berkeley and molyneux on retinal images

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Berkeley and Molyneux on Retinal ImagesAuthor(s): Colin M. TurbayneSource: Journal of the History of Ideas, Vol. 16, No. 3 (Jun., 1955), pp. 339-355Published by: University of Pennsylvania Press

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2/18

BERKELEY AND MOLYNEUX

ON RETINAL

IMAGES

BY

COLIN

M.

TURBAYNE

As

a

philosopher, Berkeley

had

many purposes.

The central

ones

were

to

refute

the

scepticism

inherent

in the

Newtonian

world,

to

criticize

the innovations

of the

philosophers,

natural

philosophers

and

mathematicians,

and to

demonstrate,

in

opposition

to

the

deistic

view

of a

distant

Deity,

the immediate

presence

of

God.

Berkeley

saw

that

the

chief

source

of

the

scepticism,

errors and

perplexities

beset-

ting

men's

minds

was the

prevailing

belief,

shared

by

the

common

man

and the

philosophers,

that

there are

material

entities

or

external

objects which are capable of existing whilst unperceived by any minds.

This

belief was an

essential

part

of

the doctrine which

Berkeley

called

materialism.

It

is

likely

that

Berkeley

was a

convinced

imma-

terialist

before he

wrote

the

Essay

Towards a New

Theory

of

Vision,1

and

even

before he

began

to

fill

his two

private notebooks,

now

called

the

Philosophical

Commentaries,2

but

it seems that

when

he

began

the

Commentaries,

he

had

found

neither

arguments

to

support

his

conviction,

nor

answers to

possible objections.

By

the

time

he

began

to write the Principles of Human Knowledge,3 he had found his argu-

ments,

and

knew

how

to

answer all

the

objections

to

immaterialism

that

he

could think

of.

One

important

objection

constitutes

the

Third

Objection

in

the

Principles.

This is

based

on

the

facts of

vision: .

. .

we

see

things

actually

without or

at

a

distance from

us,

and

which

consequently

do not

exist in

the

mind.

4

Consideration

of

this

difficulty

gave

birth

to

the

Essay.5

The

above

objection

was

the

view of

the

common man.

He

thought

that

external

objects

can

be directly seen. The philosophers, e.g., Locke, Malebranche and

Descartes,

corrected this

mistake

of

the

vulgar,

and

asserted that

external

objects

can

be

seen

only

mediately

or

indirectly by

means of

certain

immediate

objects

of

sight

which

do not

exist

outside the

mind

and

which

are

images

or

resemblances

of

external

things.6

Berkeley

felt

that

if

the

views

either

of

the

common

man

or

of

the

philosophers

were

correct,

then

immaterialism

was

impossible.

In

the

Principles,

Berkeley

indicates what

the

Essay

had

accom-

plished.

It had shown that:

.

.

.

the

proper

objects

of

sight

neither

exist

without the

mind,

nor

are

the

images

of

external

things.7

Published

1709.

Hereafter

referred o

as

Essay.

2Written

circa

1707-08.

So

named

by

A.

A.

Luce

in

his

Editio

Diplomatica

(Edinburgh,

1944).

Hereafter

referred

o

as

Com. or

Commentaries.

3

Published

1710.

Hereafter

referred

o as

Prin.

or

Principles.

4Prin.,

42.

5Ibid.,43.

6

Cf. Prin., 56. Ibid., 44.

339

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3/18

340

COLIN

M.

TURBAYNE

This

passage presents,

on

Berkeley's

considered

view,

two

important

conclusions

of the

Essay

and,

it

would

seem,

the two

important

con-

clusions

concerningvision,

from

the

standpoint

of the

metaphysicsof

the

Principles.

The

first conclusionwas

intended to answer

the

ob-

jection

of

the

common

man. The

second,

that

the

proper

objects

of

sight

are not the

images

of external

things,

was

intended to

refute

the

doctrine of

the

philosophers.

On

my

view,

Berkeley,

while

working

on

the

psychology

of

vision,

made

a

unique

discovery

which

was

not

only

far

out of

the common

road for that

subject,

but

which

was

also of

paramount

importance

to

his

metaphysics,

enabling

him

to

reach the conclusionwhich undermined he doctrine of the philoso-

phers.

I

hope

to

show

what that

discovery

was and

to

present

the

steps

which

led

Berkeley

to

it.

The

explicit

design

of

the

Essay,

however,

is

not

to

establish

the

two

conclusions

mentioned

above.

Berkeley

says:

My

design

is

to

show

the

manner

wherein we

perceive

by

sight

the

distance,

magni-

tude,

and

situation of

objects;

also

to

consider

the

difference

here

is

betwixt

the

ideas of

sight

and

touch,

and

whether

there be

any

idea

commonto both senses. Accordingly, he argumentis expressed n

the

four

main

divisions of

distance,

magnitude,

situation

and

hetero-

geneity.

The two

important

conclusions

(from

the

standpoint

of

the

Principles)

are

proved

in

the

divisionon

distance

and the

division on

situation,

respectively.

Throughout

the

Essay,

Berkeley

is

not

concerned to

deny

the

existence

of

external

objects.

