dretske 1971
TRANSCRIPT
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Australasian Journa l o f Philosophy
Vol. 49, No. 1; May, 1971
FRED DRErSKE
C O N C L U S I V E R E A S O N S *
Conc lus iv e r ea sons have a mo da l a s we l l a s an ep i s t emic cha rac t e r . In
hav ing conc lu s ive r ea sons t o be l i eve t ha t P i s t he ca se one s ep i s t emic c reden-
t ia l s a re such a s t o e lim ina t e t he poss ib i l i t y o f mi s t ake . Th i s , a t l ea s t , is
h o w I p r o p o s e t o u n d e r s t a n d t h e m f o r t h e r e m a i n d e r o f t h is p a p e r . L e t t i n g
t h e s y m b o l ( ) r e p r e s e n t t he a p p r o p r i a t e m o d a l i t y ( a y e t t o b e c l ar i fi e d se n se
o f possibility , I sha l l say , t hen , t ha t R i s a conc lus ive r ea so n fo r P i f and
only i f , g iven R, ~ ( ) ,-~ P (or , a l te rna t ive ly , ~ ( ) (R . ~ P)) . This inter-
p r e t a t i o n a l lo w s u s t o s a y o f a n y s u b je c t, S , w h o b e l ie v es t h a t P a n d w h o h a s
conc lus ive r ea sons fo r be l i ev ing tha t P , t ha t , g iven the se r ea sons , h e couM
not be wrong abou t P o r , g iven the se r ea sons , i t is false that he might be
mistaken a b o u t P .
S u p p o s e , t h e n , t h a t
( I ) S kno ws th a t P and h e know s th i s on t he ba s i s ( s imply) o f R en ta i l s
(2 ) R w ould no t be t he ca se un l e ss P we re t he ca se . 1
The l a t t e r fo rmula expre sse s a connec t ion be tween R and P which i s s t rong
enough , I submi t , t o pe rmi t us t o say t ha t i f (2 ) i s t rue , t hen R i s a conc lus ive
rea son fo r P . Fo r i f (2 ) i s t rue , we a re en ti t l ed , no t on ly t o deny tha t , g iven R ,
n o t - P is t h e c a s e, b u t a l s o t h a t , g i v e n R , n o t - P might be the ca se . Tha t i s t o
say , (2 ) e l im ina t e s R an d no t -P a s a poss ib l e ( j o in t ) s t a te o f a f f a ir s and , w hen
we a re given R, i t e l im ina t e s no t - P a s a poss ib l e s t a t e o f a f f ai r s . Th i s i s so
because (2 ) en t a i l s t he f a l s i t y o f ,
(3 ) Al though R i s t he ca se P migh t no t be t he ca se .
I f we expre ss (3 ) a s Giv en R , ( ) ,-~ P , t hen (2 ) en t a i l s t ha t i t is f al se t ha t,
g iven R , ( ) ~ P which is equ iva l e n t t o , g iven R , ~ ( ) ~ P ; and th is i s
p rec i se ly t he r equ i red f ea tu re o f conc lus ive r ea sons g iven above . Hence ,
when (2 ) i s t rue , R i s a conc lus ive r ea son fo r P .
W h a t f o l l o w s is a n am p l i f i c a ti o n o f t h e a b o v e s k e t c h - - h e n c e , a n a r g u m e n t
fo r t he v i ew tha t i n t hose ca ses whe re kno wledg e t ha t P r e s t s on ev idence ,
*An early version o f this paper was read to the P hilosophy Department at The Uni-
versity of Illinois, Chicago Circle. Mo re recently it was read at Th e University o f No rth
Carolina s Colloquium in Philosophy with Professor Robert Sleigh commenting.
x I shall be using R and P to replace a variety of related gram matical units. Depen ding
on the sentential context, they sometimes serve as no un phrases, sometimes as full
indicative sentences, sometimes for appropriate transformations of the indicative.
Fred Dre t ske
gr ounds , o r r ea sons , whe n the que s t ion How doe s S know ? c a n se ns ib ly
be asked and answered, the evidence , grounds , or reasons mus t be conc lus ive .
Any th ing sho r t o f c onc lus ive r e a sons , t hough i t m a y p r ov ide one wi th
jus t i fied t rue be l ie fs , f ai l s to g ive the k ind of suppo r t requis i te to knowledge .
I sha l l a lso urge tha t the possess ion of conc lus ive reasons to be l ieve , prope r ly
qualif ied, is a lso a suff icient condition for knowledge.
1 Knowing P on the Bas i s o f R: The Connec t ion Be tween (1) a n d (2).
Suppose S , in order to assure h imse lf tha t h is chi ld s tempe ra ture i s
norm al (no fever ), p laces a the rm ome ter in the chi ld s mou th , ext rac ts i t
a f te r severa l minutes , and observes a reading of 98.6 F . In remarkin g to the
doc tor tha t h is chi ld s tempe ra ture i s normal S is asked ho w he know s.
S responds , na tura l ly enough, by saying, I jus t t ook his tempera tu re .
Le t us assume, then, tha t w e have an ins tant ia t ion of (1):
( la ) S knows tha t h is chi ld s tempe ra ture i s norm al and he know s th is
on the ba si s o f t he ( no r m a l ) r e a d ing on the the r m om e te r ( wh ic h
he has jus t p laced in the chi ld s mo uth , e tc .) .
Can one consis tent ly a f f i rm ( la ) and deny the cor responding ins tant ia t ion of
(2)?
(2a) The therm ome ter wou ld not have rea d 98.6 unless the chi ld s
t e m pe r a tu r e wa s no r m a l .
I f i t i s not a l ready obvious tha t one cannot consis tent ly a f f i rm ( la ) and deny
(2a) , I th ink i t can be made obvious by consider ing the k ind of th ing which
would sh ow (2a) to be false . Fo r example , i f Char les, f amil ia r wi th the
par t icula r the rm om eter in quest ion, should say, Oh, I know th a t the r -
mom eter ; i t i s f ai r ly accura te for tempera t ures be low 98 but i t s t icks a t
98.6 for a lmos t any higher tempera ture , we have been given sol id grounds f or
re jec t ing (2a) . S imul taneously , however , we have been given sol id grounds
for re jec t ing ( la ) . I f it is that kind of the rmom eter , then i f S s only bas is for
th inking his chi ld s tempe ra ture no rmal i s a 98.6 reading on i t , then he does
n o t k n o w tha t h is child s tempera tu re is normal . I t mi ht be no r m a l , o f
course , but i f S know s tha t i t is , he must h ave more to go o n than the reading
on th is (defec t ive) the rmo meter .
