earman - carnap, kuhn, and the philosophy of scientific methodology

8/11/2019 Earman - Carnap, Kuhn, And the Philosophy of Scientific Methodology

1/29


2/29

Carnap, Kuhn,and thePhilosophyof

Scientific Methodology

John

Earman

/

1

Introduction

For the past tw o decades logical positivismhas served as a w h i p p i n g

boy.

B y

e m p h a s i z i n g th e shor tcomings

of

this

failed

philosophical,

pr og r am, the v i r tues of the new

postpositiyist

pTi|osop_hy__of_sciencc

arc m a d e to seem more lustrous. It is, of course, n ot su r p r i s i ng to

f ind

such po lemica ldevices emp loyed , s ince they

are

c o m m o n

to

th e

rhetor ic of revo lu t ions ,

w h e th e r political, scientific,

or philosophical .

Or so the s t anda r d assessment wou ld go . W h a t I find askew in this

assessment is the not ion tha t a philosophical revolution asopposed

to

an

evo lu t i on

has

taken place. For a l though

I am no apologist for

logical posi t iv ism,

it

doessccoiJojme t h a t m a n y

ofthe t h e m e s f jJ T

so-called

postpositivist philosophyofjscicnccarcextensionsof ideas

f o u n d in the

wr i t i ngsoLCarnap

an d

other leading logical positivists

an d logicalemplficlstC^But m ypurposehere is not to

cont r ibute

to

a

revisionist history of philosophy. Rather , I aim to pay homage to

both Carnap

an d

K u h n

b y

noting some str iking similar i t ies

an d

also

some s t r ik in g di f ferences . Theses imilarities

an d

di f ferences

are

use-

ful

in helping to focus

some

of the

still

unresolved issues about the

n a t u r e of

scientif ic

methodology .

2 Logical Positivism, Logical Empiricism,,and

Kuhn's

Structure of Scientific

Revolutions

T he member s of

the

Vienna Circle often took votes on the issues

they

debated.

W h il e

I

have

n o

documen ta r y ev idence

to

of fer

of an


3/29

J o h n E a r m a n

ac lu a l

vole,

I am m o r a l l ycertain o f

what

the

rcsull

wo u ld

have been

fo r

ihc question,

Ver i f ica t ion

is a

relation between what

an d

w h a t ?

In x is verif ied by y, j&fs presumably a sentence. An d it istempting

to lake^jHo

be a

fact,stale

of

a f fa i r s ,

or

something

in

iheworldlhal

makes A C iruc

and can be

d i rec t ly ascertained.

But an

attempt

to

compare language

and

iheworld would have slruck iheCircle mem-

bers

as of a

piece w i th

the

metaphysics

thaiihe ver i f iab i l i ly principle

of meaning wassupposed lo

banish.Their a l t e r n a t i ve w as

lo

lake y

lo be another sentence, for then the relationjjctwecn x and yis an

.

unproblcmalic

logical

r c j a t i o n . _T h . 5

move, however,

seems

lo

leave

j

us in

ihc

same

metaphysical

th i cke l

since ver i f ical ion would seem

to

/

require thaiyis a true sentence, and is not a truesentenceone that /

corresponds to the facls?

The

escape lhat some

ofihe

circle members

soughlwas a

resort to

a

coherencetheory

of

truth. E v e n t u a ll y ,however, Carnap

abandoned

resort,

presumably

because

of a

combinalion

of

the

drawbacks

of

thecoherence account of truthand

the

allraclivenessof '

theory of truth. Bui w h a l I wish to emphasize here are ihe

qual i f i -

calions that Carnap put on any

talk

about comparing stalemenls

wi lh

facls. In

Truth

and Confirmation (1949) he

emphasized

lhat he

preferred lospeak of

confronling

slatementswilh facts:

There has

been

agood deal of dispute as to whether in ihc procedure

scientific

test ing

slatements must becompared

with

facts or as lo whe the r such

comparisons

be

unnecessary ,

if

nol impossible. If "comparison of s lalerncnl

wilh

fact"

m e a n s

ihc

p rocedure

which

we

called

ihc

firsl

opcralio^rylhcn

it

mus

be

adin i l lcd

lhal ihis

procedure

is nol

on ly

possible,

b ul

even indis-

pensable

for

scientific

testing. Y el

ilm u s

be remarked

lhal

ih c

fo rmula t ion

"comparison

of

s t a temen t

an d

fact"

is nol

unobjeclionable . First,

ihe

conccpl

"comparison" is not qu i l c appropr ia te here. T wo objecls can be compared

in regard lo a proper ly

which m

ir r j jarnr l n r j ~ r them in varia

We

ihcrefore

prefer lo speak of "cwnfronlalihH"

ra lhcr ihan^companso l

Confron ta t ion isun ders tood toconsX^jrjJiMnng out as to

fact

is

such

as isdescribed in

the

s ta tem ent , or, lo

express

it

differently ,

as

lo whe the r th e

s ta tement

is

true

to

fact.

(1949, 125)

Carnap then continued w i th a

passage

that might haveservedas an

advertisement for Kuhn's S t ruc t u re

o f

Scientific Revo lu t i ons .

Fur the rmore , ihc

formula l ion

in icrms of "comparison," in speak ing of

"facls" or

"realities"easily

Icmpts one inlo th e absolutislic

view

according lo


4/29

JJ

C a r n a p , K u l i n , an d

the

Philosophyof Scientific

Methodology

which

we

arc

said

to

search

for an

absolulc reality whose n a t u re

is

assumed

as

fixed i n d e p e n d e n t l y

of th el anguagechosen for itsdescr ipt ion .Thea n s w e r

to

aques t ionc o n c e r n i n g

reality

however

depends

n o t

on ly upon

that"reality"

or upon

th e

facts, but a lso upon the s t ructure (and the set

concepts)

of the

l a ng u a g e used for

the

descr ipt ion . In t rans la t ingone l a n gua ge i n t o a n o t he r

the

fac tua l

con ten t o f an empir ica l s ta tement c a n n o t a lways

be preserved

u n c h a n g e d .Such

c ha n ges

a rcinevitableifthe

s t ructures

o fthetw ol anguages

di f fe r

.inessential

po in t s . (1949, 125-126)

H e r e

we

havetw oof the key theses

oTthe^gostpositivisl

ph i losophyi

of science:, the

noncx i s t cnce

of ne u t r a l

facts

and

i n c o m m e n su r a b i l l y

in the foriTiof ' ' f tiftn^TrofiriKrrtTanshrtabHfly. NotcTttMrt-tucsc theses

were p ropou n ded i n the m id 1930s/for a l though I

have,

fo r thesake

ofconven ience ,quoted f rom the 1949 version o f

C a rnap ' s

paper , th e

re l evan t passageis

also

in

"W ahrhci l

u n d B e w a h r u n g "

(1936)./*

|

Given

these K u h n i a n themesor should wer a t h e r s ay Ca r n ap i an

th e me s? one

m i g ht predic t th a t Ca r n ap wou l d h av e f ou n dStruc ture

phi losophical ly congen i a l . That

this

w as

indeed the

case has been

d o c u m e n t e d b y

Rcisch

(1991).

St ruc tur e

was publ ished as par t of

the

I n t e r n a t i o n a l Encyc loped ia of Un i f i ed Science, of

which

Ca r nap w as

an

associateedi tor .A f t e r r ead ing the comple ted manusc r ip tfo r

Struc -

ture , Ca r nap wr o te to K u h n in A p r i lo f 1962.The text of

the

let ter

is reproduced in

Reisch

1991. I

will

quote f rom notes wr i t ten in

Carnap ' s a rchaics h o r th a n d .Carn ap beg ins wi th

a

piece

o fD a r w i n ia n

evolu t ion

an d

t hen adds,

c o n c e r n i n g

K u h n ' s

thesis,

In

a n a logy

to

this

one

has

to

un de r s t a n d t he de ve lopme n t

o f

scientific

the-

ories:

n ot

directed to an ideal[ true] theory, the

o n e

t rue theoryof the wo r ld ,

but

evolu t ion as a

step

to a

bel ter f o r m ,

by

selection

of

one

ou l of

several

compe t ing forms .The selection is

m a d e

on

ihc

basis of preference in

ihc

c o m m u n i t y

o f

scient is ts . M an y

factors,

sociological,

c u l t u r a l , . . . , a re involved.

Nol :

v

w e

a re a pp r oa c h in g i r u lh , bu t : we a rc i m p r o v i n gan instrument

An other im po r tan t though large ly tac it them e of S t ruc t u r e ,a

holist ic

view

of

m e a n i n g ,

c an

also

be

seen

as

emerging f rom

the

wr i t ings

of

the logical empir icists in the

1950s.