He

seeks

to

establish

what

might

be

called

an

immaterialism

only

of

vision.

He

distinguishes

two

kinds

of objectsof sight.8 By mediationof the proper,primaryor immedi-

ate

objects,

which

are

colors,

we

are

able

to

perceive

the

secondary,

mediate

or

improper

objects

of

sight.

The

latter

are what

we nor-

mally

say

we see.

Whenever

we

say

that

something

we

see is

far

or

near,

big

or

small,

high

or

low,

we refer to

these

objects.

In

the

Essay,

Berkeley

regards

he

secondary

objects

of

sight

as

instances

of

tangible

objects.9

Moreover,

he

identifies

them

with

external, i.e.,

material

objects

in

external

space.10

Although

Berkeley's

theory

of

vision

was

subsequently

to

become

the

accepted

theory,

the

publication

of

the

Essay

drew

little

atten-

8

Essay,

50,

51.

9

Ibid.,

50,

where

he

states

that

they

properly

belong

to

touch.

See

also

46,

99,

117,

etc.

llIbid.,

111,

117,

etc.

See

also

Prin.,

43:

For

that

we

should

in

truth

see

external

space,

and

bodies

actually

existing

in

it,

some

nearer,

others

farther

off

....

11T.

K.

Abbott, Sight

and

Touch

(1864),

p.

1,

writes:

If

we

were

challenged

to

point

out a

single discovery

n

mental sciencewhichis universallyadmitted,we

should

at

once

name

the

Theory

of

Vision

of

Bishop

Berkeley.

Its

success

has

been,

indeed,

extraordinary.



4/18

BERKELEY

AND

MOLYNEUX ON

RETINAL

IMAGES

341

tion.

Nevertheless,

there was at

the time a

widespread

interest

in

the

subject

of

vision.

Berkeley's

two main authorities

were

Molyneux

and Malebranche. To the former's Dioptrica Nova (1692) and the

latter's Recherche de la

Verite

(1674)

he owed

much,

although

he

never

acknowledged

his debt

to

Malebranche.

Molyneux's

work

was

his

point

of

departure.

Berkeley regarded

it

as

an

expression

of

the

received

view

on

such

subjects

as

dioptrics,

anatomy,

the manner

by

which

we

see

things

at

a

distance,

and

the

problem

of

retinal

images.

From

Malebranche's

Recherche,

it

appears

likely

that

Berkeley

(as

well

as

Molyneux)

obtained

valuable information on

the

treatment

of distance and

magnitude.

Other

writers of

optics,

whom

Berke-

ley

studied

carefully,

were

Newton,

whose

Opticks

had

only

recently

been

published

(1704),

Isaac Barrow

12

and Descartes.13

In

spite

of

their

differences,

the writers

of

optics

shared

two

features

which

Berkeley by

his

genius

avoided,

and

thereby

not

only

created

a

new

subject

but

proposed

a

new

theory.

First,

the

writers

of

optics

confused

the

psychology

of

vision with

geometrical

optics

and

anatomy. Molyneux's Dioptrica

Nova

is

representative, al-

though

it did

take

advantage

of

the

New

Philosophy.l4

In

his

treat-

ment of

how

we see

things

at

a

distance,

Molyneux

mixed

psycho-

logical

and

geometrical

explanations.

For

example,

he

said that

the

distance

of

near

objects

is

perceived

by

the

turn

of

the

eyes,

or

by

the

angle

of

the

optic

axes.

15

Malebranche

mixed

the

categories

in

exactly

the

same

way.16

Turning

the

eyes

in

or

out is

experienced,

but

the

accompanying optic

angle

is

an

abstraction.

Berkeley

was

not opposed to geometrical optics, just as he was not opposed to

physics.

As he

was later

to

indicate

that

such

useful

entities

as

gravity

and

attraction

are

mathematical

hypotheses,

and

not

any-

thing

really

existing

in

nature,

17

so he

says

in

the

Essay

that,

al-

though

they

are

useful,'8

lines

and

angles

have

no

real

existence

in

nature,

being

only

an

hypothesis

framed

by

the

mathematicians.

19

He

saw

that

just

as

children

and

idiots,

although ignorant

of

the

laws

12

Lectiones

Opticae

et

Geometricae

1669).

13

Dioptrique

(1637);

first Latin

edition

(1644).

14

William

Molyneux

(1656-1698),

who like

Berkeley

attended

Trinity

College,

Dublin,

was

a

champion

of

Locke.

He

speaks

highly

of

him

in

the

dedication.

Locke's

Essay

was

introduced

by

him

to

Trinity

College

before

Locke

was

known

at

either

Oxford

or

Cambridge.

He

and

Locke

frequently

corresponded

n

the

nine-

ties.

They

became

close

friends,

although

they

met

only

once,

shortly

before

Moly-

neux's

death.

See

Locke,

Some

Familiar

Letters

.

.

.

(1706).

15

Op.

cit.,

113,

my

italics.

16

Op.

cit.,

I.

ix.

3,

in

his

statement

of

the

first of

the

six

means

for

judging

distance.