Other a t tempts to show (2a) fa lse have the same e f fec t ; they immedia te ly
undermine R ( the reading on the the rmometer ) as an adequa te bas is for
someon e s knowin g tha t the chi ld s tempe ra ture i s normal (P) . Fo r in
re jec ting (2a) we re jec t the th e rmo meter as a re l iable device for d iscover ing
whether a person s tem pera ture i s normal , an d know ledge is not acquired
by re ly ing on what i s unre liable in prec ise ly those respec ts in which we re ly
on it .
We f requent ly purp or t to know things on the bas is of tes t imony. James
has a la rge s tamp col lec t ion and, a f te r g iv ing a de ta i led descr ip t ion of i t ,
invites S to his hom e to see i t . S declines, but he later refers to Jam es stam p
col lec t ion in conversa t ion. I t is easy enoug h to imagine c i rcumstances in
which i t would be na tura l for som eone to ask S how he knew, wha t reasons
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Conc l us i ve R easons
h e h a d f o r t h i n k i n g , t h a t J a m e s h a d s u c h a c o l l ec t i o n. A n d i t i s j u s t a s e a s y
t o i m a g i n e S , i n r e s p o n s e t o s u c h a q u e r y , r e f e r r i n g t o h i s c o n v e r s a t i o n w i t h
J a m e s . L e t u s a s s u m e , t h e n , t h a t
( l b ) S k n o w s t h a t J a m e s h a s a s t a m p c o l l e c t i o n a n d h e k n o w s t h i s o n th e
b a s is o f J a m e s ' d e s c r i p t i o n ( a n d i n v i t a t i o n )
i s t r ue . I a m n o t n o w c o n c e r n e d t o a r g u e t h a t o n e c a n k n o w s o m e t h i n g
o f th i s s o r t in t h i s w a y ; t h e q u e s t i o n i s, r a th e r , w h e t h e r ( 2 b ) m u s t b e t r u e / f
( lb ) i s t rue .
( 2 b ) J a m e s w o u l d n o t h a v e s a i d h e h a d a s t a m p c o l l e c t i o n , d e s c r i b e d
i t i n s uc h de ta i l , a nd i s s ue d a n inv i t a t ion un le s s he ha d a s t a mp
c o l l e c t ion .
I f Ja m e s i s t h e s o r t o f f e l lo w a b o u t w h i c h ( 2 b ) c a n n o t b e t r u l y a ss e r t ed , t h e n
h e is n o t t h e s o r t o f fe l lo w w h o c a n b e t r u s t e d o n s u c h m a t t e r s a s th i s. I f
J a m e s i s th e s o r t o f f el l o w w h o s o m e t i m e s s a y s s u c h t h i n g s a s a j o k e , w h o
w o u l d ( o r m i g h t ) c o n c o c t su c h e l a b o r a t e s t or i e s f o r h i s o w n a m u s e m e n t
( o r w h a t e v er ) , w h o w o u l d ( o r m i g h t ) w h i m s i c a l l y i ss u e a n i n v i t a t i o n o f t hi s
s o r t und e r to t a l ly fa l se p re t e x t s , t he n , de s p i t e the fa c t t ha t he i s (by hypo -
the s i s ) t e l l i ng the t ru th on th i s oc c a s ion , h i s t e s t imony i s ha rd ly the s o r t on
w h i c h o n e c a n re s t a c l a im t o k n o w . I n d e n y i n g ( 2 b ) o n e i s c o n c e d i n g t h a t
J a m e s w o u l d , o r m i g h t , h a v e s a i d w h a t h e d i d w i t h o u t p o s s e s s i n g a s t a m p
c o l l e c t ion , a nd in the l igh t o f th i s c onc e s s ion one c a nn o t g o on to in s i s t t ha t ,
none the le s s , S
k n o w s
he ha s a s t a mp c o l l e c t ion on the ba s i s, s imp ly , o f wha t
J a me s s a id .
I n a r e c e n t ar t ic l e G i l b e r t H a r m a n c o n t r a s t s t w o c a s es ,
t he l o t t e ry case
a n d t he t e s t i mon y case . 2 A l t h o u g h S , s ay , h as o n l y o n e a m o n g t h o u s a n d s o f
t i c ke t s in a lo t t e ry a nd , he nc e , ha s a n e x t re me ly s l e nde r c h a nc e o f w inn ing ,
w e n a t u r a l l y r e j e c t th e i d e a t h a t S c o u l d k n o w t h a t h e w a s g o i n g t o l o s e o n t h e
ba s i s o f a c o r re c t p rob a b i l i t y e s t ima te (we l l ove r 99 .9 ) o f h i s lo s ing . Eve n
i f S c o r r e c t l y p r e d ic t s t h a t h e i s g o i n g t o l o se , w e w o u l d d e n y t h a t h e k n e w h e
wa s g o ing to lo s e i f t he onl y ba s i s he ha d fo r th i s be l i e f wa s the fa c t t h a t h i s
c h a n c e s o f w i n n i n g w e r e s o s l i gh t , s H a r m a n c o m p a r e s t h is c a s e w i t h t h e
s i t u a t io n i n w h i c h w e o f t e n s e e m p r e p a r e d t o s a y t h a t S k n o w s t h a t P w h e n
h e i s t o l d t h a t P i s t h e c as e b y s o m e o t h e r p e r s o n ( t e s t i m o n y c a se ) . A l t h o u g h
p r o b a b i l i t y e s t i m a t e s a r e n o t a l t o g e t h e r a p p r o p r i a t e h e r e , w e d o k n o w t h a t
p e o p l e s o m e t i m e s l ie , so m e t i m e s t h e y a r e h o n e s t l y m i s t ak e n , a n d s o o n .
The re a lwa ys s e e ms to be a c ha nc e tha t wha t a pe r s on t e l l s u s i s no t the c a s e
h o w e v e r s in c e r e o r c r ed i b l e h e m a y a p p e a r , a n d t h e o r d e r o f m a g n i t u d e o f
2 'Knowledge, Inference, and Explanation', in American Philosophical Quarterly July,
1968.
8 Of course S m ay have said ' I kno w I am going to lose' and he may say now, after he has
lost, 'I knew I was going to lose', but these expressions are normally accepted without
epistemological quibbling because the y are taken as little more th an expressions of resig-
nation o r despair. With this use of the verb 'to know ', one can know one is going to
lose and
still
spend a dollar for a ticket and a chance at the prize---a fact about human
beings which is puzzling if they believe they know (in any epistemologically relevant
sense) that they are going to lose.