Hcmpe l , for example, took to

heart Quine 's at tack on the

analyt ic /synthet ic

d i s t i nc t ion ,which m ay

be taken to e m b o d y the thesis that there is asharp d is t inc t ion to b e

d r a w n be tween two f u nc t i on s o f

l anguage :

one to specify m e a n i n g ,

the other to make empir ica l asser t ions . Applying the mora l to sci-

ent i f ic

theories, one arr ives

a t

the conclus ion tha t there i s no p r inc i -

,*>


5/29

1 2

J o h n

E a r m a i i

pled

way to

d i s t inguish those postulates

of

th e

theory

tha t

m ay

proper ly

b e

d u b b e d m e a n i n g postulates.

It is

then

but a

seemingly

short

an d t e m p t i n g

step

to the

fur ther conclus ion tha t

all

the

pos-

tulatesof the

theory

function to specifythe mean ing of the constit-

u e n t

te rm s

a n d

thus tha t

an y

s ignif icant change

in

the theory

implies

a

change

in me an i ng .

This route

to

seman t ic hol ism cann ot

betraced to any of

Carnap 's

writings. Indeed, in his response to HempePs contr ibut ion to the

Schi lpp volume (1963), Carnap at tempted to use the not ion of the

Ramsey

sentence of the theory to

ident i fy

the postulates of the theory

tha t

"merely

represent

meaning relations"

(1963a,

965).

And in h is

last bo o k , Phi losophica l Foundat ions o f Physics

(1966), Carnap mai iv

ta ined th a t a sh a r p analyt ic-synthet ic dist inct ionis ofs u p r em e im-

portance for the phi losophy of science" (1966, 257). There

is,

however, another C arn apian route to sem an t ic hol ism, bu t tha t route

m u s t be

traced

all the w ay

back

to

Carnap ' s a t t e m p t

in the Aufbau

(1928) to expla in how scientific objectivity can

emerge

from a

recon-

struction

tha t

starts from

a

phcnom cna l i st ic

basis.

A n

explora t ion

of

this

m a t te r

w ou ld take

m e too far

afield;

I

willsim ply refer

the

reader

to Michael

F r i edman ' s (1987)

i l lumina t ing discussion.7

^ JV

/

3 Carnap's Relativism

losophy an d

Logical

S y n t a x " (1935)

proclainicd the

relat ivi ty

ol

a ll

philosophical

theses tol anguage .This

relativity

w as

supposed

tohold

the key to

so lv ing ,

or

rather dissolving, t rad i t ion al phi losophical dis-

putes .

Suppose,

for

example ,

on e

phi losopher

asserts,

" N u m b e rs

are -

primit iveentities,"

whi le

another proclaims, "Numbers are classes of

classes." They

m ay," C arn ap w ri tes, "philosophize w itho ut

en d

abou t

the

question

of

what numbers rea l ly are ,

but in

this

w ay

they

will

never

come

to an

agreement

(1935, 450).

If,

however, they

are

acute

en o ugh to

recognize Carnap's relativity principle, they

will

quickly

realize

that one is asser t ing, "In Language LI (Peano), numerical

expressions are elementary expressions," whi le the

other

ism a i n t a i n -

ing, "In

Language

L?

(Russell) numerical expressions

are

class

ex-

pressions of the secondorder.

"Now these

assertionsare

compat ible j


6/29

C a r n a p , K u l i n ,

an d

th e P h i l o s o p h y

o f Scienti f ic

M e t h o d o lo g y

wi th each o th e r an d bo th a rc t r u e ; the cont roversy has ceased to

exist"

(1935,451).T h is m o d e l for resolving phi losop hical dispu tes in

the

ph i losophy

of

m a t h em a t ic s

w as

supposed

by

C a r n a p

to be

cx tend-

iblc q u i te b road ly to phi losophical disputes, such as p h e nom e na l ism

versus

mater ia l ism an d the quest ion of whether space- t ime poin ts

have

an

ex i s tence i ndependen t

of

physical events .

Some, like Donald Davidson (1973), have found an air of paradox

in the

fact

tha t say ing i n one brea th (as Ca r nap th ou g h t he could)

tha t 5 is t rue in L \,

LS,

Las, . but false in L ? ,4, .. . seems to

presuppose

a

n e u t r al

m e ta f ra m e

wi thin

wh i chall thelanguage f rames

can

be

treated.

6

Others, l ike Michael Fr iedman (1992), have argued

t ha t

Carn ap ' s re la t iv ism is un de rcu t byGodel's incomple teness theo-

rems , wh ich show tha t

n o

such neu t r a l me ta f r ame

is

avai lable.

M y

objections are more localan d tactical.

Myfirstc o m p l a in tisth a t

Carnap

assumesw h a t

needs

to be proved .

Accord ing toCarn ap ' s "pr inc ip le of tolerance," we are free tochoose

whateve r

l a n g u a g esystem

w e

like.

T he

decision

islargelya

p r ag m a t ic

affair , t u r n i n gon such mat ters as efficiency an d

f ru i t fu lness

fo r the

-purposes a t h and . But to a p p l y the slogan o f "free

to

choose to

dissolve,

say,

the

p h e nome na l i sm v e r su s

m ater ial ism

deba te assumes

tha t a p h en om ena l i st ic langu age has been produ ced that shows how

physical object talk can be reduced to

talk

about sensa data or , as

C arn ap preferred, m om en tary total experiences ("Elementarer lcb-

nissc ).

This,

of course, is exactly what Carnap tr ied to do in the

Av/lau.

But by h is own admiss ion ,

th e

a t t em pt

has to coun ted as a

f a i lure

if, ash e o r ig ina l l y assumed , the

reduct ion

has to

proceed

v ia

explicit def in i t ions

an d

explicit Iranslalions. Similar ly,

to

a p p l y the

"free to choose slogan to dissolve disputes about the ontplogical

status

of space-t ime points assumes tha t i t can be shown how

space-

t ime poin ts can b econstructed out of events, such ascoincidences of

particles. Advocates

of

relat ional theories

of

space

an d

t ime repeat-

edly

claim that this can bedone an d even tha t i t has beendone. B ut

n o n e

o f

the c la ims s tands

up to

scrut iny.

7

I am

e mp h a t i c a l l y

n o t

c la iming tha t materia l ism

is

correct

or

that space-t ime points con-

strued as irreducible enti ties are essential to physics. Rather, I am

c la iming that the dissolution of the tradi t ional disputes on

these

matters is not as easy asCarnap made it seem.


7/29

M

John E a r m a n

A n o t h e r

c o m p l a i n t arises f rom

the b r ea t h t ak i ngscope of the in-

t ended appl ica t ion

of

Carnap's

di sso lving s tra tegy . A m on g

the

"phi lo-

sophical" disputes that C a r n a p proposed to treat in th i s way were

such

matters as

whether time

is finite or

inf ini te

an d

whether

the

world isdetermin is t ic .There isobvious lyavery s l ippery s lope here.

If the quest ionabout the fini lude of t ime is a philosop hical q uestion

in

the

re levantsense, then

why not the

q uest ion

of wh ether the

world

began from a b ig-bang s ingular i ty?An d if this latter question is a

phi losophicalqu est ion

in the

relevant sense, then

w h y n o t

otherdeep

ques t ions

in

cosmology?

B ut

more

impor tan t , one

does

n o t

have

to

go d o w n the slope to recognize the implausibihty of Carn ap 's pro-

cedure .E ven

i f one

agrees

to

talk

about

t ruth

in Lrather

than t ru th

period,

there is no plausibi l i ty to the idea that whether t ime is f in i te

an d whe ther determin ism holds a re mat ters to be settled in L by

adopt i ng l inguis t ic rules for

L

rather than by consul t ing the facts .

C a r n a p ,

n o t

surpr i s ingly , acknowledged

the

po in t . Speaking

of the

determin ism

issue, he said,

Theob jection m aypcriiaps be raised at this point that the form of physical

laws

d ep end s upon exper imenta l resu l ts

of

physicalinves t iga tion ,

an d

tha t

it

is not d e t e rm i ned by a merely theoretical syntactical

consideration.' This

assertion isqu i te r ight , b ut we

m u s t bear

in m i n d the fact

tha t

the empir ical

results

at which physicis ts arr ive by way of their laboratory exper imen t sby

no means

d ictate

theirchoice

between

th e

determinis t ic

an d the statistical'fo rm

of

laws.

The

fo rm

in

w h i c h

a law is

to be slated

has

tobedecided

by an act

of

voli t ion.

Thisdecision, it ist rue ,

d ep end s

u p o n the empir ical resul ts , but

n ot

logically,

on ly

pract ica l ly .

The

results of

the exper iments show

merely

i l l . i l

on e

mode

of fo rmu la t ion wou ld be

m o r e

sui table t h a n ano the r . (1935,

455)

These s en t imen t s

resonate with those Carnap expressed three de-

cades la ter in comment ing on

K u h n ' s St ruc ture .