17Siris, 234. 1878. 1914.



5/18

342

COLIN

M.

TURBAYNE

of

physics,

can feel

that

a rock is

heavy

or

light,

so

they

can see

things

far or

near

without

knowing

the

principles

of

geometrical optics:

an

obvious truth which the opticians, in their zeal to geometrize

vision, ignored.

However,

some of them did

hint at

a new

approach.

Barrow

said that

the

received

principles

were

inadequate.20 Molyneux

said that

some

problems

demanded

enquiry

into

the

soul's

faculties;

which

is not the

proper

subject

of

this

discourse.

21

Berkeley clearly

distinguished

his

own

subject

from

optics, geometrical

optics, diop-

trics,

catoptrics

and

anatomy,

albeit

regarding

it as

a

part

of

phi-

losophy:

To

explain

how

the

mind

or

soul

of man

simply

sees is one

thing,

and

be-

longs

to

philosophy.

To consider

particles

as

moving

in certain

lines,

rays

of

light

as

refracted or

reflected,

or

crossing,

or

including angles,

is

quite

another

thing,

and

appertaineth

o

geometry.

To

account for the

sense

of

vision

by

the mechanism

of the

eye

is

a third

thing,

which

appertaineth

o

anatomy

and

experiments.22

Thus, although

he

asked

the same

question

as his

precursors,

How

do we come to see things in space? he tried to answer it in terms

only

of

what

we

actually

experience.

In

confining

himself to

these

terms,

Berkeley

delineated

the

boundaries of

a new

subject

and

thereby

provided

a

significant

philosophical

advance.

Secondly,

in their answer to

the

above

question,

the

essential

doc-

trine of

the writers

of

optics

was that

the

act of

seeing

is an

act

of

judgment.

This was a

Cartesian

view.

Descartes23

and Male-

branche

24

used the

verb

juger.

Molyneux

said that

the

manner

by

which we see

things

at a distance is rather the act of our

judg-

ment,

than of

sense.

25

Such an

act

of

judgment

involves

the

pres-

ence

of a

necessary

connexion,

and

therefore,

of

ideas held

in

common,

between

the

objects

actually

intromitted

by

the

eye

and

those

ob-

jects

which

we

ordinarily

see

in

space.

Berkeley

noted

that

the

writers of

optics

imagined

that

we

see

things

in

the

same

way

as we

reach

a

conclusion in

mathematics,

betwixt

which

and

the

premises

it is

indeed

absolutely

requisite

there be

an

apparent, necessary

con-

nexion. 26

Thus,

on

this

view

we

judge

of

the

near

distance

and

situation

of

things

outside us

by

a

kind

of

innate

geometry,

27

just

as

a

blind

man

would

be

able,

by

holding

two

crossed

sticks,

one

in

20

He

looked

forward o

the

time

when

the

manner

of

vision is

more

perfectly

made

known.

Quoted

n

Essay,

29.

21

Op.

cit.,

105.

22

The

Theory

of

Vision

Vindicated

and

Explained

(1733),

43.

Hereafter re-

ferredto

as

the

Vindication

r

T.V.V.

23

Op.

cit.,

VI.

24

Op.

cit.,

I.

ix. 3.

25

Op.

cit.,

113.

26

Essay,

24.

27

Ibid.,

appx.



6/18

BERKELEY

AND

MOLYNEUX

ON

RETINAL

IMAGES

343

each

hand,

to

judge

of the distance

and

situation

of

objects.28

On

the denial

of

all

this,

Berkeley's

whole

theory depends.

29

He agreedwith the writersof optics that the properor primaryob-

jects

of

sight

are

colors

at

no

distance

off.30

He

agreed

that

we

do

in

fact see

bodies

in

space,

some

near,

others

farther off.31

We

have

seen

that

he

called

these

secondary

objects

of

sight,

that he

regarded

them

as

instances of

tangible

objects,

and

that

in

the

Essay

he

as-

sumed

them to

be

identical

with

external

or

material

objects.32

He

agreed

that

the

problem

was

to

discover

how

we come to see

bodies

in

space,

when

colors

only

are

intromitted

by

the

eye.

At

this

point,

Berkeleyand the writersof optics diverged. The latter assumedthat

the

connexion

between the two

sorts

of

objects

is

necessary,

because

they

own

identical

properties

such as

shape,

size

and

situation.

Berkeley

saw

that

if

this

were

true,

a man

born

blind

and

made

to

see,

would

be

able

to

recognize

bodies

in

space

by sight

alone.33

After

reflection,

Berkeley

concluded

that

such a

feat would

forever

lie

be-

yond

his

attainments.

The

once-blind

man

would

come

to

recognize

bodies

in

space

only

after

painstaking

experience

nvolving

the

con-

stant and

long

associationof

ideas of

touch

and

sight.

It

seems to

me

almost

certain

that

Berkeley

found

the

clue

for

this

important

conclusion

rom

the

works

of

neither

of

his two

main

authorities,

but

from

a

certain

jocose

problem

which

Molyneux

sent

in

a

letter

to

Locke

in

1693.34

Locke

published

t

as

follows:

Suppose

a

man

born

blind,

and

now

adult,

and

taught

by

his

touch

to

dis-

tinguish

between

cubeand

a

sphereof

the

same

metal,

and

nighly

of

the

samebigness, o as to tell, whenhe felt one andthe other,whichis the

cube,

which

the

sphere.

