David Hume:David Hume:Scepticism, Science,Scepticism, Science,

and Superstition and Superstition

Dr Peter MillicanDr Peter Millican

Hertford College, OxfordHertford College, Oxford

2. Newton to Berkeley2. Newton to Berkeleyand Humeand Hume

22

The Intelligibility of the WorldThe Intelligibility of the World

Aristotle’s world is intelligible because it is Aristotle’s world is intelligible because it is completely driven by completely driven by purposespurposes – even – even inanimate objects inanimate objects strivestrive towards goals. towards goals.

However Galileo, Descartes, Hobbes etc. However Galileo, Descartes, Hobbes etc. dismissed this as an illusion:dismissed this as an illusion:– Aristotle’s purposes just Aristotle’s purposes just describedescribe what objects what objects

actually do – they don’t actually do – they don’t explainexplain it at all. it at all.– Only mechanical interactions are genuinely Only mechanical interactions are genuinely

intelligibleintelligible, enabling us to understand , enabling us to understand whywhy things act as they do.things act as they do.

33

Why Intelligibility Matters (i)Why Intelligibility Matters (i)

Man is distinctively rational, made in the Man is distinctively rational, made in the image of God to understand His universe.image of God to understand His universe.– The rational nature of the universe proves the The rational nature of the universe proves the

existence of a supreme designing intelligence existence of a supreme designing intelligence (the (the Design ArgumentDesign Argument).).

– Our own ability to understand the universe Our own ability to understand the universe reveals our partially divine nature, quite reveals our partially divine nature, quite distinct from that of the brute animals.distinct from that of the brute animals.

– Geometric physics gets closest to the pure Geometric physics gets closest to the pure rational insight of divine Reason.rational insight of divine Reason.

44

Why Intelligibility Matters (ii)Why Intelligibility Matters (ii)

The intelligibility of matter reveals its The intelligibility of matter reveals its powerspowers, but equally importantly its , but equally importantly its limitslimits::– Matter is merely passive or Matter is merely passive or inertinert; minds are ; minds are

genuinely genuinely activeactive..– Thinking matter is impossible, so there must Thinking matter is impossible, so there must

be an immaterial substance, making the soul be an immaterial substance, making the soul potentially independent of the body.potentially independent of the body.

– Mental (“moral”) causation is fundamentally Mental (“moral”) causation is fundamentally different from physical causation, and this is different from physical causation, and this is the basis of free will.the basis of free will.

55

Meanwhile,Meanwhile,in the Heavens …in the Heavens …

In 1627 Johannes Kepler published tables In 1627 Johannes Kepler published tables enabling the calculation of planetary positions enabling the calculation of planetary positions to an accuracy which turned out to be over to an accuracy which turned out to be over 1000 times better than any previous method.1000 times better than any previous method.

Kepler’s method is based on the hypothesis Kepler’s method is based on the hypothesis that each planet moves in an that each planet moves in an ellipseellipse around around the Sun (which is at one “focus” of the ellipse).the Sun (which is at one “focus” of the ellipse).

The method’s sheer accuracy led over time to The method’s sheer accuracy led over time to general acceptance of that hypothesis.general acceptance of that hypothesis.

66

Newtonian PhysicsNewtonian Physics

Isaac Newton took Isaac Newton took Descartes’ concept of Descartes’ concept of inertia, and Boyle’s theory inertia, and Boyle’s theory of “atoms and the void”, but of “atoms and the void”, but

postulated a force of gravity acting through it.postulated a force of gravity acting through it.– If gravity acts in inverse proportion to the square If gravity acts in inverse proportion to the square

of the distance between two objects, and bodies of the distance between two objects, and bodies accelerate in proportion to the total force acting accelerate in proportion to the total force acting on them, then the elliptical motion of the planets on them, then the elliptical motion of the planets around the Sun can be elegantly explained.around the Sun can be elegantly explained.

77

Refuting Aristotle and DescartesRefuting Aristotle and Descartes

Newton’s theory could also predict – using Newton’s theory could also predict – using the very same equations – the motion of the very same equations – the motion of cannonballs etc. on Earth.cannonballs etc. on Earth.– Another nail in the coffin of the Aristotelian Another nail in the coffin of the Aristotelian

supposition that heavenly bodies act differently.supposition that heavenly bodies act differently.