3
Fred Dretske
t h i s c h a n c e s e e m s t o b e c o m p a r a b l e t o t h e c h a n c e w e m i g h t w i n i n s o m e
a p p r o p r i a t e l o t te r y s i t u a ti o n . W h y , t h e n , a r e w e p r e p a r e d t o s a y t h a t w e
k n o w i n t h e o n e c a s e b u t n o t in th e o t h e r ? H a r m a n h a s s o m e r e v e a l i n g
r e m a r k s t o m a k e a b o u t t h e s e c a s e s, b u t I m e n t i o n t h e m o n l y t o b ri n g o u t
t h e i r r e l e v a n c e t o t h e p r e s e n t d is c u s s i o n . F o r I t h in k t h i s c o n t r a s t s t r e n g t h e n s
t h e v i e w t h a t ( 2 ) i s n o r m a l l y a c c e p t e d a s a n e c e s s a r y c o n s e q u e n c e o f (1 ) ,
t h a t w h e n w e a r e u n w i ll i n g t o e n d o r s e t h e c o r r e s p o n d i n g i n s t a n t i a t i o n o f
( 2 ) w e a r e u n w i l l i n g t o t a l k o f a n y o n e k n o w i n g t h a t P i s th e c a s e o n t h e b a s i s
o f t h e e v id e n c e e x p re s s e d b y R . I n m a n y t e s t i m o n y s i t u a t i o n s w e a r e , I
b e l i e v e , w i l l i n g t o a f f i r m ( 2 ) : th e p e r s o n w o u l d n o t h a v e s a i d i t u n l e s s i t w a s
s o . I n t h e l o t t e r y c a s e, h o w e v e r , t h e c o n n e c t i o n b e t w e e n R a n d P e x p r e s s e d
b y t h i s s u b j u n c t i v e c o n d i t i o n a l f a i ls t o b e r e a li z e d , a n d i t f a il s n o m a t t e r h o w
g r e a t t h e p r o b a b i l i t i e s b e c o m e . A d j u s t i n g t h e w o r d i n g o f (2 ) to s u i t t h e
e x a m p l e i n q u e s t i o n 4 w e h a v e
( 2 c) I f S w e re g o i n g t o w i n t h e l o t t e r y , h is c h a n c e s o f w i n n i n g w o u l d
n o t b e 1 / m ( m b e i n g t h e n u m b e r o f ti c k e t s s o l d) .
W h a t e v e r ( f in i te ) v a l u e w e g i v e t o m , w e k n o w t h i s i s f a ls e s i n c e s o m e o n e
w h o s e c h a n c e s o f w i n n i n g a r e 1 / m will w i n , a n d s i n c e t h e r e i s n o t h i n g s p e c i a l
a b o u t S w h i c h w o u l d r e q u i r e h i m t o h a v e a b e t t e r c h a n c e o f w i n n i n g t h a n
a n y o n e e l s e i n o r d e r t o w i n , w e r e j e c t ( 2 c ) a s f a l s e. H e n c e , w e r e j e c t t h e i d e a
t h a t S c a n k n o w h e i s g o i n g t o l o s e o n t h e b a s i s o f th e f a c t t h a t h i s c h a n c e s o f
l o s i n g a r e ( m - 1 ) / m .
A l v i n G o l d m a n , i n d e v e l o p i n g a c a u s a l a c c o u n t o f k n o w l e d g e , c o n s t r u c t s a
s i t u a t i o n i n w h i c h S i s s a i d to k n o w t h a t a n e a r b y m o u n t a i n ( I w il l c a l l i t M )
e r u p t e d m a n y y e a r s a g o . H e k n o w s t h i s o n t h e b as i s o f t h e p re s e n c e o f
s o l i di f i ed l a v a t h r o u g h o u t t h e c o u n t r y s i d e s u r r o u n d i n g t h e m o u n t a i n . 5
A c c o r d i n g t o G o l d m a n , a n e c e s s a r y c o n d i t i o n f o r S s k n o w i n g t h a t M
e r u p t e d m a n y y e a r s a g o o n t h e b a s i s o f th e p r e s e n t e x i s te n c e a n d d i s t r i b u t i o n
o f t h e la v a i s t h a t t h e r e b e a c a u s a l c o n n e c t i o n b e t w e e n t h e e r u p t i o n o f t h e
m o u n t a i n a n d t h e p r e s e n t e x i st e n c e a n d d i s t r i b u t i o n o f t h e l a v a . I d o n o t
4 The wording o f (2) will sometimes have to b e adjusted to suit the part icular instantiat ion
in question. The chief factors determining this adjustment are the relat ive temporal
locations of R, P and the t ime of utterance and also the causal connections, if any, which
are believed to hold between R and P. The part icu lar wording I have given (2) is most
appropriate when P is some state of affairs antecedent to (or contemporaneous with)
both R and the t ime of utterance. This, of course, is the result of the fact that (2) is
most o ften used when P is som e state o f affairs causally responsible for the present
condit ion R. When P is a future state we might express (2) as: R would not be the case
unless P were going to happen . For exam ple, he would not have registered unless he
were going to vote. I do no t wish to preclude the possibili ty of knowing that something
will
occur on the basis of present evidence by restricting the wording of (2). The
difficulty, of course, is that when P is some future state, the subjunctive relating it to R
generally becomes somewhat questionable. We prefer to say, in our mo re cautious
moods, th at if he were not planningto vote, he w ould not have registered (acknowledging,
thereby, the fact that contingencies may interfere with the execution of his plans).
But in the same cautious mood s we prefer to say, not that we know he is going to vote
(because he registered), but that we kno w he plans or intends to vote.
A Causal Theory of Knowing ,
Journal of Philosophy
Jane 22, 1967, p. 361.