B ut here the senti-

ment s

arc not to the point. T he issuei s not

whether ,

for D u h e m i a n

or

o ther reasons,

the resultso f

exper iments ,

say the

recen t E ins te in ,

Rosen, Podolsky, and

Bell

type of exper iments ,

fail

to dictate the

acceptance o f

i nde te rmin i s t ic

laws. Rather the issue is whether deter-

min i sm is a scientif ic claim to be argued over the way one argues

over otherdeepscien t i f ic c laims, n on e

of

w hich ever gets

definit ively

settled by the dictates of experimental evidence; o rw hether

deter-

min ism is a

c la im that

can be

made t rue

by

l i ngu i s t i c

fiat in

L\

Lr , ,


8/29

Ca rn a p , K u h n , an d the Philosophy

of

Scientific

Methodology

35, . . . and false by l inguis t ic fiat in L

2

, LT , 37 . . .. . an d then w e

j u s t

p a ysour m o n e yan d takeso ur choiceo f language . Aga inI

re fuse

to give a global

a n s w er

to th i s que ry an d favor instead a

tactical

response.All in dica t ion s are tha t the debate over theimp l ica tions for

deter i j i in ism of the

Bell

inequa l i t ies and the

Aspect exper iments

be longs

to

the f o r m e r r a t h e r than to the la t te r . Indeed , ind ica t ions

are

t h a t

i n any l anguage

sys tem adequate

for the

f o r m u l a t i o n

o f

theoriestha tsavethe exper imenta l lyverifiable q ua n tum s ta ti stics ,the

laws m u s t

b e

inde termini s t i c .

9

I

suspect

t h a t

Carnap ' s

relativism

began

b y hisbe i n g

impressed

b y

th e ach ievements o f Frege, Russell, an d others in the ph i losophy of

mathema t i c s

and was fu r the red by a misplaced zeal for extend ing his

m o d e l for resolving

ph i lo soph ica l d i spu te s

in this area

to

a

broad

area of ph i losophica lan d scient if ic questions. O f course, wha teve r

the origins of Carnap's relat ivism, it or

s om e th i n g

like it could per-

hapsb e promoted on the basis of his doct r ine tha t language-neut ra l

facts do not exist. I find it di f f icul t to assess this matter, since I do

not f ind in Carnap ' s wr i t i nga he lpfu l explana t ion o f

this

In

th e fol lowing section

I will

c o m m e n t

on the related

doc t r i ne

o f

Feyc ra bc n d ,

H a n s on ,

an d

Kuhn tha t observa t ion

is

theory laden .

In closing this section, Inote tha t Carn ap displayed a con sistency

on th e

ma t t e r

at

h a n d

n o t

the

consistency that

is the

hobgoblin

of

l i t t le m i n d s but the magn i f i c en t consistency of a grand v is ionary . In

his

c o n t r i bu t i o n t o

the

Sch i lpp vo lume fo r Carnap ,

H e r b e r t Fcigl

(1963) ske tched a mind-body ident i ty

theory

that he was later to

elaborate

in his

f a m o u s

essay

The

'M e n t a l ' an d

t h e T h ys i -

caF"(1958). ' Clearly, the politically

correct th ing for Carnap was to

endorse Fcigl 'sapproach. Ins tead , he wrote , "it seems preferable to

m e to formula te the ques t ion [of mind-body ident i ty] in the meta-

lan guag e, not as a

factual

ques t ion abou t the w or ld ,but as aques t ion

conce rn ing the choice of language . Al though w eprefer a d i f f e r e n t

language , we m us t adm it tha t a dua l is t ic

l anguage

can be con structed

an d

used

w i thou t coming in to con f li c t

with

cither

the

laws

of

logic

or

with

empi r i c a l l y known

facts"

(1963b,885-886).

4 Kuhn's Re lativism

K u h n resists being labeled a relativist. I use

the

labelhere tore fe r to

three doct r ines o f Struc ture: the theory ladenncss of observat ion , th e


9/29

]G

John

Earnian

n c o m n i c n s u r a b i l i t y

o f

theories,

an d (l ie d e n i a l t ha t

there

is a

l l i co ry -

indcpcndcnl

notion

of

truth.

Pa r t of w h a t w as

meant

by the

theory ladcnncss

o f observation is

embodied in the

thesis that

what we see depends

upon

what we

believe,athesis

open

tochallenge

(see

Fodor 1984). I am

concerned

rather with

therelated

thesis

of the nonexistence of aneutral

obser-

vat ion language

in w h i c h

different theories

can be

compared.

M y

response is once again tactical.

That

is, without trying to adjudicate

thegeneral merits of the

thesis,

I claim that things

aren't

so bad for

actual

historical

examples.

Even

for

cases

o f

major

scientif ic

revolu-

t ions, we

cari

find,

without having

to go too far

downward toward

some t h ing like foundations for knowledge, an observation basethat

is neu t ra l enough

fo r

pu rpos e s

a t

hand. A

nice

e x a m p l e is

provided

by

Allan Franklin

(1986,

110-113), who shows how to construct an

experiment that

is

theory-neutral enough between Newtonian

and

special-relativistic

mechanics to unambiguously

decide

between the

predictions

of

these

theories for elastic

collisions.

The two

theories

agree on the procedure for measuring the angle between the

velocity

vectorsof thescattered particles,and the two

theories predict

differ-

~

en t

angles.

A b

More

generally,

I

claim that

in the

physical sciences there

is in

pr inc iple

always available

a

neutral observation base

in

spatial coin-

cidences,such asdots on photographic plates, pointer positions on

dials,

and the like. If intcrsubjective agreement on such

matters

were

n ot

routine, then physical science

as we

k n o w

it

would

no t b e

possible.

1 reject, of course, the posilivistic attempt to reduce

p'hysics

tosuch

coincidences.

A n d I readily acknowledge that such coincidences b y

themselves

are

mute

witnesses in the

tribunal

forjudging theories.

B ut

w h a tis required to make these mute witnesses articulate is not a

Gcstaltexperiencebut a

constellation

of techniques,hypotheses,and

theories: techniquesof

data

analysis, hypotheses aboutthe operation

of measuring instruments,

and

auxiliarytheories thatsupportboot-

strap calculations of values for the relevant theoretical

parameters

t ha ttestthecompeting theories.But Iagain assert thatto the

extent

tha t

this process cannot be explicit ly articulated but relies on some

su igeneris

form

of perception,the

practice

is not

science. This

is not

tosay, however, thatthevulgar imageofscienceas ab l i nd lyimpartial

enterprise

is correct, for the articulation uncovers assumptions to


10/29

17

Carnap, K u l i n ,

a nd the

Phi losophy

o f

Scient i f ic Method o log y

which d i f f e r e n t

scientists may assign vc fy

different , degrees

of con-

f idence .

B u t

this

sense

in

which

di f ferent scient is ts can

(mis lcad ing ly )

be said to see di f f e ren t th ings when looking a t the same phenom -

enon

is one with which a

probabil istic

or

Bayesian

epistemology the

k i n d

of

epis temology w hich

the

la ter Carn ap came to

advoca tem ust

cope on a routine basis ,

even

incases fa r away f rom the boundar ies

of

scient if ic

revolut ions .

H ow

these di f ferences

are resolved is

pa r t

of

the

Bayes ian ana logue

of

K u h n ' s problem

of

com m un i ty dec is ion

on

theo ry choice. Kuhn 's problem

will

b e

encoun te red

in

the

follow-

in g section, an d the Bayesiananalogue will be discussed in sections

8 and 9.

T he m a t te r o f incom m ensu rab i l i ty i s m uch more diff icult to discuss

for tw o reasons.

First ,

it is tied to di f f icul t is sues about me an in gan d

reference tha t

I

cannot broach

here.