Suppose

hen

the

cube

and

sphereplaced

on

a

table,

and

the

blind

man

to

be

made

o

see;

quaere,

Whether

by

his

sight,

before

he

touched

hem,

he

could

now

distinguish

nd

tell

which

s

the

globe,

which

the

cube?

35

28Cf.

Malebranche,

p.

cit.,

I. ix.

3,

. ..

un

aveugle

...

pourrait

par

une

espece

de

geometrie

naturelle,

uger

a

pen

pres

de la

distance

de

quelque

corps

....

Des-

cartes'

expression

s:

ex

geometria

quadam

omnibus

nnata, quoted

by

Berkeley,

ibid.

29

Essay,appx.

3lIbid.,

43,

50;

T.V.V.,

42.

Cf.

Malebranche,op.

cit.,

I.

ix.

3,

Nos

yeux

nous

les

representent

outes

dans

une

meme

distance, quoiqu'il

soit tres

raisonnable

d'en

croire

quelques-unes

eaucoup

plus

6loign6es

de

nous

que

les

autres.

3

See

above,

note

10.

32

See

above,

text

to

notes

9

and 10.

33

T.V.V.,

44.

34

See

Locke,

Fam.

Letters.

Molyneux

writes,

Mar.

2nd,

I

have

proposed

[it]

to

divers

very

ingenious

men,

and

could

hardly

ever

meet

with

one,

that

at

first

dash

would

give

me

the

answer

to

it

which

I think

true

till

by

hearing

my

reasons

they

were

convinced.

Locke

replied

immediately,

Mar.

28,

Your

ingenious

problem

will

deserveto

be

published

o

the world.

5

Essay

Concerning

Human

Understanding,

nd ed.

(1694),

II.

ix.

8.



7/18

344 COLIN M.

TURBAYNE

None of the

writerson

optics

whom

we are

considering, xcept

Moly-

neux,

has

provided

us

with an

answer o this

problem,

but the

affirma-

tive solution

subsequently

ventured

by

Leibniz

36

doubtlessindicates

what theirs would be.

Locke and

Molyneux

answered

n

the

nega-

tive.37

Berkeley agreed,

but

gave

to their answer

a

significance

which

they

missed. From

his view that

the once-blindman

would

never

be

able to

make

such

an

elaborate

nference

as

Leibniz

supposed,

Berke-

ley

inferred hat

we

cannot see

bodies

n

space

(i.e.,

secondaryobjects)

until

we

have

touched

some

of

them

while we look.

He

was,

accord-

ingly,

able

to

deny

the common

errour

of the

opticians

that there

is

a

necessary

connexionbetween

the

primary

and

secondaryobjects

of

sight;

to

deny

that

they

have identical

properties

such as

shape

and

size,

even

though

they

share

identical

names,

and to

deny

that we

see

by

means of

lines

and

angles.

He asserted

that the

connexionbe-

tween

the

primary

and

secondary

objects

of

sight

is

learned,

the

former

objects

suggesting

the

latter.38

The

heterogeneity

of

sight

and

touch

was

the main

part

and

pillar

39

of

Berkeley's heory

of

vision.

It distinguishedhis theoryfrom all preceding heories. He appliedit

to

all

the

problems

of

vision,

including,

as we

shall

see,

the

tantalizing

problem

of

the

inverted

retinal

image.

The

two

important

conclusions

regarding

vision,

from

the stand-

point

of

the

metaphysics

of the

Principles,

established

n

the

Essay,

were

(to

repeat):

(1)

The

properobjects

of

sight

do not exist

without

the

mind; (2)

The

proper

objects

of

sight

are

not the

images

of

ex-

ternal

things.

Berkeley

need

not have

proved

the first of

these,

be-

cause it was the

accepted

view of

the

philosophers.40

The

second

is

uniquely

Berkeley's.

It is

contrary

o

the essential

doctrine,

not

only

36

Leibniz,

Nouveaux

Essais

(1765),

II.

ix.

8,

maintained

hat

there

are

elements

common

to

the

two sets of

experiences,

e.g.,

shape,

and

concluded

that

the

once-

blind

man

could

distinguish

he

cube

and

sphere

by

the

principles

of

reason,

com-

bined

with

what

sensuous

knowledge

he

has

previously

acquired

by

touch,

though

not

perhaps

immediately.

He

argued

that

we all

have

rudiments of a

natural

geometry,

and

that the

above

feat

could be

performed

by

dint of

reasoning

about

rays according to the laws of optics (my italics). 37

Molyneux's

answer

was,

of

course,

ncompatible

with

the

doctrine

which

dominates

his

earlier

Dioptrica

Nova,

but I

have no

evidence

that he

noticed

this.

38

It is

sometimes

held

that

Berkeley

meant that

the

passage

from

the

proper

objects

of

sight

to

external

objects

is

of the

nature of

judgment

or

inference.