4
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Conclusive Reasons
wish to d ispu te th i s c la im a t the m om en t s ince the v iew I am advanc ing i s even
s t ronger : viz t h a t a n eces s a r y co n d i t io n f o r S t o k n o w t h a t M e r u p t ed o n
this basis is that
(2d) The lava would no t be here , and d is t r ibu ted in th i s man ner , un less
M e r u p t ed
is t rue . (2d) i s a s t ronger c la im than tha t the eru p t ion o f M is causal ly
connected wi th the p resen t ex is tence and d is t r ibu t ion o f the lava . (2d) r e-
qu i res , in add i t ion , th a t M s erup t ion be n ecessary fo r the p resen t s ta te o f
af fa i rs . To i l lus t r a te , cons ider the fo l lowing embe l l i shmen t on G old ma n s
ex am p l e. N o t f a r f r o m M is an o t h e r m o u n t a i n , N . T h e g eo lo g y o f t h e
area i s such tha t a t the po in t in t ime a t which M erup ted someth ing , so to
speak , was boun d to g ive; i f M had no t erup ted , N would have . Fur the r -
more , the locat ion o f N is such tha t i f i t , r a ther th an M, had erup ted , the
presen t d i s t r ibu t ion o f lava would h ave been , in a l l r espects re levan t to S s
tak ing it as a r eason fo r be l iev ing M erup ted , the sam e. In such c i r cum-
s tances Gold ma n s necessary condi t ion i s sa t i sf ied , bu t mine i s no t . (2d) is
f a l se ; it is f a lse tha t the lava wo uld no t be here , a nd d is t r ibu ted in th i s f ash ion ,
un less M had erup ted . Fo r if , con t r ary to hypothes is , M had no t erup ted ,
N would have; leav ing the very same ( r e levan t ) t r aces .
In such c i r cumstances I do no t th ink we cou ld say tha t S knew that M
erup ted on the bas i s o f the p resen t ex is tence and d is t r ibu t ion o f lava . For ,
by hypothes is ,
this
s ta te o f af f a i r s would hav e ob ta ined w hether M erup te d
or no t and , h ence , there i s no th in g ab out th i s s ta te o f af f a i rs which f avo ur s
one hypothes is (M erup ted) over a comp et ing hypothes is (N erup ted) . S
is s t i l l co r r ec t in suppos ing tha t M d id erup t , s t i l l co r r ec t in suppos ing tha t
i t was M s erup t ion which i s causal ly r espons ib le fo r the p resen t ex is tence
an d d i s t r i b u ti o n o f l av a , b u t h e d o es n o t k n o w i t w as M t h a t e r u p t ed - - n o t
u n le s s h e h as s o m e ad d i t i o n a l g r o u n d s w h i ch p r ec lu d e N . I f h e h as s u ch
ad d i t i o na l g r o u n d s , c a ll t h em Q , t h en w e can s ay t h a t h e k n o w s t h a t M
erup ted and he knows th is on the bas i s o f
R and Q
In th i s case , however ,
the cor resp ondin g ins tan t ia t ion o f (2 ) is a l so sa t is f ied : R
and
Q w o u l d n o t
be the case un less M erup ted . As th ings s tand , the mos t tha t S cou ld know,
on the bas i s s imply o f the p resen t ex is tence and d is t r ibu t ion o f lava , i s tha t
either M o r N erup ted
( 2) p e r m i t s u s t o s ay th i s m u ch , an d n o m o r e , ab o u t
w h a t can b e k n o w n o n t h e b as i s o f l av a fl o w.
T h e ca s e b eco m es ev en c lea r e r i f w e ex p l o it an o t h e r o f H a r m an s ex am p l es .6
Har o ld has a t i cket in a lo t tery . The od ds agains t h i s winn ing are 10 ,000 to 1 .
T h e p r i ze , c a l l i t an X , i s s o m e t h i n g t h a t H a r o l d d o es n o t n o w h av e n o r
co u l d h e r ea s o n ab l y ex p ec t t o o b t a i n o n e b y m ean s o t h e r t h an w i n n i n g t h e
l o t te r y . E n t e r a p h i lan t h r o p i c g en t l em an , R o ck a f o r d , w h o d ec i d es t o g i ve
Ha ro ld an X i f ( as seems l ike ly ) he shou ld f a i l to win on e in the lo t tery .
T h i n g s 3 o a s o n e w o u l d ex p ec t ; H a r o l d h o l d s a l o si n g t i ck e t . R o ck a f o r d
k eep s hi s w o r d a n d g i v es H ar o l d a n X . S , f am i l i a r w i t h t h e ab o v e c i r cu m -
s t ances b u t u n aw ar e o f w h e t h e r H a r o l d w o n o r l o s t i n t h e l o t te r y , f in d s
o In Knowledge, Inference, and Explanation , pp. 168-9. I have adapted the example
somewhat.
Fred D re tske
Haro ld with his newly acquired X. S infers that Haro ld received his X from
Roekafo rd. He concludes this because he knows that the only other way
Harold might have acquired an X is by winning the lottery and the odds
g inst that happening are enormous. The following conditions are satis-
fied: (a) Harold received his X from Rockaford; (b) S believes that Harold
received his X from Rockaford; (c) S is warranted in believing this since the
chances of his having received it in any other way are negligible; (d) Rocka-
ford s generous gift of an X to Haro ld is the (causal ?) explanation of Harol d s
present possession of an X; and, finally (e) S correctly reconstructs (to use
Gold man s language) the causal chain o f events which brough t ab out
Harold s possession of an X. Yet, why does it seem clear (at least to myself---
and apparently to Harman) and S does n o t know that Rockaford gave
Haro ld his X. Because
(2e) Harold would not have an X unless Rockaford gave him one
is plainly false.7 If Rock afo rd had not given him an X, it would have been
because Harold already possessed one as a winner in the lottery. Hence,
Harold would possess an X even if Rockaford had not given him one.
It is not true that R would not be the case
unless
P; hence, not true that S
knows t hat P on the basis of R. s
(2), therefore, expresses something stronger than a causal relationship
between R and P. It should be pointed out, however, that it expresses
something which is, in certain important respects, weaker than a universal
association between states or conditions similar to R and states or condit ions
similar to P. When R and P are expressions which stand for particular
conditions or states of affairs, as will often be the case when we know one
thing on the basis of something else, (2) expresses a connection between more
d e t e r m i n a t e
states of affairs than those described by talking about states
similar to R and P. If someone remarks, mid-way throug h a poker hand,
that if his neighbour had not folded (dropped from the game) he (the speaker)
would have been dealt a royal flush, he is obviously not maintaining that
whenever his neighbour remains in the game, he (the speaker) is rewarded
with a royal flush. Rather , he is talking about
this
hand (already holding
four cards to the royal flush), this part icular distribution of cards in the
remainder of the deck, this part icular seating arrangement, and so on.