Second, issues about incom-

mensurab i l i t y

present amorphous and shi f t ing targets. In Struc ture ,

for

example , i ncommensurab i l i t y

was a

label

for the

entire constel-

lation

o f

factors that lead proponents

of

d i f f e ren t pa rad igms

to

talk

past on e another . In recen t years Kuhn has come a round to a

more

Carnap ian

or

l inguis t ic fo rmula t ion

in

which i ncommensurab i l i t y

is

equated

wi th

un t rans l a tab i l i t y . More

specifically, the

focus

has

shif ted

from paradigms to theories, and two theories are said

to

b ei n c o m -

mensurab le just in case

there

is no common language in to which

both can be fully translated ( K u h n1989, 10). I have no doubts about

K uh n ' s cl aims tha t

theories

o n d i f f e r en t

sides

o f ascientificrevolut ion

often

use

di f ferent " lexicons," that di f ferences

in

lexicons

can

m a k e

fo r a

k i n d

o f

un t r a n s l a t a b i l i t y ,

an d

tha t

in

t u r n this

exp la in s w hy

scientists r e ad i ng out-of-date texts of ten

e n c o u n t e r

passages tha t

make

no

sense

(1989,9). But I deny

thatthere

is

i n comm e nsu ra -

bi l i ty /untransla tabi l i ty

tha t makes

for

insuperable difficulties

for

con-

firmation or

theory choice

(a

phrase

I

don't l ike

for

reasons

to be

given below)

in the

s tandardly c i ted cases

of

scientific revolut ions

such as the t ran si t ion f rom N ew ton ian to special- rela t ivis tic m echan ics

an d

the

su bse qu e n t transi t ion togeneral rela tivi ty . N ew ton ian , spe-

cial-relativistic,

gcncral-relativistic, and

m a n y

other theoriescan all

be

f o rm u l a t ed

in a

common language,

the

language

of d i f fe ren t ia l

geometry

on a

four -d imen s iona l m an i fo ld ,

and the

cruciald i f ferences

in the

theories

l ie in the

dif ferences

in the

geometric object

fields


11/29

J8

John E a r m a n

postulated

an d the m a n n e r i n wh i c hthesef ieldsrelateto such

t h i ng s

as

particle orbits .

This

language is

an achron is t ic

and so may not be

th e best device

to

use when t r y i n g

to decide

various historical dis-

putes. But i t

does

seem to me to be an

app r op r i a t e vehicle

for

f r a m i n g an d an swe r i ng the sorts of quest ions of most concern to

w or k ing

physicis ts

an d philosophersof

science.

For

example,

on the

basis of the

avai lable

evidence, what is i t reasonable tob elieve about

the

s t ruc ture

o fspace an d t ime and the n a tu re o f gravi ta t ion?This

is not to saytha t the common language makes for an easy answ er. It

is

indeed a

d i f f icul t

business, but i t is a business that

involves

the

same sorts o f difficult ies a l ready

present

w h en test ing theories t ha t

lie on the same side of a scient i f ic revolut ion. Finally, so that there

can be n o m i s un de r s t a n d i n g ,

let

m e repeat: I am not c l ai m i n g ( h a t

w h a t

I

call

a

common l anguage prov ides wha t K u h n wan t s . It docs

n o t

show,

fo r

example , tha t

the

N e w t o n i a n

and the

E i n s t c i n i a n

can

b e

b rought i n to agreemen t about wha t

is and is not a

"m ea n i n g f u l "

quest ion

a b o u t

s im ul tane i ty .

But w ha t I do cla im is that

these

res idua l

e lement s

of i n c om m en s u r a b i li ty

d o no tu n d e r m i n es t anda rd accoun t s

of

theory test ing

an d

con f i rma t ion .

1 2

My response

to

worries

about the

appl icabi l i ty

of the

no t ion

of

t r u t h

tow hole theories iss im ilarly localan d

tactical.

In the Postscript

to the second edition

o f S t ru c tu re ,

Kuhn wr i t es ,

There

i s , I th in k , no

t h e o ry - i nd e p e n d e n t way to

recons t ruc t

phrases like 'reallythere'; the

not ion

of a

ma tch between

the

ontology

of a

theory

and its

' rea l '

c o u n t e r p a r t

in

n a t u r e

n ow

seems

to me

illusive

in pr inc ip le"

(1970,

206). I need n o t

d e m u r

if " theory" is

unders tood

in 'a very broad

sense to mean something l ike a conceptua l f r a m e w o r k som i n i m a l

tha t w i tho u tit "the world" would b e un d i f f e r en l i a t ed Ka n t i a nooze.

B ut

I do

d e m u r

if

theory

is

taken

in the

ordinary sense,

i.e., as

Newton ' s theory o r special - rela t ivi ty theory o r genera l - re la t iv i tythe-

ory.

13

For scient is ts are current ly working in a f rame in which they

can

say, correctly

I

t h i n k ,

tha t

the

match between

the

ontology

of

the

theory and i ts real counterpar t in n a t u r e is

better

for th e special

theory

o f

relativity

an d evenbetter for the

gen era l theory.

O f

course,

to get tothis position required tw om a jor coneptua l revolut ions . H ow

such revolutions affect theory choice, or as I would prefer to say,

theory testing an d con f i rma t ion , rema ins to be discussed.


12/29

]9

C a r n a p , K u h n ,an d the Ph i losophyo fScientif ic Methodology

5

Kuhn's

Accountof

Scientific Revolutions

Carnap,

as wehave

seen,

found

Kuhn's

Structure

congenial.

But

m a n y

philosophers

of the younger

generation,includingthose

who

prided

themselves on having

gone

beyondthe crudities of

logicalpositivism,

professed

shock and

dismay

at

Kuhn'saccount

of the

displacement

of

an old

paradigm

by a new

one.

For

those

readerswho do not

have

a copyofStructure to

hand,

hereare someof the

purplepassages:

Like

th e choice between competing poli t ical ins t i tut ions , that

between

com-

pet ing

parad igms

proves to

be a

choice

between

incompat ib le

modes

of

c o m m u n i t y

life.

.

..W h e n

parad igmsen ter, as

they

m us t , in toa deba te abou t

parad igm

choice, the i r role is

necessarily circular.

Each group

uses'

i ts own

parad igm to a rgue in t h a t p a r a d i g m ' s

de fense .

(P. 94)

As

in poli t ica l revolut ions , so in parad igm choicethere i s no s tandard

h ighe r t h a n th eassentof

the

re l evan t

c o m m u n i t y .

To discover how

scientific

revolu t ions arc

effected,

we

shall

therefore

have

to

e x a m i n e n o t on ly the

impact o f n a t u r e and logic, but also the t echn iques of pe rsuas ive a rg um en -

tation

w i th i n

th e

c jui lc

special

groups

tha t

cons t i tu te

th e

c o m m u n i t y

of

sci-

entis ts . (P. 94)

The

p r o p o n e n t s

of compet ing parad igms prac t ice the i r

trades

in d i f fe ren t

worlds. . . . Prac t ic ing in d i f ferent wor lds , the tw ogroups of scientists sec

d i f f e r en t t h i n g s w h e n they look from the same point in the

same

direct ion.

(P. 150)

In thesema t t e r sn e i t h e rproof n orerror is atissue.The

t r an s fe r

ofallegiance

from

pa r ad igm

to

parad igm

is a

con version

exper ience

tha t

c a n n o t

be

forced.

(P .151)

Before they can hope to c o m m u n i c a t e fully, on e group or the o ther mus t

exper ience th e

conversion

tha t we have been cal l ing a paradigm shif t . Jus t

because it is a

sh i f t between

incommensu rab les , the t rans i t ion

between

com-

pet ing

pa r ad igms

c a n n o t

be

m a d e

a

step

at a

time, forced

by

logic

an d

neu t r a l experience. Like a gcslalt switch, it must occur all at once

( though

n o t

necessarily at an

i n s t an t )

or not at al l . (P . 150)

M a n y

readers

saw in

these

passages

an

open

i n v i t a t i o n

to aralio-

na l i t y if not outright irrationality.Thus Imre

Lakatos

took

K u h n

to

besaying that theory choice is a matter of "mob psychology

(1970,

178), while DudleyShapcreread Kuhn assayingthatthe decision to

adopta newparadigm

cannot

bebased ongood reasons (1966, 67).


13/29

20

John

E a r man

K u l i n

inturn w asequ a l lyshocked b ysuch criticisms.In thePostscript

to thesecond edi t ion o f St ruc ture (1970),he professed

surprise

that

readers could have imposed such unintended interpretationson th e

above quoted passages.

I

will leave aside

the

u n f r u i t f u l question

of

w h e t h e ror not

K u h n

ought tohave

anticipated

such interpretations

an d

will concentrate instead on what, upon reflection, he i n t e nd e d

to

say.

K u h n ' s

ow n exp lana t ion in the

Postscript begins

wi th the

common-

place tha t debate over theory-choicecannot be cast in a form tha t

resembles

logical

o r

mathemat ica l

choice

(1970,

195).

B ut

he

has tens

to

add

that this commonplace

doesnot

imply that there

are no

good

reasons for

being

persuaded or that

these

reasonsare not

u l t im ate ly

decisive

for the group (1970, 195). T he reasons listed in the Post-

sc r ip t

areaccuracy,s implic i ty ,and f ru i t fu lness . The later paper Ob-

jectivi ty, Value Judgments,

and

Theory Choice (1977)

added two

f u r t h e r reasons:consistencyand scope.And asKuhn himselfnotes,

the final

list

does

not

d i f fer

(with

one

notable exception

to be

dis-

cussed later) from similar lists drawn from standard phi losophy-of-

scicnce texts (see also Kuhn 1983).

These soothing sentiments serve todeflate charges ofarationality

and

irrationality, but at the same time they also serve to raise the

ques t ion of how Kuhn's viewsare to be distinguished from the or-

thodoxy

that Structurewassupposed to upset.The answer givenin

the

Postscript contains

tw o

themes, which

are elaborated in Objec-

tivity."