He

does

sometimes

use

the

word

judgment,

but when

he

seeks

precision,

e.g., Essay,

50;

T.V.V.,

42,

his

term

is

suggestion.

39

T.V.V.,

41.

40

See

Locke,

op.

cit.,

II.

viii.

8; 13;

Malebranche, p.

cit.,

Reponse

a

M.

Regis:

Je

suppose

comme

une

verite

incontestable

que

les

couleursne

sont

point

repandues

sur les objets,mais qu'ellessont uniquementdans 'ame.



8/18

BERKELEY

AND MOLYNEUX ON

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IMAGES

345

of

the

philosophers,41

but,

as

we shall

see,

of

the

writers

of

optics.

It

is

proved

n the

Essay

as

a

by-product

of

his

treatment

of the

problem

of

the inverted

retinal

image

at

the

end

of the

division on

situation.

Sections 88-120 of the Essay constitute one of the most subtle and

profound

passages

in

Berkeley's

writings.

The

remark of

Thomas

Reid

about the whole

Essay

is

appropriate

to

this

division:

He

seems,

indeed,

to

have exerted

more

force of

genius

in this than

in

the

main

branchof his

system.

2

It

is a

masterpiece

of the

procedure

of

insinuating

the truth

by

degrees.43

Statements made at

the outset

as

though true,

are

not

denied until

the

close,

and even

then,

the

whole

truth

(as

Berkeley

sees

it)

is

suggested

rather

than

stated.

Berkeley

presents

the

problem:

There

is

at

this

day

no

one

ignorant

that the

pictures

of

external

objects

are

painted

on

the

retina,

or fund

of

the

eye:

That we

can see

nothing

which

is

not

so

painted.

.

. .

But

then

in

this

explication

of

vision there

occurs

one

mighty

difficulty.

The

objects

are

painted

in

an

inverted

order

on

the

bottom

of

the

eye

....

Since

therefore

the

pictures

are

thus

inverted,

it

is

demandedhow

it comes

to

pass

that we

see the

objects

erect and

in

their

natural

posture?

44

In

the above

passage,

we must

distinguish

Berkeley's presentation

of

the

general

theory

regarding

retinal

images:

that

they

are

images

of

external

objects,

from

his

treatment of

the

difficulty

embodied

in

this

theory:

that we

see

objects

erect,

although

their

images

are in-

verted on the

retina.

Berkeley

first

treats

the

subsidiary

problem:

How

do

we see

things

erect

when

their

images

are

painted

inverted on

the

retina?

He

con-

siders the traditional solution, which according to

Molyneux

is al-

lowed

by

all

men

as

satisfactory.

45

He

summarizes

Descartes' ac-

count,

but

Molyneux's

has

almost

identical

features:

The

mind

takes

no

notice

of

what

happens

to

the

rays

in

the

eye

by

refraction

or

decussation,

but

.

.

.

hunts back

by

means

of

each

pencil

of

rays

to

the

source

in

the

upper

or

lower

part

of

the

object.46

There

is

the

41

See

Locke, op. cit.,

II.

viii.

8-15.

His

official

view

was

that

our

ideas

of

pri-

mary qualitiesexactly resemble he primaryqualitiesof externalobjects. See also

Malebranche,

op.

cit.,

VIe

Zclaircissement.

He

concluded,

through

revelation,

though

not

by

reason,

hat

there

is

actually

outside us

an

external

world

resembling

that

which

we see.

42

Essay

on the

Powers

of

the

Human

Mind,

I,

230.

43This

procedure

s

most

marked

in

the

Essay,

which

is

a

half-way

house to

immaterialism,

ut

it

is,

in

fact,

the

manifestationof

a

maxim

of

Berkeley's:

He

that

would

bring

another

over to

his

opinion,

must seem

to

harmonizewith

him

at

first,

and

humourhim

in his

own

way

of

talking

....

Commonplace

Book,

from

Fraser,

Works,

,

92.

Not

included

n

the

Commentaries

s

edited

by

Luce.

44

Essay,

88.

45

Op.

cit.,

289.

46

Ibid.,

my

italics.



9/18


10/18

BERKELEY

AND

MOLYNEUX

ON RETINAL

IMAGES

347

representation

is there

perceived

by

the sensitive

soul

....

We

are

likewise

to

observe,

that

the

representation

of the

object

on the fund

of the

eye

is

inverted.49

Newton's

account,

in the

Opticks,

is

similar. 0

Berkeley

held

that

the

accepted

view

was not

only

that

pictures

or

images

on

the retina

are

inverted

and

copy

external

objects,

but

that

they

are

the

proper

or

immediate

objects

of

sight.51

At

the end

of

the

division,

Berkeley

gives

his

final

solution

(for

the

Essay)

to

the

problem

of

the

inverted

retinal

image.

At

the

same

time,

he

throws

doubt

upon

all

the

features of

the

accepted view re-

garding

retinal

images,

and

proves

that

the

proper objects

of

sight

are

not

the

pictures

of

external

objects.