He is not saying that his neig hbou r s remaining in the game is, quite generally,
sufficient for his receipt of a royal flush. Rather , he is saying that in the
7 There is a way of reading (2e) which makes it sound true--viz if we illicitly smuggle in
the fact that Harold
has lost
the lottery. That is, (2e ) Harold, having lost the lottery,
would not have an X unless Rockaford had given him one , is true. But this version of
(2) makes R, the reason S has for believing Rockaford gave him an X, not only Harold s
possession of an X but also
his having lost th e lottery.
This, by hypothesis, is not part
of S s reason; hence, not properly included in (2e). (2e) must be read in something like
the followingfashion: Harold would not have an X, whatever the outcome of the lottery,
unless Rockaford had given him one. With this reading it is clearly false.
s It is difficult to say whether this is a counter-example to Goldman s analysis. I think it
satisfies all the conditions he catalogues as sufficient for knowledge, but this depends on
how strictly Goldman intends the condition that S must be warranted in inferring that
P is the case from R.
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Conclus ive Reasons
part icular c ircumstances which in fa ct prevai led on this occasion,
circumstances
which include such things as car d distribution, arrange ment of players, etc.,
an occurrence of the first sort (neighbour remains in game) will invariably
be followed by one of the second sort (his receipt of a royal flush). One
cannot falsify his claim by showing that he would not have received a royal
flush, despite his neighbour's remaining in the game, if the card distribution
in the deck had been different from what it in fact was. Fo r his claim was a
claim about the inevitable sequence of events with that dis tr ibut ion of cards .
Statements such as (2), then, even when R and P are expressions for par-
ticular states of affairs, express a general uniformity, but this general uni-
formity is not that whenever a state similar to R is the case, then a state
similar to P will also be (or have been) the case. The uni form ity in question
concerns the relationship between states similar to R and P under a f i xed
set of c ircumstances . Whenever (a state such as) R in c ircumstances C then
(a state such as) P where the circumstances C are defined in terms of those
circumstances which actually prevail on the occasion of R and P. But does
C include
all
the circumstances that prevail on the occasion in question or
only some of these? Clearly not all the circumstances since this would
trivialize every subjunctive condi tion al of this sort. Even if we restrict C
to only those circumstances logically independent of R and P we still obtain
a trivialization. For, to use Goldma n's mountai n example (as embellished),
C would still include the fact that N did not erupt (since this is logically
independent o f both R and P), and this is obviously one of the circumstances
not held fixed when we say that the lava would not be here unless M erupted.
For in asserting his subjunctive we mean to be asserting something which
would be
f a l s e
in the situation described (N would have erupted if M had
not) whereas if we hold this circumstance (N did not erupt) fixed, the uni-
formity between the presence of lava and M's eruption would
hold.
I think that our examples, not to mention an extensive literature on the
subject, 9 point the way to a prop er interpretation of C. The circumstances
which are assumed constant, which are tacitly held fixed, in conditionals
such as (2), are those circumstances prevailing on the occasion in question
(the occasion on and between which the particular states R and P obtain)
which are logically and causally independent of the state of affairs expressed
9 I am not proposing a solution to the problem to which Nelson Goodman Fact, Fiction
and Forecast,
Chapter I), Roderick Chisholm ('The Contrary-to-Fact Conditional,
Mind, 55, 1946) and others addressed themselves in trying to specify the 'relevant con-
ditions' associated with counterfactuals. I shall use the notion of 'causality' in my
treatment, a device which both Goodman and Chisholm would regard as question-
begging. I am not, however, attempting to offer an extensionalist analysis of the sub-
junctive conditional; I am merely trying to get clear in what way such conditionals are
stronger than the statement of a causal relationship between R and P and yet (in one
sense) weaker than a statement of the universal association between states similar to
Rand P.
Fred retske
by p.10 Wh en we have a s ta te ment in the sub junct ive which (un l ike (2 ))
i s counter f ac tual ( the an teceden t g ives express ion to a s ta te o f af f a i r s which
does o r d id no t ob ta in ) , then C inc ludes those c ir cumstances p revai l ing on the
occas ion which are log ica lly and causal ly independe nt o f the s ta te o f af f a ir s
(o r lack o f such s ta te) expressed by the antecedent of the condi t ional . In
o u r p o k e r g am e , f o r ex am p l e , w e can s ay t h a t S s s t a t em en t ( I w o u ld h av e
got a royal f lush i f my n eighbou r had s tayed in the game) f i x e s tha t se t o f
c i r cumstances which are log ica l ly and causal ly indepen dent o f h i s ne ighb our s
s tay ing in the gam e ( i .e . the an teceden t s ince the s ta tement i s c ounter f ac tual ) .
Hence , i f there i s ano ther p lay er in the game (whose p resence o r absence
af fects the cards deal t to S) who w ould h ave d ropp ed i f S s ne ighbo ur had
not d ro pped , then th i s per son s r ema in ing in the game i s not held f ixed, not
inc luded in C, be cause i t i s causal ly connected to the s ta te o f af f a ir s expressed
by the an teceden t in S s s ta tement . Therefore , we can show S s s ta teme nt
to be f a l se i f we can show that such a c i r cumstance p revai led , and i t is a long
these l ines tha t one would sure ly argue in a t tempt ing to show S tha t he
was wrong , wrong in say ing tha t he would have r eceived a royal f lush i f h i s
neighbour had s tayed in the game.
On the o ther hand , one cann ot show tha t S s s ta tement i s f a l se by showing
that , were the cards d i f f eren t ly ar r ange d in the r ema inder o f the deck , he
would no t have r eceived h is royal f lush ; fo r the ar r angement o f cards in the
remain der o f the deck (un like the p resence o r absence o f our o ther p layer )
i s (p resumably) indepe ndent o f S s ne ighbou r s de par tu re f rom the game.
Hence , i t i s one o f the condi t ions held f ixed , inc luded in C, b y S s s ta tement ,
and we are no t a l lowed to cons ider a l te r a t ions in i t in assess ing the genera l
impl ica t ion o f S s s ta tement .
Or cons ider our o r ig inal therm ome ter example . Recal l , the s ta tement in
ques t ion was : The th ermo me ter would n o t have r ead 98 .6 un less the ch i ld s
t em p er a t u r e w as n o r m a l . Su p p o s e s o m eo n e r e s p o n ds , O h , i t w o u l d h av e
( o r m i g h t h av e) i f t h e t h e r m o m et e r w as b r o k en . I t is i m p o r t an t t o u n d e r -
s t an d t h a t o n e can g r an t t h e t r u t h o f t h is r e s p o n s e w i t h o u t ab an d o n i n g t h e
or ig inal asser t ion ; fo r the o r ig inal asser t ion had , as i t s genera l impl ica t ion ,
not a s ta te ment express ing a un i fo rm re la t ionsh ip between s ta tes o f af f a ir s
s i m il a r t o t h e ch i l d s t em p er a t u r e ( n o r m a l b o d y t em p er a t u r e ) an d s t at e s o f
af f a i r s s imi lar to the thermometer r ead ing ( a r ead ing of 98.6 , but , r a ther , a
un i fo rmi ty between such s ta tes
under a f ix ed set o f c ircumstances.