First,

the

items

on

the

above

list

a re

said

to

function

as

values"

tha t can be

d i f f e ren t l y app l i ed ,

i n d iv idua l ly an d

collectively

b ym en

whoconcurinhonoringthem (1970, 199).Thus, thereis noneutral

algor i thmfor

theory choice,

no

systematic decision procedure which ,

properly applied, must lead each individualin thegroupto the s ame

decision.

Second, it

(supposedly) follows that

"it is the

c o m m u n i t y

of

specialists

rather than the individual members that makes the

effective

decision (1970,

200).

I

th ink

that Kuhniscorrectinlocating objectivityin thecommunity

of

sp ecialists,

atleastin the uncontroversialsensethat intersubjective

agreement among the relevant experts is a necessary condition for

objectivity. But how the communityof

experts

reaches a decision

when the individual members d i f fer on the application o f shared

values is a mys te ry that to m y mind is not

adequa te ly

resolved b y


14/29

21

C a r n a p , K u h n ,

an d ihc Phi losophy o f

Scicnlific Mclhodology

Struc ture or by s u b s e q u e n t wr i t ings . M ystrategy will be to

explore

these

an d related

issues from

the

perspective

o f

Carnap's

cpis tcmology.

6

Carnap

and

Kuhn Incommensurability?

The passage Reisch

(1991)

quotes from Carnap's letter toKuhnand

the passage from Carnap's shorthand notes I quoted in section 2

would seem to ind ica te

that Carnap

an d

K u h n were

in

subs tan t ia l

a g r e e m e n t

as

regards

paradigm

choice.

This

is

surely

the

case

w h e n

paradigm is

interpreted

to

m e a n

something l ikea l inguis t icframe-

w o r k . A t this

level

Carnap wouldagree, indeed, would insist , on th e

need tochoose, and hewould hold t h a t thechoice

is'a p r a g m a t i c

on e

whosedynamicsm ay well invo lve the

sorts

of factors emphas i zed in

K u h n ' s account. B ut w h e n

the

focus shifts to theories, as itdoes in

K u h n ' s later writings,

the

disagreement begins.

In the f i rs t

place,

K u h n ' s list

ofcriteria fortheory choice isconspicuousfor itsomission

of any

reference

to the

degrees

of

confirmation

or

probabilities

of

the

theories.

This is not an

oversight,

of

course,

but

derives both

from explicit doctrines, suchas thenonexistence of atheory-neutral

observation language, and the largely tacitbut pervasive anti-induc-

tivism

of

S t ruc t u re . Needless

to

say, this shunning

of

confirmation

theory

is

most u n - C a r n a p i a n .

B ut

even more anomalous from Car-

nap's

perspective

isKuhn's emphasisontheory choiceor

acceptance,

for in Carnap's version of epistemology,

theories

arc not chosen or

accepted

b u t

o n l y

p robab i I i f i ed .

M

Carnap's

writingsinthe1940sand

1950s

portrayhim as espousing

a logical

conception of

probability.

But by the

late 1950s

an d ear ly

1960s,

he

clearly favored

a view

that

can be t e rmed

tempered per-

sonal i sm: probability

is

rational degree

of

belief.

15

I

will

h a v e

more

to say on

this matter

insection 8, but in the

m e a n t i m e

I

will present

Carnap

as a

tempered Bayesian personalist.

A

shotgun marriage

of

Kuhn

and

Carnap

could

be

arranged

by

t ak ingCarnap

to

supply

the

probabilities,

K u h n to

supply

the

values

or

utilit ies,

and

then applying

the

rule

of

maximizing

the

expected

utilityto

render

adecisionon

theory choice.

16

But

likemost shotgun

marriages, this

one

would

be a

mistake.

For

Carnap

it

would

be a

mis take because it w o u l d

invo lve the

pretense t ha t

the

accepted

the-


15/29

22

John Carman

ory

is certa in even t h o u g h

one's

degree of belief in

the

theory may

be less thanone,perhaps substant ia l lyso. For K u h n it would alsobe

a mis take,

since

the

efficacy

of his values

does

n ot

depend

on the

t ru th

o f the

theories,

so

estimates

of the

probable t ruth

of the

theories

is

i r relevant

to K u h n i a n

theory choice.

Part

of the

wrang le here derives from

the

un f o r t un a t e ph ra s e

"theory choice." Scientists do choose theories, but on beha l f o f Car-

n a p , Iwould c l aim th a t they

choose

themon ly inthei n n o c uo ussense

that theychoose to devote their t ime an d energy tothem: toart icu-

la t ing

them,

to

i m p r o v i n g th e m ,

to

drawing

ou t

their consequen ces,

to

confront ing

them

withthe results ofobservationand experiment.

Choice in thissense allows for a reconciliation of

Bayes

a n d K u h n ,

since

thischoice

is i n fo rm ed bybo th Baycsian an d Kuhnian fac tors :

probabil i ty an d

th e

valu es of accuracy, consistency,scope, simplicity,

an d

f ru i t fu lncss .

Alas, this reconcil iation israther shallow. Once we are clear tha t

th e sort of choice involved in

" theory

choice" is a p ractical

one, there

is

n o t h i n g

sacred

a b o u t

the

list

of

i tems

on

K u h n ' s

list

of values.

Other

values,

such as

ge t t i ng

an

N S F

g r a n t or w i n n i n g the

No be l

Prize,

can and do

enter.F u r the r,

the

k ind

of

choice

in

quest ion a l lows

a

scientist to be bigamous, s ince he can choose to work on two or

more theories at

once,

and i t al lows him to be fickle, since he can

oscillate back and forth. The kind of choice Struc tureenvis ioned w as

m u c h more p e r m a n e n t ; indeed,

the

impression given there

is tha t

norma l

science

is not

possible

without tying Cathol ic

bonds

to a

theory,b o n d s

tha t

can o n l ybe broken b yl eav ingthe C h u r c h , i.e., by

creat ing a revo lu t ion .

Is there no way to b r idge the gap be tween Carnap an d K u h non

this

issue? T o see howba f f l ing the Bay esian f inds the not ion of theory

acceptance, con sider the case of Einstein 's gen eral theory of relativity

( G TR ) ,

a rguab ly the leading theory o f gravitation an d thus the top

candidate for acceptance. Marie, a research worker in the field fa-

miliar

with

all

of the

re levan t exper imenta l

f indings ,

does

some

in -

trospection and finds

that

her degreeof belief in GTR isp.

Case

1: p is1 or so

n e a r

1 a s makes no

odds . Here

there

is a n a t u r a l

sense in which the Bayesian can say that Marie accepts GTR. Such

cases,however,arc so

rare

as to const i tute anomalies .Ofcourse,one


16/29

23

C a r n a p ,

K u h n ,

an d

llic Phi losophy

of

Scientif ic Mclhodology

can cite any number of cases f rom the his tory of

science

w h e r e

scientistsseem

to besayingfor

their

pet

theories

that theysetp= 1.

Here

I

would

urge

the need

to dis t ing uish

careful ly

between

scien tists

as advocates

of

theories versus scientists

asjudges of

theories.

T he

latter

roleconcern sushere,and in

that

role

scientists

know,or should

k n o w ,

tha ton ly in v ery exceptiona l

cases

does the evidence rat ion al ly

suppor t a

full

belief in a theory. Let us move on to case 2.

Case

2: p is , say , .75. Subsequent ly Marie decides to

accept

G T R o n

the

basis

of her

probabil i ty

assignments and the

values

she attaches

to GTR and its

competitors.

W h at

could

th i s mean?

Subcase 2a .

W h e n

she

accepts GTR, Marie changes

her degree of

belief from .75 to 1.

This

i s no th ing

short

of

folly, s ince

she has

a l ready

m a d e

a considered judgment about evident ial

support

an d

no new

relev an t evidence occasioning

a

r e j u d g m e n t

has

come

in .

Suitcase 2b . W h e n

she

accepts

G T R ,

Mar ie

docs

n ot

c h a n g e

her de-

gree of

belief f rom

.75 to 1 , bu t she

acts a sz / a l l doub t were

swep t

away

in

t ha t

she

devotes eve ry w ak in g hour

to

show ing tha t var ious

p u z z l i n g

as t ronomica l

observations

can be exp la ined by the

theory ,

she

assigns her graduate s tudents research projects that presuppose

the correctness of the theory, she wri tes a textbook ongrav i ta t ion al

research

that

isdevoted

almost exclusively

to

GTR, etc.

But at this

p o i n t

w e

have come

full

circle back

to a

sense

of

theory acceptance

t h a t

is

really

a

m i s n o m e r ,

for

w h a t

isinvolved is a

practicaldecision

about the allocation of

personal

and insti tutional resources and not

a decis ion about the

cpis tcmic sta tus

of the theory.

