David Hume 1711-1776

1. David Hume1711-1776

4. Ideas and Thinking Low force and vivacity Conception, volition, memory, imagination, etc. Impressions Feeling High force and vivacity Perception, emotion, pain, etc.

5. Nihil est in intellectu quod non antea fuerit in sensu Nothing is in the intellect that was not first in the senses The mind at birth is a blank slate, a tabula rasa Hume’s statement of empiricism: • All simple ideas are copies of impressions • Complex ideas may be copied from or constructed out of impressions

6. Arguments for empiricism • Counterfactual dependence • Those who don’t undergo the relevant experiences don’t acquire the relevant concepts • Analyzability • All legitimate complex concepts can be analyzed into simple concepts

7. Against Descartes • We can be mistaken about what we’re thinking • though it’s easier to be mistaken about ideas than impressions, since they’re less vivacious • Descartes is wrong to think there are pure ideas of the understanding. All ideas are ideas of the imagination • It follows that we cannot think about something we couldn’t experience!

8. Relations of Ideas knowledge obtained by mere investigation of our concepts A priori Necessary Denial is contradictory Matters of fact knowledge obtained by empirical investigation A posteriori Contingent Denial is consistent Two subjects of inquiry

9. Knowledge of matters of fact Direct knowledge: • Perception • Memory Indirect knowledge: • All involves knowledge of cause and effect • Too much alcohol causes hangovers • My car is in my driveway • More than half of Arkansas voters intend to vote for McCain • We will all eventually die

10. Perception Knowledge of matters of fact Direct knowledge Indirect knowledge • All involves knowledge of cause and effect • Too much alcohol causes hangovers • My car is in my driveway • More than half of Arkansas voters intend to vote for candidate x • There are 726 pages in this book • We will all eventually die Memory

11. How do we know cause and effect? All indirect a posteriori knowledge relies on it; where does it come from?

12. Not from reason • Causal connection not logically necessary • Unfamiliar causal relations not known by ideas alone • water suffocates • two sheets of marble can’t be pulled apart • Nothing inconceivable about billiard ball simply stopping after contact • Can’t deduce the effects from ultimate cause, because we don’t know ultimate cause

13. Belief in causation comes from experience But how? We only experience correlations: A is constantly conjoined with B We never experience a causal connection between them

14. The Problem of Induction Any argument whose conclusion goes beyond direct experience would have the following form: • A has always been followed by B. • Things we have not observed will resemble things we have • Therefore, the next A will be followed by B.

15. The Problem of Induction Any argument whose conclusion goes beyond direct experience would have the following form: • A has always been followed by B. • Things we have not observed will resemble things we have • Therefore, the next A will be followed by B. • All causal/experimental reasoning---all indirect knowledge of matters of fact---relies on the Uniformity Principle (UP): • Things we have not observed will resemble things we have

16. But how can we know the Uniformity Principle? Relation of Ideas (a priori) Matter of Fact(a posteriori) • UP can’t be a priori • contingent • denial is logically consistent Direct Indirect • UP can’t be direct • about things we haven’t experienced • UP can’t be indirect • all indirect matters of fact rely on UP • so argument would be circular

17. So we can’t have any reason to believe the Uniformity Principle • But all induction is based on the UP • So there’s no rational justification for inductive reasoning!

18. How/why do we form inductive beliefs? Habit/custom/conditioning • Repeated exposure to A being followed by B makes us expect B upon presentation of the next A • Not by any reasoning on our part • By a Pavlovian tendency of the mind to treat similar things as the same

19. Concept of causation • We never experience causal relations ---only constant conjunction --- in sensation or reflection • We can’t have an idea of something we can’t experience • Idea of causation comes from experience of our conditioned expectation • Not from experience of causation among external objects • So the concept of cause is subjective; it’s about us, not the world around us

20. Hume on Causation As cause Bs if and only if: Bs always follow As, and Upon observing an A, the mind anticipates occurrence of a B

21. Bertrand Russell(1872--1970)

22. Russell on the Problem of the External World We can’t prove the existence of mind-independent objects But, • We instinctively believe in them, and instinctive beliefs should be trusted unless there is a positive reason not to • The hypothesis that there is an enduring mind-independent world is simpler than any known hypothesis that would explain our experiences Ockham’s Razor: choose the simplest explanation, i.e., the one that posits fewer kinds of new entities