A n d , i f
10 This character izat ion of the c ircumstances C has interest ing and, I bel ieve, s ignif icant
repercussions for subjunct ives having the form of (2) in which R expresses some present
(or past) s ta te of affa irs and P expresses some future s ta te of affa irs . Alt hou gh I lack the
space to discuss the point here , I bel ieve an important asymmetry is generated by a shif t
in the re la t ive tempo ral locat ions of R a nd P. I a lso believe, however , tha t th is asym -
metry is fa i thful ly ref lected in the difference between knowing what
will
h a p p e n o n t h e
bas i s o f p re sen t da ta and knowing wha t did happen on the bas i s o f p re sen t da ta . In
other words, I feel that an asymmetry in (2) , ar is ing from a shif t in the re la t ive tem-
poral locat ions of R and P, helps one to understand the difference we al l feel between
knowing , on the one hand , wha t d id happen o r i s happen ing , and , on the o the r hand ,
what wil l happen.
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Conclusive Reasons
I am fight, this f ixed set of circums tances inclu des the actual s tate of the
thermometer
(defec tive or accura te ) ; i t i s one o f those c i rcumstances preva i l ing
on the occas ion in quest ion which is causa l ly and logica l ly indep enden t of
the chi ld s tempera ture . Hence , th is c i rcumstance canno t be a l lowed to
vary as i t i s in the above response by the words i f the the r mom eter was
broken . To de te rmin e the t ru th of the or ig ina l asse r t ion we must sup pose
tha t the the rm ome ter i s accura te (or defec t ive) whatever the actua l condition is.
I f , the re fore, the the rmom eter was no t bro ken o r o therwise defec tive on th a t
occas ion, then the suggest ion tha t i t would (or might) have read the same
despite a feverish child if i t were broken or defective is, a lthough quite true,
i r re levant to the t ru t h o f the s ta tement : I t would n ot have read 98.6 unless
the child s tempe ra ture was n ormal .
One f ina l imp or tan t fea ture of (2). I have said tha t , genera l ly speaking,
the p lace-holders R and P represent express ions des igna t ing
specific
states
of affairs or condit ions. Wh en this is so, (2) stil l has a general implicatio n,
but the genera l impl ica t ion, express ing a uniform re la t ionship be tween
states of affairs similar to R and P, has its scope restricted to s i tua t ions in
which the circums tances C (as specif ied abov e) obtain. Since we are talking
about specif ic states of affairs in most instantiations of (2) , i t becomes
extremely imp or tan t to observe the sor ts of re fe r ring express ions embodie d
within bot h R and P . Fo r example , when I say , Joh n would not have sa id
i t was rain ing unless i t was ra in ing I am ta lk ing abou t
John
a nd a bou t a
particular utterance of his. Someone else might have sa id th is wi thout i t s
be ing t rue ; Jo hn m ay have sa id something else withou t i t s be ing t rue . Non e-
theless,
John
would n o t ha ve sa id
it was raining
unless i t was . An incurable
l ia r abou t most th ings, John has a pa thologica l devot io n to accuracy on
mat te r s concerning the wea ther . In such a case, a l though John is, admit tedly ,
a most unre l iable informant on most mat te r s , we can say tha t he would
not have sa id i t was ra in ing unless i t was so . This i s only to say tha t the
re fe rr ing express ions to be foun d in R and P help to define the scope o f
the impl ied genera l iza t ion. Reca l l, the impl ied genera l iza t ion was about
states of affairs similar to ( the par t icula r s ta tes) R and P . S imila r in wha t
respec t? The sor t of re fe r r ing express ions to be foun d wi thin R and P
he lp us to answer th is ques t ion. In the case of Joh n above , the genera l
impl ica t ion involved, not
a person s say ing something
(under c i rcumstances
C), not John s saying something (under c i rcumstances C) , but Joh n s saying
something about the wea ther (under c i rcumstances C) .
2. The Possibi l i ty of Mistake: The C onnection Between
(2)
and
(3).
Takin g a cue f rom the fac t tha t (2) expresses some form of necessa ry re -
la t ionship be tween R and P , I have ( in my open ing remarks) expressed (2) as :
Gi ven R, -,~ ( ) ,-~ P (or, altern ative ly, , ,~ ( ) ( R . --~ P)). I th ink th e full
justif ication for expressing (2) in this fashion lies in the fact that (2) and (3)
a re contradic tor ies , and s ince (3) may be rendered as :
(3) Given R, () ~ P (or , a lternatively , ( )( R . ,-~ P)
(2) ma y be represented as Giv en R, ,,~ () ,,~ P .
Fred Dre t ske
To see tha t th i s i s so , i t should be not i ced tha t in denying the connec t ion
be t w e e n R a nd P e xp r e s s e d by ( 2 ) w e do no t c om m i t ou r s e l ve s t o a ny t h i ng
as s t rong as :
(4) R would be the case even though not -P were the case .
(4) is the contrary of (2) , not i t s cont rad ic tory , s ince both (2) and (4) m ay
turn o ut fa l se, n Fo r example , suppos e S as se r ts ,
(2g) I would h ave won the lo t t e ry i f I had bo ugh t two t i cke t s (ins tead
of only one) .
W e m a y de ny t he t r u t h o f th i s c on t e n t i on w i t hou t c om m i t t i ng ou r s e lve s t o
t he t r u t h o f
( 4g ) Y ou w ou l d ha v e l o st e ve n i f you ha d boug h t t w o t i c ket s .
Al l tha t i s in tended in denying (2g) is tha t the pu rchase of two t i cke t s i s con -
nec ted wi th winning in the a l l eged manne r , tha t the purcha se of two t i cke t s
w ou l d ha ve a s s u r e d h i m o f w i nn ing . I t s f a il i ng t o be c onne c t e d i n the
ma nne r a l l eged i s , however , qui t e con s i s t ent wi th his winning with two t i cke t s .
W ha t w e c om m i t ou r s e l ve s t o i n de ny i ng ( 2g ) i s :
(3g) You
might
have los t even wi th two t i cke t s .