In his In his Philosophiae Naturalis Principia Philosophiae Naturalis Principia MathematicaMathematica (1687), Newton also proved (1687), Newton also proved mathematical results indicating that a vortex mathematical results indicating that a vortex could not possibly generate elliptical motion.could not possibly generate elliptical motion.– Descartes’ theory was thereby discredited.Descartes’ theory was thereby discredited.

88

Gravitation and IntelligibilityGravitation and Intelligibility

Newtonian gravity acts at a distance with Newtonian gravity acts at a distance with no intermediate mechanical connexionno intermediate mechanical connexion..– But this is deeply “unintelligible”.But this is deeply “unintelligible”.– Descartes had objected to the idea of gravity Descartes had objected to the idea of gravity

as “occult”: one body would have to “know” as “occult”: one body would have to “know” where the other was to move towards it.where the other was to move towards it.

– Many Newtonians took the operation of Many Newtonians took the operation of gravity to be proof of divine action, a new gravity to be proof of divine action, a new resource against Hobbist materialism.resource against Hobbist materialism.

– Newton took a more Newton took a more instrumentalistinstrumentalist attitude. attitude.

99

Newton’s Methodological Newton’s Methodological InstrumentalismInstrumentalism

Newton’s public response to the objection:Newton’s public response to the objection:““Hypotheses non fingo”Hypotheses non fingo”

– ““I feign no hypotheses”; there’s no obligation to I feign no hypotheses”; there’s no obligation to invent speculations about how gravity operates invent speculations about how gravity operates (at least until more evidence comes to light (at least until more evidence comes to light giving a basis for more than giving a basis for more than meremere hypothesis). hypothesis).

– If the gravitational equations (etc.) correctly If the gravitational equations (etc.) correctly describe the observed behaviour of objects, describe the observed behaviour of objects, then that theory should be accepted whatever then that theory should be accepted whatever the unperceived underlying reality might be.the unperceived underlying reality might be.

1010

The Dilemma of GravityThe Dilemma of Gravity

If gravity is a power intrinsic to matter:If gravity is a power intrinsic to matter:– Matter can have powers beyond those implied Matter can have powers beyond those implied

by its nature as extended and inert.by its nature as extended and inert.– The ideal of intelligibility is thereby violated.The ideal of intelligibility is thereby violated.– Gravity seems to be an “active” power, Gravity seems to be an “active” power,

generating new movement. But if matter can generating new movement. But if matter can have have thisthis active power, why not others (e.g. active power, why not others (e.g. thought)? What then of immortality??thought)? What then of immortality??

If gravity is not intrinsic to matter:If gravity is not intrinsic to matter:– What becomes of our scientific endeavours?What becomes of our scientific endeavours?

1111

What about Mechanical Causation?What about Mechanical Causation?

Malebranche and Hume went on to deny the Malebranche and Hume went on to deny the intelligibility even of mechanical causation:intelligibility even of mechanical causation:– Suppose we see a yellow billiard ball moving Suppose we see a yellow billiard ball moving

towards a red one and colliding with it. Why do towards a red one and colliding with it. Why do we expect the red one to move?we expect the red one to move?

1212

Hume’s Thought Experiment (Hume’s Thought Experiment (EE 4.6) 4.6)

Imagine Adam, newly created by God, Imagine Adam, newly created by God, trying to envisage what would happen:trying to envisage what would happen:

– how could he possibly how could he possibly make any prediction at all make any prediction at all in advance of experience?in advance of experience?

1313

““Intelligibility” and ExperienceIntelligibility” and Experience

The “intelligibility” of mechanical causation The “intelligibility” of mechanical causation seems to be an illusion, based on familiarity.seems to be an illusion, based on familiarity.

When we have repeated experience, our When we have repeated experience, our expectation comes so naturally that we expectation comes so naturally that we imagine we could have known – even the imagine we could have known – even the first time – what would happen.first time – what would happen.

That’s wrong: only experience can tell us That’s wrong: only experience can tell us what causes what. what causes what. A prioriA priori, we have no , we have no understanding even of mechanical impact!understanding even of mechanical impact!