This ra ther pedant ic d ia t r ibe on theory acceptance would b e best

forgotten were

it not for

its impl icat ions

for our

p ic ture

o f

n o r m a l

science. Aswe have seen, theory

choice

or "acceptance" can refer

cither to adopting an epislemic

attitude

or to mak ing a practical

choice. In the form er case there is n o n atu ra l Bay esian explication

of theory acceptance save in the case where the probabi l i ty of the

theory isone.

Since scientists

asjudgesoftheoriesare

almost never

in

a

position

to

ju s t i fy

such

an

acceptance,

th e

Bayesian predict ion

i s

t h a t rarely is a theo ryaccepted in the epis temicsense.S imilarly,w h e n

theory choice is a

m a t te r

ofdeciding w hat theory todevote

one'sl im e

an d energy to, the Bayesian predict ion is tha t in typical s i tuat ions


17/29

John

l .arnian

where members of the c o m m un i t y a s s i gn d i f f e r en t

utilities

to such

devotions,

they

will

m a k e

di f ferent choices .

Thus

from

e i ther

the

cpistcmic

or

practical-decision

perspective,

the

Bay esian

predic t ion

is

diversity.

This

predict ion

is, I

t h i n k ,borne

out by

actual

scientific

practice.

In

section

9below

Iwilla rgue that insofar

as

normal science

implies

a

shared pa rad igm,

the

pa rad igm need

not and in fact

of ten

is

not so

specific

as to i nc lude a pa r t i cu l a r

( accepted ) theory .

I

w i l l

also

hazard a

proposal

for a

m i n i m a lsense

of

"shared p a r a d i g m "

tha t

yields

a less

strai t- jacketed image

of

n o r m a l

science an d

that also

d imin i shes

wi thout ob l i t e ra t i ng

the

di f ference between normal

an d

revolut ionary

science.

By way o f closing this section an d

i n t r od u c i ng

the

nex t ,

I

will

cons ider a f inal way of reconci l ing K u h n an d C a r n a p on theory

choice. Radically n ew theories, so the story goes, carry with them

di f fe ren t l inguis t ic /conceptua l f rameworks . Thus,

even

seriously

lo

enter ta in the new theory involves the decision to

adopt,

if on ly t en -

tatively,

the new framework, and this decis ion is for Carnap a

prag-

matic on e that involves the sorts of factors emphasized i n K u h n ' s

account o f paradigm

replacement.

In

response

I would

repeat

w h a t

I have

a l ready

said insection 4: major scientific revolut ions

such

as

the

t rans i t i on f rom Newton ian to special-relativistic physics- an d

thence lo genera l rela t ivi tyneedn't be seen as forc ing a choice be-

tween i n c o m m e n s u r ab l el ing uist ic /con ceptualsystems, since

it is of ten

possible lo f i t

ihc possibilities in to

a

la rger scheme tha i m a kes

llic

theories c o m m e n s u r a b l e lo the

ex ten l

lhal

conf i rmal ion

ques t ions

can

be

posed

in t e rm sof an observat ion

base lhal

isn c u i r a l e n o u g h

for assessingihe

re la l ive conf i rmat ion

of

the

theories.

However,

ihe

rccognil ion of ihe

larger

possibil i tyset canproduce adrastic

c h a n g e

in prob abi l i ty va lues , achan ge best

described

in K u h n i a n

terms.

7 Revolutions andB elief Shifts

A mild

f orm of scient i f ic revo lut ion occurs w ithihe in l roducl ion of

a new

llieory lhal articulates possibil i t ies

thai lie

wi lh inihe b o u n d -

aries of

ihe

space of iheories to be taken seriously b ut that , because

of the fai lure of actual scientists to be logicallyom nisc ien l , had pre-

viously been unrecognized as explicil possibilities.T he more radical

form

of revolulion occursw h e n ihe spaceof possibilities itself needs


18/29

25

C a r n a p , K u h n , an d

ihc

Ph i losophy

o f Scicnl i f ic

Methodology

to be s ign i f ican t ly al tered to encompass

the

n ew theory . In practice

the

d is t inc t ion

between

the two forms of revolu t ion may

be b lu r r ed ,

perhaps even hopelessly so, but I w i l l begind iscussion by

p r e te n d i n g

t ha t

we can per form a

separat ion

ofcases.

Even the mi ld form of revolu t ion may induce a non-Bayes ian shi f t

in belief func t i ons . By non-Bayes i an I

m e a n

that no form of condi-

t iona l i za l ion , whether s t r ic t o rJeff rey or some natura l ex tens ion o f

these, w i l l suffice to expla in

the

ch ang e . For cond i t iona l i z i ng ( in any

recognizable sense of

the t e r m ) on the i n fo rm at ion tha t j u s t n o w a

here tofore una r l i cu l a ted

theory

T

has

been

i n t roduced

is

l i terally

nonsens ica l ,

becausesuch acon di t ion al iza t ion

presupposes

that pr ior

to this t ime there was a w el l-defined probab i l ity for th i s i n for m at ion

an d t h u sfo r T , wh ichisexactly wh at th efai lureof logical om niscience

rules

out.

W e can t ry to acknowledge the

f a i l u re

of

logical

omnisc ience b y

m e a n sof A b n e r

Sh i m on y ' s

(1970) deviceof acatch-all hy poth esis

H

f

,

which

asserts in e f fec t tha t someth ing , we know not what , beyond

th e

previously formulated theories

T\

T z,

. . . ,

T

T

is

t rue.

Now

suppose tha t a new theory T is introduced an d tha t as a result the

old degrce-of-bcl ief f u n c t i o n Pr ischanged to Pr ' . T he most conser-

vative

way the

sh if t f rom

Pr to

Pr' could take

place

is by the

process

I will

call

sha ving

o f f , n a m e l y ,Pr(T,)

= .P r ' ( T i ) for i = 1, 2, . . . ,qan d

Pr'(T) = r > 0 and

Pr'(//

e

)

= Pr(//

c

)- r.Thatis,u n d e r shav in g o f f ,

H

f

serves

as a well

for init ial

probabilities for as y et u n b o r n

theories,

an d the

ac tua l

i n t roduc t ion of new

theories resul ts only

in

d r a w i n g

u p o n

this

well w i t hou t d i s t u r b i n g th e probabi l i t ies o f

previously

for-

mu la ted theories . U n fo r tun a te l y , such conse rva ti sm even tua l ly leads

to the a s s i g n m e n t of ever smal ler

in i t ia l

probabi l i t ies to successive

waves

of n ew

theories

u n t i l a

p o i n t

isreached

where

the new

theory

has

such

a low

ini t ial probab i l i ty

as to

s tand

n ot

m u c h

of a fighting

chance .

Cer t a in ly s h a v i n g

off is a factual ly

inadequate descr ip t ion

of

w h a t

h a p p e n s

in

m an y scient i f ic revolut ions , especial ly

of the

more radical

type . Th ink o f w h a t happened fo l l owing the in t roduct ion of E i n -

stein's special theory

of

relativi ty (STR)

in

1905. Between 1905

an d

1915 little n ewempir ical evidence in favor o f S T R wa srecorded, an d

yet th e probabi l i ty of compet ing theories, such asthose of Lorentz

an d A b r a h a m , set in classical

space

an d t ime,

fell

in the estimates of


19/29

26

John Ea r m a n

most

o f

th e m e m b e r s

of the

E u r o p ea n p h ys ic s c o m m u n i ty ,

and the

probab i l i t y

subtracted

from

these

e lect ron theor ies

w as

t rans fe r red

to E ins te in ' sSTR.The probabi l i t iesof au xi l ia ry hypothesesmayalso

be a f fec ted , as i l lustrated by the in t roduc t ion of the general theory

of relat ivity

(GTR).

When Eins te in showed tha t

GTR

accounted

for

the exac t am ou n tof the anomalous advance ofM ercury ' s pe r ihe l ion ,

the

hypothesis of an amount of zodiacal

matter suf f ic ien t

to

affect

Merc u ry ' s per ihel ion dropped dramat ica l ly in the estimates of mos t

of the

phys ics communi ty ( see Earman

and

Glymour 1991) .

In u s i n g

the

term non-Bayesian

to describe

such noncond i t ion -

alization bel ief chan ges , w hether of the conservative shaving-off type

or

some more rad ica l fo rm,

I do not

mean

to

imp ly tha t

the

changes

are not i n f o r m e d b y

Bayesian

considerat ions . Indeed, the problem

of the t rans i t ion f rom Pr to Pr' can be t hough t of as no more and

no less than the fami l i a r Bayesian problem of ass ign ing ini tial

prob-

abili ties, on ly n ow

wi th

a new in i t ia l

si tuat ion

i nvo lv ing a newset of

possibilities

and a

n ew

in fo rm at io n bas is . B ut the

problem

we

arc

n ow f ac ing isq u i t eu n l i k ethose a lleged ly solved b yclassical pr in cip les

of

ind i f fe rence

or

modern var ian t s the reof , such

as E. T.