He

begins

by

accepting,

for

the

time

being,

an

important

assumption

of

the

writers of

optics:

Let

us

suppose

the

pictures

in

the

fund of

the

eye

to

be

the

immediate

objects

of

sight.

52

He then

presents

the

key

to his

remarkable

in-

sight

upon

the

whole

subject

of

retinal

images:

Farther,

what

greatly

contributes o

make

us

mistake in

this

matter

is

that

when we think of the pictures in the fund of the eye, we imagine ourselves

looking

on

the

fund

of

another's

eye,

or

another

looking

on

the

fund

of

our

own

eye,

and

beholding

he

pictures

painted

thereon.53

This

is

the

root

cause

of

the

delusion

to

which

not

only

the

writers

of

optics

in

Berkeley's

day

were

prone,

but into

which

we

all

fall.

Not

even

Newton

escapes:

For

anatomists,

when

they

have

taken

off

from

the

bottom

of

the

eye

that

outwardand most thick coat called the Dura Mater, can then see through

the

thinner

coats,

the

pictures

of

objects

lively

painted

thereon

(this

only

excepted,

hat the

pictures

shall be

inverted).54

In

what

follows,

Berkeley

uses

the

situation

proposed

by

Newton,

but

unlike

him,

avoids

the

attendant

delusion:

Suppose

two

eyes

A

and

B;

A

from

some

distance

looking

on

the

pictures

in

B

sees

them

inverted,

and

for

that

reason

concludes

they

are

inverted in

B.

49pp. 104-105.

50

I.

.

vii.

Light

which

comes

from

the

object

shall

illuminate...

and

thereby

make

a

picture

like

the

object

in

shape

and

colour,

this

only

excepted,

that

the

picture

shall

be

inverted.

He

does

not

state

that the

pictures

on

the

retina

are

perceived

by

the

sensitive

soul,

but he

goes

on

to

say

that

these

pictures

...

are

the

cause

of

vision.

51

See

T.V.V.,

50,

where

he

states

that

the

view

that

retinal

mages

are

the

proper

objects

of

sight,

is

vulgarly

supposed

by

the

writers

of

optics.

52

Essay,

114.

53

Ibid.,

116,

my

italics.

54

Opticks,I. 1.vii.



11/18


12/18

BERKELEY

AND MOLYNEUX

ON

RETINAL IMAGES

349

but

he does

not mean those

things

painted

on the retina which

can

be

seen

after removal

of the dura

mater

from an

eye.

He

does

not

mean

any

such

secondary

objects.

He means retinal

images

con-

sidered as the

primary

or immediate

objects

of

sight.

They

cannot

be

seen in the normal

sense

of

see.

The

eye

B sees

only

what

is

represented

by

the

little

pictures

in

A.

They

are

all

B

sees,

in

the

strict or

primary

sense

of

see.

Although

the writers

of

optics

intended

to

distinguish

the

primary

from

the

secondary

objects

of

sight, they

nevertheless

thought

that

the former

could be

seen.

In

fact, therefore, by giving

to

retinal

images

characteristics

belonging

to

secondary

objects,

they

confused

them.

Secondly,

from

the fact

that we

can see

inverted retinal

images

in

another

eye,

we cannot

correctly

conclude

that

the

proper

objects

of

sight

are

inverted. To

do

so is

again

to

confuse

the

secondary

with

the

proper

objects

of

sight.

As

Berkeley

states

it,

the

eye

A,

look-

ing

on the

pictures

in B

sees

them

inverted,

and

for

that

reason con-

cludes

they

are inverted in

B;

But this is

wrong.

The

writers

of

optics fell into the same error. The cause of their delusionwas that

they

forgot

that

while

looking,

they

were

looking through

an

inverting

lens.

In

Berkeley's

example,

what

A

sees

on

B's

retina,

cannot be on

B's

retina because

of

the

inverting

lens

which

A

wears.

Thus,

if

reti-

nal

images

are

secondary

objects

of

sight,

then

they

are

inverted.

But

if

they

are

regarded

as visible

primary

objects,

then

they

are

erect.

Thirdly,

retinal

images

or

pictures

are

so-called,

because

when

we

consider

hem,

we

always

imagine

a

situation,

similar

to

that

proposed

by Newton, and analyzedby Berkeley. We imagineourselves look-

ing

on

the

fund

of

another's

eye,

or

another

looking

on

the

fund of

our

own

eye

and

beholding

the

pictures

painted

thereon.

We call

them

pictures

or

images

because we

notice

they

exactly

copy

larger,

so-called

originals.

Fourthly,

if

the

assumption

of

the writers

of

optics,

that

retinal

images

or

pictures

on

the retina

are

the

properobjects

of

sight,

is

up-

held,

then

we

can

see

(strictly

speaking)

nothing

but our

own

pictures

which we must compare,not with external objects, but with other

pictures

of

our

own.

As

Berkeley

states

it

in

the

forementioned

xam-

ple,

the

eye

B

sees

only

what

is

represented

by

the

little

pictures

in

A,

while

for

the

eye

A,

the

archetypes

are

not

things

existing

with-

out,

but

the

larger

mages

projected

on

its own

fund.