1414

Malebranche and HumeMalebranche and Hume

MalebrancheMalebranche– Insists that causes must beInsists that causes must be

intelligible, hence no naturalintelligible, hence no natural“causes” are really “causes” are really truetrue causes. causes.

– ““Occasionalism”: a step towardsOccasionalism”: a step towardsBerkeley’s “immaterialism”.Berkeley’s “immaterialism”.

HumeHume– Takes Newton’s methodological instrumentalism Takes Newton’s methodological instrumentalism

to its logical limit: intelligibility isn’t a requirement to its logical limit: intelligibility isn’t a requirement for any causes at allfor any causes at all..

– Constant conjunction is sufficent for a Constant conjunction is sufficent for a truetrue cause. cause.

1515

Malebranche and CausationMalebranche and Causation

Matter is inert, and has no causal impact Matter is inert, and has no causal impact on the world; the only cause is God.on the world; the only cause is God.– A real cause must A real cause must necessitatenecessitate its effect, but we its effect, but we

can conceive any physical “cause” occurring can conceive any physical “cause” occurring without its “effect”, so it can’t be a real cause.without its “effect”, so it can’t be a real cause.

– Only the will of an omnipotent Being can truly Only the will of an omnipotent Being can truly necessitate an effect in this sense.necessitate an effect in this sense.

– God sustains the world, in effect re-creating it God sustains the world, in effect re-creating it from moment to moment (as Descartes taught), from moment to moment (as Descartes taught), hence again He brings everything about.hence again He brings everything about.

1616

Malebranche’s OccasionalismMalebranche’s Occasionalism

Malebranche’s theory implies that physical Malebranche’s theory implies that physical objects are not real causes.objects are not real causes.– Instead they are “occasional” causes: when Instead they are “occasional” causes: when

one billiard ball hits another, this provides the one billiard ball hits another, this provides the occasionoccasion for God to cause the second to move for God to cause the second to move (by re-creating it in a sequence of positions).(by re-creating it in a sequence of positions).

– God also creates the visual ideas in our mind God also creates the visual ideas in our mind corresponding to this physical reality.corresponding to this physical reality.

– But then why not do away with the physical But then why not do away with the physical reality entirely, as it seems to play no role?reality entirely, as it seems to play no role?

1717

Berkeley’s ImmaterialismBerkeley’s Immaterialism

Berkeley’s immaterialism is essentially Berkeley’s immaterialism is essentially occasionalism without the material world. occasionalism without the material world. But he uses a different set of arguments:But he uses a different set of arguments:– Combines Lockean principle that only ideas are Combines Lockean principle that only ideas are

immediately perceived, with plain man’s belief immediately perceived, with plain man’s belief that trees etc. are immediately perceived;that trees etc. are immediately perceived;

– ““Veil of perception” scepticism is avoided by Veil of perception” scepticism is avoided by identifying objects with perceptions;identifying objects with perceptions;

– Attacks basis of primary/secondary quality Attacks basis of primary/secondary quality distinction, while insisting that ideas are inert.distinction, while insisting that ideas are inert.

1818

Locke’s Indirect RealismLocke’s Indirect Realism

Idea in the mindIdea in the mind(directly perceived)(directly perceived)

Material objectMaterial object(cause of the idea)(cause of the idea)

But if the tree But if the tree isis just what we directly perceive, just what we directly perceive, then there is no room for scepticism about it.then there is no room for scepticism about it.

1919

The Status of Secondary QualitiesThe Status of Secondary Qualities

Suppose a circular hotplate on an oven is Suppose a circular hotplate on an oven is glowing red hot. I bring my hand close to glowing red hot. I bring my hand close to it and feel warmth, then pain …it and feel warmth, then pain …

– The sensations of felt warmth and pain are The sensations of felt warmth and pain are clearly “in the mind”.clearly “in the mind”.

– The circular shape of the hotplate is, we are The circular shape of the hotplate is, we are inclined to say, “really in the object”.inclined to say, “really in the object”.

– So is the red colour of the hotplate “in the So is the red colour of the hotplate “in the mind” or “in the object”?mind” or “in the object”?

