David Hume1711-1776

Ideas andThinking

Low force and vivacity

Conception, volition, memory, imagination, etc.

ImpressionsFeeling

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 The mind at birth is a blank slate, a tabula rasatabula rasa

Hume’s statement of empiricism:Hume’s statement of empiricism: All simple ideas are copies of impressionsAll simple ideas are copies of impressions

Complex ideas may be copied from or constructed out Complex ideas may be copied from or constructed out of impressionsof impressions

Arguments for empiricism

1.1. Counterfactual dependenceCounterfactual dependence Those who don’t undergo the relevant Those who don’t undergo the relevant

experiences don’t acquire the relevant experiences don’t acquire the relevant conceptsconcepts

2.2. Analyzability Analyzability All legitimate complex concepts can be All legitimate complex concepts can be

analyzed into simple conceptsanalyzed into simple concepts

Against Descartes

We can be mistaken about what we’re thinkingWe can be mistaken about what we’re thinking though it’s easier to be mistaken about ideas than though it’s easier to be mistaken about ideas than

impressions, since they’re less vivaciousimpressions, since they’re less vivacious

Descartes is wrong to think there are pure ideas Descartes is wrong to think there are pure ideas of the understanding. All ideas are ideas of the of the understanding. All ideas are ideas of the imaginationimagination

It follows that we cannot think about something It follows that we cannot think about something we couldn’t experience!we couldn’t experience!

Two subjects of inquiry

Relations of IdeasRelations of Ideasknowledge obtained knowledge obtained by mere investigation by mere investigation of our conceptsof our concepts

A prioriA priori NecessaryNecessary Denial is contradictoryDenial is contradictory

Matters of factMatters of factknowledge obtained knowledge obtained by empirical by empirical investigationinvestigation

A posterioriA posteriori ContingentContingent Denial is consistentDenial is consistent

Knowledge of matters of fact

Direct knowledge:Direct knowledge: PerceptionPerception MemoryMemory

Indirect knowledge:Indirect knowledge: All involves knowledge of cause and effectAll involves knowledge of cause and effect

Too much alcohol causes hangoversToo much alcohol causes hangovers My car is in my drivewayMy car is in my driveway More than half of Arkansas voters intend to vote for McCainMore than half of Arkansas voters intend to vote for McCain We will all eventually dieWe will all eventually die

Knowledge of matters of fact

Perception

Direct knowledge Indirect knowledgeAll 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 All indirect a posteriori a posteriori knowledge relies on knowledge relies on it; where does it come from?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?But how?

We only experience correlations: A is We only experience correlations: A is constantly conjoined with Bconstantly conjoined with B

We never experience a causal connection We never experience a causal connection between thembetween them

The Problem of Induction

Any argument whose conclusion goes beyond direct experience would have the following form:

1. A has always been followed by B.2. Things we have not observed will resemble things we

have3. 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:

1. A has always been followed by B.2. Things we have not observed will resemble things we

have3. 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)

Direct Indirect

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 So we can’t have any any reason to believe reason to believe the Uniformity Principlethe Uniformity Principle

But all induction is based on the UPBut 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/conditioningHabit/custom/conditioning

Repeated exposure to A being followed by Repeated exposure to A being followed by B makes us expect B upon presentation of B makes us expect B upon presentation of the next Athe next ANot by any reasoning on our partNot by any reasoning on our partBy a Pavlovian tendency of the mind to treat By a Pavlovian tendency of the mind to treat

similar things as the samesimilar things as the same

Concept of causation We never experience causal relations ---only We never experience causal relations ---only

constant conjunction --- in sensation or reflectionconstant conjunction --- in sensation or reflection We can’t have an idea of something we can’t We can’t have an idea of something we can’t

experienceexperience Idea of causation comes from experience of our Idea of causation comes from experience of our

conditioned expectationconditioned expectation Not from experience of causation among external Not from experience of causation among external

objectsobjects

So the concept of cause is subjective; it’s about So the concept of cause is subjective; it’s about us, not the world around usus, not the world around us

Hume on Causation

As As cause Bs if and only if: Bs if and only if:

Bs always follow As, andBs always follow As, and

Upon observing an A, the mind anticipates Upon observing an A, the mind anticipates occurrence of a Boccurrence of a B

Bertrand Russell(1872--1970)

Russell on the Problem of the External World

We can’t prove the existence of mind-independent We can’t prove the existence of mind-independent objectsobjects

But, But, a.a. We instinctively believe in them, and instinctive We instinctively believe in them, and instinctive

beliefs should be trusted unless there is a beliefs should be trusted unless there is a positive reason not topositive reason not to

b.b. The hypothesis that there is an enduring mind-The hypothesis that there is an enduring mind-independent world is simpler than any known independent world is simpler than any known hypothesis that would explain our experienceshypothesis that would explain our experiences

Ockham’s Razor:Ockham’s Razor: choose the simplest explanation, choose the simplest explanation, i.e., the one that posits fewer kinds of new entitiesi.e., the one that posits fewer kinds of new entities