These

passages

embody

two

closely

connected

conclusions

which

(on

my

view)

mani-

fest

Berkeley's

most

significant

discovery

in

vision:

We see

(strictly

speaking)

nothing

but our

own

pictures,

and:

The

archetypes

of

our

picturesareotherpicturesof our own.



13/18

350

COLIN

M.

TURBAYNE

If

this second

conclusion

s

true,

then

the

general theory

of

New-

ton,

Molyneux

and

the otherwriters

of

optics

regarding

etinal

images,

which

Berkeley

stated at the

beginning

of the divisionon

situation,

is

false.

This was:

There

is at

this

day

no

one

ignorant

that

the

pic-

tures

of external

objects

are

painted

on

the

retina,

or fund

of

the

eye.

59

However,

f

pictures

on

the

retina

are

agreed

o

be the

proper

objects

of

sight,

then

it

follows

that

the

properobjects

of

sight

are

not

the

images

of external

things. This,

it will

be

recalled,

was one of

the

two

important

conclusions

which

Berkeley

n the

Principles

considered

the

Essay

had established.

Thus,

not

only

was

the

doctrine

of

the

writers

of

optics refuted,

but

also

the

doctrine

of

the

philosophers.60

One

important

factor

seems

to

nullify

Berkeley's

refutation

of

the

doctrineof the

philosophers.

It is

exceedingly

doubtful

whether

the

philosophers

assumed,

with the

writers

of

optics,

that

retinal

images

are

the

proper

objects

of

sight.

So

far,

Berkeley

has not

explicitly

denied

this

assumption.

Moreover,

f

it

is

required,

Berkeley's

meta-

physical

conclusion s

of doubtful

validity,

because retinal

images

are

suspiciouslylike external objects. However, on my view, Berkeley

did

not

believe that

retinal

images

are

the

properobjects

of

sight,

but

did

believe that this

important

metaphysical

conclusionstill

retained

its

truth.

First,

in

the

penultimate

section of

the division

on

situation,

Ber-

keley

appears

o

relinquish

he

assumption

hat retinal

images

are

the

proper

objects

of

sight:

. . . the visible eye, as well as all othervisible objects,hath been shownto

exist

only

in

the

mind,

which

perceiving

ts

own

ideas,

and

comparing

hem

together,

calls

some

pictures

in

respect

of

others.61

But

this is

not

conclusive,

and

Berkeley

does

not

seem to

want to

make an

explicit

denial.

Such

reticence is

in

line

with his

policy

of

insinuating

the

truth

by

degrees.

He has

already

clarified

the

am-

biguity

in

the

opticians'

use of

the

term

retinal

images,

by

show-

ing

that

it

may

refer

either

to

those

objects

which

we

can

actually

see,

i.e., secondaryobjects,or to those objectswhichwe cannotsee,

except

as

infants or

after

being

couched

or

blindness,

.e.,

primary

objects

of

sight.

There

is

really

little

need

for

him

to

provide

the

whole

truth

as he

sees

it,

for

the

Essay

is

a

work

on

vision,

and

he

has

refuted the

writersof

optics,

if

not the

philosophers,

without

doing

so.

But

there

is

little

doubt

that

Berkeleyregards

he

identification

of

the

two

kinds

59

See

above,

text to

notes

44,

49,

and

note

50.

60

See

above,

text

to

notes 7, 41.

61

Essay,

119.



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BERKELEY

AND MOLYNEUX

ON RETINAL

IMAGES

353

to the

years

of

Manhood,

When

he looks

up

or turns

up

his head he

shall

behold wt

we call

under.

Qu:

wt

would he think

of

up

& down?

70

Berkeley never directly answered his own question, and never used

this

device

of the

man

wearing

inverting spectacles

in

any

of

his

works. But the

implied

answer

to

the

question

is

that

for

such a

man,

the terms

up

and

down,

left

and

right

would

have

the

same

pragmatic

meanings

as

they

have

for

us.

If

he were

asked

to

point

to

the

moon,

he would

point

where we

point.

If

asked

to

paint

a

landscape,

he

would

not

need to

exhibit it

upside

down in

any

gal-

lery.

I

say

that

this

answer

is

implied

for two

reasons:

first,

because

of the

way Berkeley

wrote the

entry.

It is as if he were

saying:

The

vulgar

view is that

such

a

man

would

see the world

upside

down,

but

would

he

not

really

see

it

erect?

Secondly,

if

Berkeley

thought

that

such a

man

would

see

the

world

inverted,

then

his answer

would

be

contrary

to

the

whole

tenor of

his

account

of

situation

in

the

Essay.

This Pickwickian

problem

had

been

troubling

Berkeley

for

some

time.

Earlier

in

the

Commentaries,

he

had

posed

the same

problem

but

seemed

to be

ignorant

of

the answer.7

Suddenly,

it

seems,

the

correct

answer

came to him.

But this

answer

presupposes

in

Berkeley

that

knowledge

which

he

possessed

when

writing

the

closing parts

on

situation

in

the

Essay.

The

person

wearing

inverting

spectacles

from

birth

lives

constantly

with

his own

visible ideas

and with

nobody

else's.