(3g) asserts what (2g) denies ; viz. tha t even wi th two t i cke t s i t i s still a m a t t e r
of chance , the poss ib i l i ty of los ing i s not e l i m i na t e d by ho l d i ng t w o t i c ke t s
ins tead of one .
A s a m a t t e r o f c om m o n p r a c t ic e , o f c ou rs e , w e o f t e n e m p l oy s om e t h i ng
s imi la r to (4) in denying (2) . Thi s i s und ers tand able e nou gh s ince the t ru th
o f ( 4~ does enta i l the fa ls i ty of (2) . The po in t I am dr iv ing a t, howev er , is tha t
we need not a f f i rm anyth ing as s t rong as (4) in denying (2) ; a l l we a re requi red
to a f f i rm i s tha t R an d no t -P m i gh t bo t h be t he c a s e o r t ha t , e ve n t hough R
is given, P
might not
be the case . Th a t i s to s ay , the prope r expres s ion for
the neg a t ion o f (2) i s (3) ; and i f we und ers tand (3) as a f f i rming Giv en R ,
( ) -~ P (a l t e rna t ive ly ( ) ( R . ,-~ P) ) , then we a re jus t i f i ed in represe nt ing
(2) as Giv en R , N ( ) ~ p (a l t e rna t ive ly , -,~ ( ) (R . ,-~ P) ) . I f som eon e
s a ys, J a m e s w ou l d no t ha ve c om e w i t hou t a n i nv i t a t i on , w e c a n de ny t h i s
w i t hou t s uppos i ng t ha t J a m e s w ou l d ha ve c om e w i t hou t a n i nv i t a t i on .
F o r s uppos e w e kno w t ha t i f J a m e s h a d no t r e c e ive d a n i nv i ta t i on , he w ou l d
have f l ipped a coin to dec ide whe ther to go or not . In such a case , i t i s no t
t r ue t ha t he w ou l d no t ha ve c om e w i t hou t a n i nv i t a t i on , bu t ne i t he r i s i t
t r ue t ha t he w ou l d ha ve c om e w i t hou t a n i nv i t a ti on . T he f a c t i s t ha t
he
might have come ( de pe nd i ng on t he ou t c om e o f t he t o ss ) w i t hou t a n i nv i t a t ion .
B e f o r e p r oc e e d i ng t he r e i s a n i m por t a n t a m b i gu i t y w h i c h m us t be e l i m i n -
a t e d . T he r e is a u s e o f t he w or d m i gh t ( a nd r e la t e d m o da l t e r m s ) w h i c h
gives expres s ion to the speaker s ep i s t emic s t a t e in re la t ion to some s i tua t ion .
I t is a u s e o f the w or d m i gh t w h i c h i s na t u r a l l y f o ll ow e d by a pa r e n t he t i c a l
f o r al l I kno w . F o r e xa m pl e , i n sa y i ng , H e m i gh t w i n t he el e c t ion t he
11 A point which Go odm an acknowledges in a footn ote: Literally a semifactual and the
corresponding counterfactual are not contradictories hut contraries, and both may be
false. Fa ct Fiction and Forecast p. 32, note 2.
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s pe a ke r is m os t na t u r a l l y unde r s t ood a s e xp r es s ing t he f a c t t ha t he doe s no t
knoW whether he wi l l win the e lec t ion or not , tha t he has n o (or the re a re no)
very convinc ing groun ds for supp os ing he wil l lose . Thi s use of the word ca n
proper ly be deployed even when the s t a t e of a f fa i r s in ques t ion
is physically
o r logically i m pos s i b le . S , f o r i n s ta nc e , m a y c onc e de t he p re m i s e s o f ou r
va l id a rgum ent bu t , none the les s , igno rant o f it s va l id i ty , ins is t tha t the con-
c lus ion might ( for a l l he knows) be fa l se even though the premises a re t rue .
C on t r a s t e d w i t h t h is e p i s t em i c u s e o f the m oda l t e r m s i s w ha t w e m i gh t
cal l an objective s e nse o f t he se t e r m s , a s ens e o f the t e r m c ou l d ( f o r e xa m pl e )
in which i f R enta i l s P then , indepen dent of wha t S know s abo ut the logica l
re la t ionship be tween R a nd P , i t is fa l se to s ay tha t R a nd not -P co uld (or
m i gh t ) bo t h be t he c a se . M or e o ve r , i f w e a c c e p t t he r es u lt s o f m o de r n
phys ics, then in th i s objec t ive sense of the t e rm S s s t a t emen t tha t the re a re
objec t s which can t rave l fas t e r than the speed of l ight is fa lse , and i t i s fa lse
even
though for al l he knows
the re a re objec t s which can . In th i s objec tive
sense one i s making a remark about the va r ious poss ib i l i t i e s for the occur -
rence , or jo in t occur rence , of event s or the co-exi s t ence of s t a t es of a f fa i r s ,
and in th i s s ense ignorance of wha t i s the case i s no g uaran tee th a t o ne s
s t a t e m e n t s a bou t w ha t might o r could be the case a re t rue . The poss ib i l it i e s
m us t a c t ual l y be a s one al le ges . W he n S ( know i ng t ha t J a m e s ha d a n i n -
v i t a t ion to come) as se r t s tha t J am es , be ing the so r t of fe llow he i s, might
( e ve n ) ha ve c om e w i t hou t a n i nv i t a t i on , he i s m a k i ng a r e m a r k
about James
a nd w ha t J a m e s is i ncl ine d t o do o r c a pa b l e o f do i ng . H e i s obv i ous l y no t
r e g is t er i ng s om e f a c t a bou t h i s i gno r a nc e o f w he t he r o r no t J a m e s pos s e s se s
an invi t a t ion .
T he m o da l t e r m a ppe a r i ng i n ( 3 ) i s m e a n t t o be unde r s t oo d i n the ob j e c t ive
sense . (3) i s me an t to be a s t a t em ent ab ou t the possib i l it i e s for the jo in t
r e a li z a ti on o f t w o s t at e s o f af f a ir s ( R a nd no t - P ) i nde pe nde n t o f w ha t t he
s pe a ke r ha ppe n s t o k now a bou t t he a c t ua l r e a li z a t ion o f P ( R be i ng gi ve n) .
