David Hume

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

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 All simple ideas are copies of impressions Complex ideas may be copied from or constructed out of impressions Complex ideas may be copied from or constructed out of impressions

Arguments for empiricism 1. Counterfactual dependence Those who don’t undergo the relevant experiences don’t acquire the relevant concepts Those who don’t undergo the relevant experiences don’t acquire the relevant concepts 2. Analyzability All legitimate complex concepts can be analyzed into simple concepts All legitimate complex concepts can be analyzed into simple concepts

Against Descartes We can be mistaken about what we’re thinking 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 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 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! It follows that we cannot think about something we couldn’t experience!

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

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

Knowledge of matters of fact Perception Direct knowledgeIndirect 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

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

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

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

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.

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

But how can we know the Uniformity Principle? Relation of Ideas (a priori) Matter of Fact (a posteriori) DirectIndirect UP can’t be a priori contingent denial is logically consistent 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

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

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 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 Not by any reasoning on our part By a Pavlovian tendency of the mind to treat similar things as the same By a Pavlovian tendency of the mind to treat similar things as the same

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

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

Bertrand Russell ( )

Russell on the Problem of the External World We can’t prove the existence of mind-independent objects But, a. We instinctively believe in them, and instinctive beliefs should be trusted unless there is a positive reason not to b. 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