2020

A Problematic TextA Problematic Text

Locke’s Locke’s Essay,Essay, II viii 10: II viii 10:““Such Such QualitiesQualities, which in truth are nothing in , which in truth are nothing in the Objects themselves, but Powers to the Objects themselves, but Powers to produce various Sensations in us by their produce various Sensations in us by their primary Qualitiesprimary Qualities, , i.e.i.e. by the Bulk, Figure, by the Bulk, Figure, Texture, and Motion of their insensible parts, Texture, and Motion of their insensible parts, as Colours, Sounds, Tasts, as Colours, Sounds, Tasts, etc.etc. These I call These I call secondary Qualitiessecondary Qualities..

The comma before “but” is unfortunate. The comma before “but” is unfortunate. Locke means “nothing … but powers”.Locke means “nothing … but powers”.

2121

In Objects, or Just In the Mind?In Objects, or Just In the Mind?

Locke sees Locke sees bothboth PQs and SQs as genuine PQs and SQs as genuine properties of objects, but the SQs are nothing properties of objects, but the SQs are nothing but but powers due to their PQspowers due to their PQs..

Berkeley read Locke as saying that SQs are only Berkeley read Locke as saying that SQs are only “in the mind” and “in the mind” and notnot really properties of objects. really properties of objects.

But Locke is clear that our simple perceptions of But Locke is clear that our simple perceptions of objects’ colour etc. are “adequate”: they objects’ colour etc. are “adequate”: they faithfullyfaithfully represent their “archetypes” (II xxxi 1, 12):represent their “archetypes” (II xxxi 1, 12):

““SimpleSimple Ideas … are … certainly Ideas … are … certainly adequateadequate. Because . Because being intended to express nothing but the power in being intended to express nothing but the power in Things to produce in the Mind such a Sensation …”Things to produce in the Mind such a Sensation …”

2222

Why Resemblance?Why Resemblance?

Hence the emphasis on Hence the emphasis on resemblanceresemblance, , rather than rather than real existence in objectsreal existence in objects, as , as the key distinction between PQs and SQs:the key distinction between PQs and SQs:

““the the Ideas of primary QualitiesIdeas of primary Qualities of Bodies, of Bodies, are are Resemblances Resemblances of them, and their Patterns do of them, and their Patterns do really exist in the Bodies themselves; but the really exist in the Bodies themselves; but the Ideas, producedIdeas, produced in us in us byby these these Secondary Secondary Qualities, have no resemblanceQualities, have no resemblance of them at all. of them at all. There is nothing like our There is nothing like our IdeasIdeas, existing in the , existing in the Bodies themselves.” (II viii 15)Bodies themselves.” (II viii 15)

2323

Can an Idea Resemble an Object?Can an Idea Resemble an Object?

Berkeley (Berkeley (PrinciplesPrinciples I 8) is emphatic that: I 8) is emphatic that:““an idea can be like nothing but an idea; a an idea can be like nothing but an idea; a colour or figure can be like nothing but another colour or figure can be like nothing but another colour or figure.”colour or figure.”

His attack on Locke’s resemblance thesis His attack on Locke’s resemblance thesis seems to be based on the principle that seems to be based on the principle that ideas are ideas are intrinsically intrinsically “perceivable”.“perceivable”.

A further point concerns their A further point concerns their inertnessinertness – – nothing that is like our ideas of PQs could nothing that is like our ideas of PQs could be a real cause (be a real cause (PrinciplesPrinciples I 25). I 25).

2424

Another PQ/SQ ContrastAnother PQ/SQ Contrast

Ideas of SQs seem intrinsically perceivable – Ideas of SQs seem intrinsically perceivable – nothing can be like a nothing can be like a sensedsensed colour unless it colour unless it is is mental mental (as with a (as with a feltfelt pain). pain).

But ideas of PQs seem to lack this intimate But ideas of PQs seem to lack this intimate connexion with mentality – they are more connexion with mentality – they are more abstractabstract and and structuralstructural, as illustrated by their , as illustrated by their use in geometrical mechanics.use in geometrical mechanics.

So it’s plausible that ideas of PQs So it’s plausible that ideas of PQs cancan resemble non-mental reality in a resemble non-mental reality in a structuralstructural way (cf. Lowe on Locke, pp. 57, 63).way (cf. Lowe on Locke, pp. 57, 63).