Jayncs 's

m a x i m u m - e n t r o p y

p r inc ip le , where

it is

assumed

w e

k n o w n o t h in g

o r

very

little ab ou t the

possibilities

in

question.

In

typical

cases the

scientific

c o m m u n i ty willpossessa vas tstoreo f relevan t exper im en ta l

an d

theore t ica l in format ion . Us ing tha t in format ion

to

i n f o r m

the

red is t r ibu t ion

of

probabil i t ies over

the

competing

theories

on the

occasion

of

thei n t r o d u c t i o n o f

th e

new theory ortheories is a

process

t ha t , in the str ict

sense

o f the t e r m ,

is\o?Slipnal:

i t cannot 'be accom-

plished

by some nea t fo rm al ru les o r ,

T o

u s e K u h n ' s

term,_bvan

a lgor i thm.

On the

otherjjand,

the

process

is far f rom

beirgjrrationa>>

since it is informecf by reasons. But the

reasons,

as

K u h n

Tias~crrf-

phasized, come in

the

f o rm

ofpersuasions

ra ther than proof. In

Bayesian

te rms ,

the

reasons

are

marsha led

in the

guise

of

ptausiblTily

a r g u m e n t s .The d e p l o y m e n tof plausibi l i tya r g u m e n tsis anart form

for which there

current ly exis ts

n o

t axonomy .

A n d

cons ider ing

the

l imitless variety of such a rgumen t s , it isun l i ke ly t h a t a n y t h i n g m o r e

t h a n

asup erf ic ia l t axon om y can be deve loped . E ins te in , the consum -

mate mas te r of th isart fo rm, appea led to analogies), symmet ry con-

s iderat ions ,

thought exper iments , heur i s t ic

principles

such

as

the

pr inc ip le

o f equ iva lence ,

etc.

All of

these

considerat ions, I am sug-


20/29

27

C a r n a p , K u h n , an d the

Ph i lo sophy

o f Scientific

M ethodology

gcs t ing on

be ha l f

of th e

Baycsians ,

were deployed to n udg e a ssign -

m e n t s

of

in i t ia l

probabi l i t ies in

favor

of

the

theories Eins te in was

i n t r o d u c i n g

in the

ear ly

decades

of

this cen tury . E instein 's success

in

this

regard

is no

less important than experimental evidence

in ex-

p l a i n i ng

th e recept ion of his theories.

T o s u m m a r i z e , K u h n ' s pu rp le passages do no t

seem

overb lown

w h e n

applied to revolut ions in the st rong sense d ist inguished

above.

T he persuasions that lead to the adoption of the newshape fo r

the

possibility

space can no t a m ou n t to proofs . Certa in ly for the

Bayesian

they

can no t cons is t o f indu c t iveproofs, since the very

a s signmen t

of

degrees

of

belief

presupposes

the

adoption

of

such

a

space.

After

a

revolut ion has taken place, the newand o ld theories can often be

fi t ted

i n to

a common f r ame tha t be l i e s an y vicious fo rm of i nc o m -

mensurab i l i ty (as I tried to illustrate in section 4 for N e w t o n i a n an d

relativistic theories). But this retrospective

view

tends to disguise the

shake-up in our system of beliefs occasioned by the adoption of the

n ew

shape

fo r

the possibi l i tyspace.Baycs ian i sm b r ing s

the

shake-up

to

l ight , albei t

in a way

tha t unde rcu t s

the

s t anda rd fo rm

o f

the

doctr ine .

I have no way of kn ow in g wh e the r Ca rn ap w ou ld have app roved

of my

B ayes ian read ing

o f

K u h n .

But I do

claim tha t

it is a

read ing

t ha t

fi ts

na tu ra l l y wi th Carnap 's mature v iews

on

probabil i ty

an d

induc t ion .

8 Objectivityand the Problem of

Consensus

I haveendorsed a Bayesianized version of Kuhn ' s c l a im tha t in sci-

enti f ic revolut ions persuasion ra ther than proof is the order o f the

d a y :

revolut ions

involve the in t roduct ion of new possibilities; this

in t roduc t ion causes the redistribution of probabilit ies; the redistri-

but ion isguided b y

plausibi l i ty

a r g u m e n t s ; an d such a rguments be -

long to the art of persuasion.

This

endo r semen t

is

conf ined

to the firststage of the

revolut ion,

when

the

ini t ia l

probabilit ies are established for the expanded pos-

sibility set. The Bayes ian fo lk lo re would have it that after thisfirst

stage, s o m e t h i n g

more

ak in

toproof

than persuasion operates.

The

idea

is

that

an

evidence-driven consensus emerges

as a

result

of the

Bayesian l e a rn ing model:degrees of belief change by conditional -


21/29


22/29

2 )

C a r n a p , K u l i i i , a n d th e Philosophyof

Scienti f ic

Methodo logy

a p robab i l i t y f u n c l i o n . If th i s were

corrccl, ihc liaycsian

ver s ion o f

llie

problem

o f

scicnl i f ic

objectivi ty

would

be

made

correspondingly

easier.

However,

I do not

think

that Carnapmanaged tostakeout a

d e f ens i b l e position, as can be brought out by the question of how

one recognizes wh i ch probability functionsare rational. Carnap's

a n s w e r

w as toappeal towhat

he

variously called inductive

i n t u i l i o n "

and induclivc common

sense.

The trouble, of course, isthat one

person's i n d u c t i v e common sense

is

another's i n duc t i ve non-sense.

So the appea l to i n t u i t i o n reveals

very

diffcrenl opinions as lo

whelhcr

i t is rat ional to

learn from

experience

at all

and,

if so, at

w h a t rate.

A t

th isjuncture

il

wil l

b e

he l p fu l

to

review

a

mechanism

proposed

by L e h r e i an d Wagner in

Ra t i ona l

C o n s e n s u s in Science a n d Society

(1981) for achieving agroupconsensus.Their mechanism requires

t h a t

th e

members of ihc community

change ihcir

degrees o f bel ief

in

accordance wi lh

a

wcighled-aggrcgalion

ru le .

Suppose that

a t

the

i n i t i a l

m o m e n t , person

i has a

degree

o f bel ief /;, in the theory in

question.

Each

person i is

assumed

to

assign

a

weigh t

w/

0 to

every

person

_ ; ' , w h i c h can be

taken

as an index of i ' s

opinion

as to

th e

re l iab i l i ty

of/s opinions. According toLchrcr a n d Wagner's r u l e , i

t he n improves her i n i l i a lopinion /> ? b ychanging it topi = X,w,y/>".

If there arc

still

differences of opinion, the aggregation processis

repeated

w i th

the /;,' to obtain

f u r t h e r

improved probabilities

/;?,

etc., u n t i l e v e n t u a l l y the

probabi l i t ies

for a l l

members

fall

into

l ine .

Lchrcr and

Wagner

o f f e r aconsistencya rg u m e n t for

their

aggre-

ga t ion ru le : If a

person re fuses

toaggregate,

though

hedoes

assign

a

posi t ivew e i g h t

to

other

members,he is

acting

as

though heassigned

aweightof

one

toh imse l fand aweightofzerotoevery

other

member

of

thegroup.If, in fact,he assignspositiveweightto

other

members

of th egroup, ihenheshould nolbeha veas ifheassigned zero we igh t

lo them (1981, 22).Thisargumenthas the flavor of When arc you

going

to

slop b e a t i n gyour

wife ." I d o

assign

a ,

positive weight

to the

o p i n i o n s

of

others,

but as a

liaycsian

I do

this

not by

means

of

weigh ted aggregation b u t

by c on d i t i on a l i z a t i on :

I co nd i t i o na l i zc on

i n f o r m a t i o n about the opinions o f m y

peers,

a n d I notice that th e

result

is a sh i f t in mydegreesof belief toward thedegreesof belief

of those I respect.When I was ayoungstudent,

these shif ts

brought

.m y

opinions

closely in

line

wi th

those

belonging topeople Iregarded


23/29

3

John

lirmun

as the expert s , but as a m at ur e m em ber of the com m un i ty , I f ind

tha t

such

shifts,

whi le

still

n onn egl ig ib lc , do no t

c o n f o rm

m y

o p i n i o n s

lo

those

of

others,

a t

least

no t on mat ters

where

I now

regard myself

as an expert . A n d I res is t any further

a t t em pt

to

bend

m y

careful ly

considered opinions .

