david hume, the problem of induction - david barnett...david hume, the problem of induction an essay...
TRANSCRIPT
+
David Hume, The Problem of Induction An Essay Concerning Human Understanding, Sections II, III, IV, and V, Part I
+David Hume (1711 - 1776)
n from Scotland
n goal: science of the human mind
n notorious religious skeptic
n gained appreciation pothsumously
+A Treatise of Human Nature
n published anonymously
n “fell deadborn from the press, failing to elicit even a murmur from the zealots”
n Later popularizations: n An Enquiry Concerning
Human Understanding n An Enquiry Concerning
the Principles of Morals
+
Copy thesis Locke: All ideas come from experience.
Hume: All ideas are copies of impressions.
Argument: I can’t think of a counterexample.
Ideas vs. impressions: In Locke, “idea” is generic term
In Hume “perception” is generic, “ideas” and “impressions” different types of perceptions
Impressions have greater “force and vivacity”
+ The missing shade of blue Why is this a problem? What is Hume’s response?
+
Associationism Simple and universal principles of association:
1. Resemblance
2. Contiguity
3. Cause and effect
+Hume’s Enquiry, Matters of Fact and causal relations Section IV, Part I
+Cause and effect relations
n Questions about causation: n Metaphysical: What is it for one event to cause another?
n Psychological: How do we form the idea of causation? How do we arrive at causal judgments?
n Epistemological: When are we justified in making causal judgments?
n Hume’s psychological questions: 1. How do we apply the idea of causation to particular cases?
2. Where does the idea of causation come from?
n aka, From what impressions is the idea copied?
+Two “objects of human reason”
n Relations of Ideas: n Their contraries are
contradictions. n “Relations of Ideas” suggests
mere tautologies n All a priori truths, including all
mathematical truths
n Matters of Fact: n Their contraries are internally
consistent. n “Matters of Fact” suggests
substantive truths n Matters of Fact are known by
experience
+
Causal relations not Relations of Ideas Hume: ideas of causes separate from ideas of effects
Objection: macro causal relations explained by micro causal relations (“secret structure of parts”)
+ Conservation of Momentum not a Relation of Ideas • Hume: Laws of nature are Matters of Fact • no “secret structure of parts”
+ Could a baby genius figure it out? Baby genius can know all a priori mathematics and logic
Baby genius has idea of the particular events, has never seen them together.
+
Causal relations not a priori “Causes and effects are discoverable not by reason, but by experience.”
+How do we learn of causal relations through experience?
n Proposal 1: We experience them directly. n Baby genius could not know that bread causes nourishment after
one trial.
n Baby genius could not know conservation of momentum law after one trial.
n Proposal 2: We infer causal relations from repeated experience. n Baby genius would be convinced that bread causes nourishment
after many trials.
n Baby genius would be convinced of conservation of momentum law after many trials.
+Hume’s Enquiry, Skeptical doubts about induction Section IV, Part II
+“Necessary connexion” and “constant conjunction”
n If A causes B, then there is a necessary connection between A and B. n necessary connection: every time A happens, B must happen
n If there is a necessary connection, then there is a constant conjunction. n constant conjunction: every time A happens, B does happen
+Valid and invalid inferences
n Valid inference with true premises:
1. Every bachelor is a man.
2. Hume is a bachelor.
3. Therefore, Hume is a man.
n Valid inference with a questionable premise:
1. Every philosopher is wise.
2. Hume is a philosopher.
3. Therefore, Hume is a wise.
n Subtly invalid inference:
1. Every bachelor is a man.
2. Hume is a man.
3. Therefore, Hume is a bachelor.
n Obviously invalid inference:
1. Hume is a man.
2. Hume is a bachelor.
3. Therefore, every man is a bachelor.
Valid inferences Invalid inferences
+Adding premises to our obviously invalid inference
1. Hume is a man.
2. Hume is a bachelor.
3. Therefore, every man is a bachelor.
+Adding premises to our obviously invalid inference
1. Hume is a man.
2. Hume is a bachelor.
3. Descartes is a man.
4. Descartes is a bachelor.
5. Therefore, every man is a bachelor.
+Adding premises to our obviously invalid inference
1. Hume is a man.
2. Hume is a bachelor.
3. Descartes is a man.
4. Descartes is a bachelor.
5. Leibniz is a man.
6. Leibniz is a bachelor.
7. Therefore, every man is a bachelor.
+Adding premises to our obviously invalid inference 1. Hume is a man.