Having

nothing

else

but

his own

visible

ideas with

which

to

compare them,

he

would

experience

no

more

difficulty

in

learning

to

see

than

any

other

child,

and

would

always

obtain

an

internally

cor-

rect

view of

the

world. He would determine the situation of the

things

he saw

in

relation

to his

own

constant set.

Berkeley

would

have

been

able to

provide

the

correct solution

to

this

problem

if

he

had

possessed

the

knowledge

which

he

had while

writing

on

the

prob-

lem

of

the

inverted

retinal

images

in

the

Essay.7

This

knowledge

is

70

Com.,

278.

71

See

Corn.,

148.

72

Apart

from

its

metaphysical

significance,

Berkeley's

solution

illuminates his

attitude to two theoriesdesigned o explainerect vision: the projection heory and

the

eye-movement

heory

(see

above,

note

48).

On the

former,

he

inverted

retinal

image

is

necessary

o

erect

vision.

Apparently

without

the

help

of

experiment,

he

produced

an

answer

incompatible

with

this

theory.

His

solution

amounts

to

the

theory

that

erect vision

is

independent

of

whatever

inversionsor

even

distortions

(as

long

as

there

is

uniformity)

the

rays

of

light

may

undergo

before

they

reach

the

retina.

For

example,

harmony

between

touch

and

sight

may

be

achieved

after

wear-

ing

either

inverting

or

pseudoscopic

perspectives.

(See

in

this

regard

G.

M.

Strat-

ton,

loc.

cit.,

above,

note

48.

Stratton's

experiment

proves

that

erect vision

may

be

re-acquired

n

an

adult

after

a

mere eight days of wearingan invertinglens.) On

the

eye-movement

heory,

the

felt

direction

of

the

turn of

the

eyes

is

the

test of



17/18

354

COLIN

M.

TURBAYNE

embodied

in what I

consider to be

Berkeley's

most

significant

dis-

covery

within

the

subject

of

vision.

That

Berkeley

himself

so

regarded

it is

strongly

indicated

by

the

fact

that it came

to him as

a result of his work

on that

problem

of

vision which he

held to be the most

fruitful,

albeit the most

difficult;

for, twenty-five

years

later,

he wrote:

The

solution

of

this

knot about

inverted

images

seems the

principal

point

in

the

whole

optic

theory,

the most

difficult

perhaps

to

comprehend,

but

the

most

deserving

of our

attention, and,

when

rightly

understood,

he

surest

way to lend the mind into a thorough knowledgeof the true nature of

vision.73

It is

strange

that,

in

spite

of the

emphasis

which he

placed

on

this

problem,

authorities

have

generally

neglected Berkeley's

treatment

of

it,74

and

have

tended to

regard

as

the main

point

of his

theory

the

doctrine

that

we do not see bodies

in

space

outside

us

(owning

size

and

situation)

immediately;

75

a doctrine

which,

in

fact,

was

the ac-

cepted

view

of

the

optical

writers

and

philosophers

who

preceded

Berkeley,

and which he took over from them. As we have

seen,

Berke-

ley's

discovery,

if

true,

shattered the over-all

theory

about

retinal

images

held

by

the

writers

of

optics.

But

the

factor which

gives

most

weight

to

my

view,

and

which,

had

it

been

noticed

by

authorities on

Berkeley's theory

of

vision,

might

have induced

them to

study

more

carefully Berkeley's

account

of

retinal

images,

is

this:

Berkeley's discovery

opened

the

way

for

his

subsequent

refutation of

the

prevailing metaphysical position

of his

situation.

Berkeley

vacillated on this

subject.

In the

Essay,

the test is the

experi-

enced motion

of

the

eye.

In the

Vindication,

it is the various

motions of the

head. It is

difficult to

discover

why

Berkeley

did not use the device of the man

wearing

inverting

perspectives

in the

Essay,

but the

way

in which he stated

the

facts: . .

.

when he looks

up

or

turns

up

his head

..

.

,

suggests

a reason. When

one looks

through

an

inverting

lens,

one must turn

up

the

eyes

in order to see

down,

but

one

must

turn

up

the

head

in order

to

see more

of

upper

objects.

Thus,

Berke-

ley,

who was

acquainted

with

inverting

lenses,

may

have seen

that the

performance

of a man wearing an inverting lens might disprove his eye-movement theory. At

any rate,

in

the

Essay,

he

kept

the

eye-movement theory

and

omitted to deal

with

the

confusing

subject

of

double

inversion.

In the

Vindication

he

had come to

rely

on more

massive muscular sensations such as head movements.

This

allowed

for

erect

vision

for

a man

wearing

an

inverting

lens,

even

though

he would turn

up

his

eyes

in

order

to

see down.

73

Vindication,

50.

74

A

prominent

exception

is

A.

A.

Luce, Berkeley

and

Malebranche,

Ch. II.

75

E.g.,

Samuel

Bailey,

A

Review

of

Berkeley's

Theory of

Vision

(1842);

cf.

Ch.

I; also T. K. Abbott, op. cit.



18/18

berkeley and molyneux on retinal images

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