There

are tw o

reasons,

i n d e p e n d e n t

o f

Bayes ian ism,

to be

u n h a p p y

with Lehrer an d

Wagner 's proposal

an d ones like i t . The first is

t h a t

it is

descriptively

false, as shown by the very

e x amp l e

they

use

to

motivate the i r proposal. In the 1970s Robert Dicke claimed that

optical

measurement s

of the

solar disk revealed

an

oblateness large

enou g h to accoun t for 3" to 5" of arc in Mercury ' s centenary per i -

helion ad v ance an d thus to throw in to

doubt

Eins te in ' s explanat ion

of

th e

a d v a n c e . W h e n

o th e r

as trophysicis ts disagreed with Dicke ' s

conclusions the

d i f ferences were

n o t

smoothed over

b y

p r od u c ing

a

consensual probabi l i ty

by

means

of a

w eighted aggreg ation process.

The d i s a g reem en t

remains unreso lved

to

this day.

T he

weight

of

op in ion

docs

seem

lo

be

go ing

aga ins t

D icke's in lcrp rc ta t ion , but

this

part ial ag r e e me n t

is in

fact

due not toag gregation but to the acq ui-

sition

of

addi t ional ev idence .

Of course,Lchrcr an d W a g n e r are

perfectly

aw ar e of these facts,

an d

the

descr ip t ive

inadequac ies

of the i r proposal do no t concern

t hem,s ince they

take

them selves to be off er in g a n orm ativeproposal.

B ut

even

in

ihcsc t e r ms

the

proposal should

be

f au l t ed .

It is

f u n d a -

m en ta l

lo science thai opin ions be evidence-dr iven . Differences of

opin ion

need

not

constilutc

an

emb arrassmen t that

needs

lo

be

quashed ,

for ihesc

d i f fe rences

can

serve

as a

spur

lo

fu r the r

iheo-

relical

an d experimental research, and the new in fo rmat ion p ro -

duced may d r ive a gen u in e scientific consensus . The

al ternat ive,

an

a t l cmpl lo m a n u f a c lu r e aconsensus by a w eighted-aggrega tion pro-

cedure, smacks

of the

"mob psychology"

of

which

K u h n w as

criticized.

This

last point generalizes. Bayesianism

an d

other approaches

to

scienlific in fe rence

aswell

suggest that unless

there is

some evidence-

dr iven

process that

operates

on the level of ind iv idualscientists to

produceagroupconsensus ,ihe

consensus willa m o u n l

lo

someth ing

tha t ,

if not mob psychology, is nevertheless a social art ifact not de-

serving ei ther of the labels "rational" or "scienlific."

Thus,

con l rary


24/29

C a r n a p ,

K u l i n ,

a n d

the

Phi losophy of Scientif ic Methodology

to K u h n ' s idea,

th egroupc a n n o t

decideit

can no t r a t ion a l ly dec ide

to

agree if

the i n d i v i d u a l s

disagree.

I do not see how

th is con clus ion

can be escaped

u n l e s ssome

y et tobe a r t icula ted

collcct ivisl m e th o d -

ology is show n lobe viable .

9 A

Partial Resolution

to the Problem ofConsensus

Part of the

an s w e r

to the Bayes ian

version

of the

problem

of

consen-

sus isthat q ui te of ten itdoes n o t exist an d does n o t

need

toexist for

normal sc ient i f ic

research

to

take place.

S t ruc t u r e

warned

of the

d a n -

ger of

t ak ing t ex tbook science as our image of how real

science

actual ly operates,

and in

par t icu lar ,

it

showed

how

textbook science

t e n d s lo m a k e scienti fic r evo l u t i on s

i nv i s ib le

b y p a i n t i n g an ov e r l y

rosy p ic tureof asm ooth ly ac cu m ula t in g s tockp ileof scientific k n o w l -

edge. B u t

I t h i n k t h a t St ruc ture fai led to emphas ize how textbook

science also disguises

the

d ivers i ty of opin ions and approaches that

f lour i sh in n o n r c v o l u t i o n a r y science.

If I had the space, 1w o u l d

o f f e r

as a case s t u d y the

d e v e l op m e n t

of relativisticg r av i t a t ion a lresearch over the last

seven ty-f ive-years .

19

Textbooks

in th is

area

have t ended to

be

books on E in s t e i n ' s G TR ,

t h u s fos ter ing

th e i l lusion t ha t

G T R h a sachieved

the

s tatus of

para -

d igm

h e g e m o n y .

In addi t ion , ear ly textbooks n o t on ly d ow np lay ed

the exis tence o f r ival theories b u t disguised ser ious difficul t ies w i t h

tw o

of

the

p r i nc ip a le x p e r i m e n t al tests ofG T R , the red

shif t

an d

the

b e n d i n g

o f

l ig h t . N o r m a l

scientif ic

research

in

this

field

c o n t in u e d

in

the face of

bo th

a cha l lenge lo the th i rd exper imenta l

leg

o f G T R

d e r i v i n g from D icke' ssolar-oblatenessm easurem en ts and a lso an ever

g r o w i n g n u m b e r o f

r ival theories

o f

gravi tat ion.

This and s im i l a r

e x a m p l e ssuggest

t h a t n o r m a lscience

is possiblew h e n thec o m m u n i ty

ofexperts

share

a

parad igm

in the

weak sense

of

ag r eemen t

on the

ex p l ana t o r y d oma in

of the field, on the

c i rcumscr ip t ion

of the

space

of

possible theories

to be

considered

as

ser ious candidates

for

cov-

ering

the

ex p l ana t o r y d oma in ,

on

exemplars

of

explanatory success,

and on key aux i l i a ryhypotheses. (I am

t empted

to say

tha t this

is the

m i n i m a l

sense o f parad igm needed to

u n d e r w r i t e

normal sc ience ,

b u t h is tor ians o f sc ience probably have counterexamples w a i t i n g in

thewings . )


25/29

John Kaim an

One could a rgue t ha t n o t h a v i n g a pa rad igm in th e stricter sense

of

a shared

theory

of

gravi ta t ion has

lowered

the puzzle-solving

efficiency

of normal science. One can recal lThornca n d Will 's (1971)

l a m e n t

thai , faced wi th

a zoo of

a l tern a t iv e theor ies

of

g r a v i t a t i o n ,

astrophysicists where

hamstrung in thei r model -bui ld ing activity.

While I

t h i n k t ha t this

is a fa ir

observa t ion ,

I

also

t h i n k

tha t there

is

more

toprogressinn o rm a l

science

tha n puzzle solving. In particular,

I would

emphas ize

the conceptua l advances derived f rom

the

explo-

ration of the

space

of

possible theories,

a

po in t tha t br ings

me to the

second part

o f my

par t ia l answer

to the

problem

of

consensus.

Again , if I had the space, I wo uld argue tha t in sofar as a consensus

is

established, it is often due to a

process

akin to the much

maligned

idea of e l imina t ivc i n d u c t i o n . T h is process isoften accomp an ied b y

a proliferation of

theories,

not as an exercise in

Feyerabendian

an-

a rchy

or

D a d a i s m ,

but as a

m e a n s

of

p ro b i n g

the

possibilities

and as

a p r e l i m i n a r yto deve lop ing a classification scheme tha t ma kes sys-

tematic

e l imina t ion

a t ractable

exercise.

20

T he

e l i m i n a t i o n

is no t

of

the s i m p l c m i n d c d Sher lock Holmes var ie ty ,

for it

involves

B ayesian

e lements , especially

in the

assessment

of the

auxi l i a ry a s sumpt ions

needed to b r i n g a b o u t a conf ron ta t ion o f theory an d e x p e r i m e n t .

Thus

the Baycsianizcd versionof the

problem

ofconsensus

remains .

An d a t the p r e sen t

t i m e

I do n ot see any

reso lut ion tha tdoes

n ot

f a l l

back

on s o m e t h i n g l ike the def in i t iona l so lu t ion , which I casually

dismissed in th e preceding sec t ion . Such a fallback un de rm i n es sci-

en t i f i c

objectivi ty

in a way tha t

wo u l d

n o t

have pleased

C a r n a p

a n d ,

I

p r e s u m e , docs n o t please

K u h n

c i t he r .

10

Conclusion

I

was a

d is tan t

s t u d e n t of C a rn a p and a c lose s tudent of K u h n .B u t

the two seemed to me so d i f f er en t in s tyle and concerns that I placed

them in d i f f e ren t pa r t s of the phi losophical f i rmament . O n l y n ow

have

I begun to apprec ia te how mi sgu ided m y p l acemen t was and

how m u c h phi losophyof science can be

enr iched

b ycons ider ing how

the ideas of these tw o gian ts in terac t . I have

presented

one way to

stage the in terac t ion .There are su rely bet ter ones. Iurge more able

hands

to

take

up the task.

21


26/29

33

C a r n a p , K u l i n , an d

th e

Phi losophy

of Scientific

Methodology

Notes

Sections6-9

of

th is

paper arc

earman - carnap, kuhn, and the philosophy of scientific methodology

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