2525

SoliditySolidity

However However soliditysolidity seems to be an odd man seems to be an odd man out – our idea of solidity seems clearly to be out – our idea of solidity seems clearly to be the idea of a the idea of a powerpower (or rather, perhaps, the (or rather, perhaps, the unknown unknown groundground of a power), and without of a power), and without any resemblance to a property of objects.any resemblance to a property of objects.

Solidity is a power to exclude other bodies. Solidity is a power to exclude other bodies. But what But what isis a body? a body?

Body is distinguished from empty space by Body is distinguished from empty space by its solidity, so the whole thing is circular!its solidity, so the whole thing is circular!

2626

Hume’s Criticism (Hume’s Criticism (TreatiseTreatise I iv 4) I iv 4)

““Two non-entities cannot exclude each other from Two non-entities cannot exclude each other from their places … Now I ask, what idea do we form of their places … Now I ask, what idea do we form of these bodies or objects, to which we suppose these bodies or objects, to which we suppose solidity to belong? To say, that we conceive them solidity to belong? To say, that we conceive them merely as solid, is to run on merely as solid, is to run on in infinitumin infinitum. … . … Extension must necessarily be consider’d either as Extension must necessarily be consider’d either as colour’d, which is a false idea [because it’s a SQ, colour’d, which is a false idea [because it’s a SQ, supposed not to be “in” objects]; or as solid, which supposed not to be “in” objects]; or as solid, which brings us back to the first question. … [Hence] after brings us back to the first question. … [Hence] after the exclusion of colours (etc.) from the rank of the exclusion of colours (etc.) from the rank of external existences, there remains nothing, which external existences, there remains nothing, which can afford us a just and consistent idea of body.”can afford us a just and consistent idea of body.”

2727

The Attack on AbstractionThe Attack on Abstraction

Thus Berkeley and Hume attack Locke on Thus Berkeley and Hume attack Locke on the grounds that we can’t form a coherent the grounds that we can’t form a coherent idea of matter without using ideas of SQs.idea of matter without using ideas of SQs.

They see Locke as illegitimately trying to They see Locke as illegitimately trying to “abstract” a purely PQ idea of body away “abstract” a purely PQ idea of body away from our actual idea which is inextricably from our actual idea which is inextricably bound up with perceptual notions.bound up with perceptual notions.

Hence their focus on abstraction (see the Hence their focus on abstraction (see the Introduction to Berkeley’s Introduction to Berkeley’s PrinciplesPrinciples).).

2828

The Case for IdealismThe Case for Idealism

Berkeley concludes fromBerkeley concludes fromthis argument that bodiesthis argument that bodiesindependent of mind areindependent of mind areliterally inconceivable.literally inconceivable.

If this works, it seems toIf this works, it seems toshow that the only way weshow that the only way wecan make sense of thecan make sense of theworld is as fundamentally consisting of world is as fundamentally consisting of mentalmental entities (i.e. “spirits” and “ideas”. entities (i.e. “spirits” and “ideas”.

2929

““Something I Know Not What”Something I Know Not What”

To defend realism we should accept our idea To defend realism we should accept our idea of body as “inadequate” – we can’t conceive of body as “inadequate” – we can’t conceive of what it is that fills space except in terms of of what it is that fills space except in terms of “what it does” (cf. Locke, “what it does” (cf. Locke, EssayEssay II xxiii 2). II xxiii 2).

More modern concepts such as More modern concepts such as massmass and and electric chargeelectric charge make this clearer: we are make this clearer: we are under no illusion that the basic properties under no illusion that the basic properties employed in our scientific theories have to employed in our scientific theories have to be directly perceivable, or understandable in be directly perceivable, or understandable in non-dispositional terms.non-dispositional terms.

3030

Berkeley’s InstrumentalismBerkeley’s Instrumentalism

Immaterialism might seem to undermine Immaterialism might seem to undermine physical science, but Berkeley (following physical science, but Berkeley (following Newton) advocated instrumentalism:Newton) advocated instrumentalism:– The aim of science is to discover “laws” that The aim of science is to discover “laws” that

generate true predictions about phenomena.generate true predictions about phenomena.

– It is irrelevant whether the theoretical entities It is irrelevant whether the theoretical entities (e.g. forces) invoked have any real existence.(e.g. forces) invoked have any real existence.