2. Hume is a bachelor.
3. Descartes is a man.
4. Descartes is a bachelor.
5. Leibniz is a man.
6. Leibniz is a bachelor.
7. Locke is a man.
8. Locke is a bachelor.
9. Therefore, every man is a bachelor.
+Adding premises to our obviously invalid inference 1. Hume is a man.
2. Hume is a bachelor.
3. Descartes is a man.
4. Descartes is a bachelor.
5. Leibniz is a man.
6. Leibniz is a bachelor.
7. Locke is a man.
8. Locke is a bachelor.
9. Kant is a man.
10. Kant is a bachelor.
11. Therefore, every man is a bachelor.
+Adding premises to our obviously invalid inference 1. Hume is a man.
2. Hume is a bachelor.
3. Descartes is a man.
4. Descartes is a bachelor.
5. Leibniz is a man.
6. Leibniz is a bachelor.
7. Locke is a man.
8. Locke is a bachelor.
9. Kant is a man.
10. Kant is a bachelor.
11. Arnauld is a man.
12. Arnauld is a bachelor.
13. Therefore, every man is a bachelor.
+Adding premises to our obviously invalid inference 1. Hume is a man.
2. Hume is a bachelor.
3. Descartes is a man.
4. Descartes is a bachelor.
5. Leibniz is a man.
6. Leibniz is a bachelor.
7. Locke is a man.
8. Locke is a bachelor.
9. Kant is a man.
10. Kant is a bachelor.
11. Arnauld is a man.
12. Arnauld is a bachelor.
13. Newton is a man.
14. Newton is a bachelor.
15. Therefore, every man is a bachelor.
+Adding premises to our obviously invalid inference 1. Hume is a man.
2. Hume is a bachelor.
3. Descartes is a man.
4. Descartes is a bachelor.
5. Leibniz is a man.
6. Leibniz is a bachelor.
7. Locke is a man.
8. Locke is a bachelor.
9. Kant is a man.
10. Kant is a bachelor.
11. Arnauld is a man.
12. Arnauld is a bachelor.
13. Newton is a man.
14. Newton is a bachelor.
15. Boyle is a man.
16. Boyle is a bachelor.
17. Therefore, every man is a bachelor.
+Adding premises to our obviously invalid inference 1. Hume is a man.
2. Hume is a bachelor.
3. Descartes is a man.
4. Descartes is a bachelor.
5. Leibniz is a man.
6. Leibniz is a bachelor.
7. Locke is a man.
8. Locke is a bachelor.
9. Kant is a man.
10. Kant is a bachelor.
11. Arnauld is a man.
12. Arnauld is a bachelor.
13. Newton is a man.
14. Newton is a bachelor.
15. Boyle is a man.
16. Boyle is a bachelor.
17. Spinoza is a man.
18. Spinoza is a bachelor.
19. Therefore, every man is a bachelor.
+
George Berkeley (1685 – 1753) 1. Berkeley is a man.
2. Berkeley is not a bachelor.
3. Therefore, not every man is a bachelor.
+The problem of induction
n In a deductively valid inference, the conclusion follows directly from the premises.
n But inductive inferences are “ampliative”—the conclusion goes beyond the premises.
n Classic examples of induction: n People have seen lots and lots of ravens, and every one has been
black. Therefore, all ravens are black.
n The sun has risen every morning in the past. Therefore, it will continue to rise in the future.
n How can you be justified in believing the conclusion of this invalid inference?
+Justifying induction
1. Induction worked today.
2. Induction worked yesterday.
3. Induction worked the day before yesterday.
4. etc., etc.
5. Therefore, induction will work tomorrow. ✕ Hume: This is an inductive inference, so it depends on prior justification
for induction.
First proposal: Induction has worked in the past.
+Justifying induction
1. Eating bread was followed by nourishment today.
2. Eating bread was followed by nourishment yesterday.
3. Eating bread was followed by nourishment the day before yesterday.
4. etc., etc.
5. Therefore, eating bread causes nourishment.
✕ Hume: This just makes the problem worse. (Necessary connection requires constant conjunction.)
6. Therefore, eating bread will be followed by nourishment tomorrow.
Second proposal: Inductive inferences supported by causal relations.
+Hume’s Enquiry, The “Sceptical Solution” Section V, Part I
+
Hume: causal judgments founded on custom or habit
“custom”: what you are accustomed to
Grandpa’s toast habit
+Responses to skepticism
Refutation of skepticism “Skeptical Solution”