and deduction were all he knew about. But would it matter? Could PUN be needed as the best explanation for something?

33. Discuss in groups: • Can PUN be justified by abduction? • Can you think of any observations that we might need PUN to explain? ??? OBS: PUN: patterns from the past will continue in the future. HYP:

34. PUN is a claim about what’s going to happen in the future. But to justify PUN by abduction we’d need to show that it’s the best explanation for something we’ve already observed. How could events that haven’t happened yet be the explanation for events that have already happened? Past ??? OBS: PUN: patterns from the past will continue in the future. HYP:

35. Hume’s Basic Argument: Induction is justified only if PUN is justified. PUN can be justified only by induction or by deduction. PUN can’t be justified by induction. PUN can’t be justified by deduction. PUN can’t be justified at all. Induction isn’t justified.

36. 3) PUN can’t be justified by induction. A natural thought is that the success of induction supports the truth of PUN: We constantly make predictions based on observed patterns, and most of them turn out to be accurate. The best explanation for this success is that patterns do continue into the future.

37. 3) PUN can’t be justified by induction. But look closely: have made turned out We constantly make predictions based on observed patterns, and most of them turn out to be accurate. The best explanation for this success is that patterns do continue into the future. did Observed cases of successful prediction have all occurred in the past.

38. 3) PUN can’t be justified by induction. But look closely: have made turned out We constantly make predictions based on observed patterns, and most of them turn out to be accurate. The best explanation for this success is that patterns do continue into the future. did This showsonly that nature was uniform, back when the predictions were tested.

39. In the past, the sun has risen every morning. In the future, the sun will rise every morning. In the past, patterns from the past continued into the future. In the future, patterns from the past will continue into the future.

40. In the past, the sun has risen every morning. 2) PUN: patterns from the past will continue in the future. In the future, the sun will rise every morning. In the past, patterns from the past continued into the future. In the future, patterns from the past will continue into the future.

41. In the past, the sun has risen every morning. 2) PUN: patterns from the past will continue in the future. In the future, the sun will rise every morning. In the past, patterns from the past continued into the future. 2) PUN: patterns from the past will continue in the future. In the future, patterns from the past will continue into the future.

42. In the past, the sun has risen every morning. 2) PUN: patterns from the past will continue in the future. In the future, the sun will rise every morning. In the past, patterns from the past continued into the future. 2) PUN: patterns from the past will continue in the future. In the future, patterns from the past will continue into the future.

43. The argument is circular. Induction only works if PUN is already true (Premise 1), so any attempt to justify PUN using an inductive argument will have to assume its own conclusion in the premises. In the past, patterns from the past continued into the future. 2) PUN: patterns from the past will continue in the future. In the future, patterns from the past will continue into the future.

44. Hume’s Basic Argument: Induction is justified only if PUN is justified. PUN can be justified only by induction or by deduction. PUN can’t be justified by induction. PUN can’t be justified by deduction. PUN can’t be justified at all. Induction isn’t justified.

45. 4) PUN can’t be justified by deduction.

46. 4) PUN can’t be justified by deduction. Hume considers two ways that PUN might be justified by deduction: If we could deduce the uniformity of nature directly from what we observe. If it followed somehow from the meaning of PUN that nature was uniform. Neither approachworks.

47. 4) PUN can’t be justified by deduction. Could we deduce uniformity directly from what we observe? This would mean that facts about the future follow logically from what we’ve observed the past.

48. 4) PUN can’t be justified by deduction. Could we deduce uniformity directly from what we observe? This would mean that facts about the future follow logically from what we’ve observed the past. But we’ve already considered this...

49. 4) PUN can’t be justified by deduction. Could we deduce uniformity directly from what we observe? In the past, the sun has risen every morning. Does this follow logically? In the future, the sun will rise every morning.

50. 4) PUN can’t be justified by deduction. Could we deduce uniformity directly from what we observe? In the past, the sun has risen every morning. No. Does this follow logically? In the future, the sun will rise every morning.