– God benevolently arranges the observed God benevolently arranges the observed phenomena to follow these patterns, as “signs” phenomena to follow these patterns, as “signs” to enable us to direct our lives.to enable us to direct our lives.

3131

David Hume, 1711-76David Hume, 1711-76

Newton is right to insist Newton is right to insist that science can be done that science can be done without intelligibility.without intelligibility.

Gravity is “unintelligible”, Gravity is “unintelligible”, but but mechanicalmechanical causation causation is equally unintelligible.is equally unintelligible.

The aim of science is to describe things’ The aim of science is to describe things’ observed behaviour as simply as possible, in observed behaviour as simply as possible, in terms of the fewest possible causes.terms of the fewest possible causes.

3232

Hume on Science – NegativeHume on Science – Negative

In advance of experience, we cannot know In advance of experience, we cannot know anythinganything about what causes what. about what causes what.– So experience is So experience is our only basisour only basis for making for making

predictions about the unobserved.predictions about the unobserved.

All inference from experience is based on All inference from experience is based on the assumption that we can extrapolate the assumption that we can extrapolate from observed to unobserved (“induction”).from observed to unobserved (“induction”).– But this assumption has But this assumption has no rational no rational

foundationfoundation whatever! The basis of our reason whatever! The basis of our reason is animal instinct rather than angelic insight.is animal instinct rather than angelic insight.

3333

Hume on Science – PositiveHume on Science – Positive

The Foundation of Inductive ReasoningThe Foundation of Inductive Reasoning– Scientific (like all empirical) reasoning is Scientific (like all empirical) reasoning is

founded not on insight, but on a brute founded not on insight, but on a brute assumption assumption that the future will resemble the that the future will resemble the pastpast, for which no solid basis can be given., for which no solid basis can be given.

Good and Bad ReasoningGood and Bad Reasoning– But this doesn’t mean that all inductive But this doesn’t mean that all inductive

reasoning is equally good (or bad). The wise reasoning is equally good (or bad). The wise thing to do is to thing to do is to reason consistentlyreason consistently with this with this irresistible brute assumption.irresistible brute assumption.

3434

Example: MiraclesExample: Miracles

Why Do I Believe a Miracle Report?Why Do I Believe a Miracle Report?– Because I have Because I have experienceexperience that reports of that reports of

witnesses tend to be true. My belief is based witnesses tend to be true. My belief is based on inductive extrapolation.on inductive extrapolation.

Why Shouldn’t I Believe a Miracle Report?Why Shouldn’t I Believe a Miracle Report?– Typically, the inductive evidence Typically, the inductive evidence againstagainst any any

miracle will be far stronger than the inductive miracle will be far stronger than the inductive evidence in favour. I have lots of experience evidence in favour. I have lots of experience of people being mistaken, misled, tricked …of people being mistaken, misled, tricked …

3535

Immanuel Kant (1783)Immanuel Kant (1783)

Hume Hume has to behas to be wrong, wrong, because we have clear because we have clear examples of “synthetic examples of “synthetic a a priori”priori” knowledge: truths knowledge: truths

about the world knowable independently of about the world knowable independently of experience, that we see experience, that we see had to behad to be that way: that way:– Metaphysical principles (e.g. universal causation)Metaphysical principles (e.g. universal causation)– Euclidean geometry (e.g. Pythagoras’ theorem)Euclidean geometry (e.g. Pythagoras’ theorem)– Newtonian mechanics (e.g. conservation of Newtonian mechanics (e.g. conservation of

momentum).momentum).

3636

Hume’s Triumph!Hume’s Triumph!

Einstein’s General Relativity (1915)Einstein’s General Relativity (1915)– Space is gravitationally “curved”Space is gravitationally “curved”– So Euclid’s axioms probably aren’t true, and So Euclid’s axioms probably aren’t true, and

they’re certainly they’re certainly notnot knowable knowable a prioria priori..

Quantum Mechanics (1925)Quantum Mechanics (1925)– Fundamental particles don’t work at all as we Fundamental particles don’t work at all as we

(or Newton) would have expected: their (or Newton) would have expected: their behaviour is behaviour is describabledescribable, but , but notnot “intelligible”. “intelligible”.

– Randomness seems to be ubiquitous (though Randomness seems to be ubiquitous (though this would surprise both Hume and Kant!).this would surprise both Hume and Kant!).