D r a w i ng f r om ou r d i s c us s i on i n t he p r e c e d i ng s e c t i on , w e c a n s a y t ha t i f
(2) i s t rue , i f R w ould not be the case unles s P were the case , then
in these
circumstances
(specif ied earl ier) P is a s tate o f affairs whic h is necessar y to
the rea l i za t ion o f R . Hence , in these c i rcums tances i t i s fa l se to s ay tha t
R a nd no t - P m i gh t bo t h be t he c as e o r t ha t , g i ven R , no t - P m i gh t be t he c a se ,
and i t i s fa l se whe ther or no t any one apprec ia te s the fac t tha t i t i s fa lse .
W e ha ve he r e a m o r e o r l e s s
particularized
impossibi l i ty; (3) , as wel l as (2) ,
i s t i ed to the c i rcums tances , C , spec i fi ed ea r l ie r . No thin g e l se but (a s t a t e
such as ) P could h ave bro ugh t ab ou t (a s t a t e such as ) R in these circumstances.
O f t e n , o f c ou r s e , ou r s t a t e m e n t s a bou t w ha t c ou l d be t he c a s e , a bou t w ha t i s
poss ib le , a re broad er in s cope . The y do not res t r i c t themse lves to the
par t i cu la r s e t of c i rcums tances preva i l ing on some spec i f ic occas ion . The y
are s t a t ements to the e f fec t tha t , w ha tever the c i rcum s tances on th i s occas io n
happened to be , the re a re (none the les s ) c i rcums tances in which a s t a t e
re levant ly s imi la r to R i s , or migh t eas ily be , brou ght a bo ut wi th out a s t a t e
r e l e va n tl y s i m i la r to P . S m a y a dm i t , f o r e xa m pl e , t ha t t he t he r m om e t e r
w ou l d no t ha ve r e a d 98 . 6 un l es s t he c h il d s t e m pe r a t u r e w a s no r m a l - - he nc e ,
11
F r e d D r e t s k e
concede tha t i t would be fa lse to say tha t in these c i rcumstances (g iven the
therm omet er reading) the chi ld might (none the less) have a fever . Ye t , he
may go on to ins is t tha t one can ge t a no r m a l r e a d ing on a t he r m om e te r
wi th a feverish chi ld . One can do so when one has a defec t ive the rmom eter ,
when the chi ld is sucking an ice cube , and so on. Th a t i s , one can have
R wi thout P in
o the r
circumsta nces. Thes e general ' possibil i t ies are ,
however , qui te consis tent wi th the 'pa r t icula rized imposs ib i l i tie s expressed
by (3) . Mo st genu ine imposs ib i li t ies can be made poss ib le by enla rging the
f rame of re fe rence , by re laxing the condi t ions tac i t ly taken as f ixed in the
or ig ina l s ta tement o f imposs ib il i ty . I can ' t swim the Engl ish Channe l ;
th is despi te the fac t tha t I co u ld / f I had t ra ined s ince a boy, been endow ed
with the requis i te endu rance , e tc .
I f I may sum mar ize the a rgument u p to th is point in prepara t ion fo r the
fol lowing sec tion: (1) enta i ls (2), i f S knows tha t P , and he knows th is on the
basis (simply) of R, then R would not be the case unless P were the case.
Fur thermore , (2) g ives express ion to a c6nnec t ion be tween R and P which
permits us to say tha t when R is g iven, in the k ind o f ci rcumstances which
ac tua l ly preva i led on the o ccas ion in ques t ion , the poss ib i l i ty of not -P is
e l imina ted . The sense of the word 'poss ib le ' tha t i s opera t ive here i s, I
submit , the s a m e sense of th is word tha t i s opera t ing in our s t ronges t s ta te -
ments abou t wha t i s physica l ly poss ib le; the d i f ference be tween the poss ib i l i ty
expressed in (3) and other , apparent ly s t ronger , s ta tements of wha t i s poss ib le
and impossible is simply a shif t in the set of circumsta nces which is take n as
f ixed. The imposs ib i l ity expressed by (3) is an imposs ib i l i ty re la t ive to tho se
circumstances, C, held f ixed in (2) , and i t is this fact which makes (3) the
contradic tory of (2) and, hence , which makes i t s nega t ion a logica l conse-
quence of (1) .
3 . C onc lus i v e Re aso ns
Let us ca l l R a conc lus ive reason for P i f and only i f R would not be th e
case unless P were th e case. 12 This make s log ically conclusiv e reaso ns
(LCR ) a subclass of conc lus ive reasons . Conc lus ive reasons depend,
s imply , on the t ru th of (2) ; logica l ly conc lus ive reasons require tha t the
t ru th of (2) be demonst rable o n pure ly logical and def in i t iona l grounds .
Wh en the condi t iona l i s t rue , but n ot logica l ly t rue , we can speak of the
conc lus ive reasons as be ing e m p i r i c a l l y c onc lu s i v e (ECR) .
Of c ou rse , R m a y be a conc lus ive reason for be l ieving P wi thout anyone
believing P, much less having R as their reason for believing. I shall say,
the re fore , tha t S has conclusive reasons R, for be l ieving P i f and only i f :
(A) R is a conclusive reaso n for P ( i .e . (2) is true) ,
(B) S be l ieves , wi thout doubt , r ese rva t ion , or ques t ion , tha t P i s the
case and he be l ieves th is on the bas is of R ,
12 Recal l footnote 5 concerning the particular w ording of (2); I intend those remarks to
apply to this definition of 'conclusive reasons'.
12
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8/11/2019 dretske 1971
7/11
Conc lus ive Reasons
( (2 ) ( i ) S kn ow s t ha t R i s t he case o r
( ii ) R i s s o m e e x p e r i m e n t a l s t a te o f S ( a b o u t w h i c h i t m a y n o t
m a k e s e n se to s u p p o s e t h a t S k n o w s t h a t R i s t h e c a s e ; a t
l e a s t i t n o l o n g e r m a k e s m u c h s e n se t o a s k h o w h e k n o w s ) .
W i t h o n l y m i n o r e m b e l l i s h m e n t s , t o b e m e n t i o n e d i n a m o m e n t , I b e li e v e
t h a t S ' s h a v i n g c o n c l u s i v e r e a s o n s f o r b e l i e v i n g P i s both a n e c e s s a r y a n d a
s u ff ic ie n t c o n d i t i o n f o r hi s k n o w i n g t h a t P i s t h e ca s e . T h e a p p e a r a n c e o f
t h e w o r d ' k n o w ' i n t h is c h a r a c t e r i z a t i o n ( i n ( Ci )) d o e s n o t r e n d e r i t c i r c u l a r
a s a c h a r a c t e r i z a t i o n o f k n o w l e d g e s i n c e it c a n b e e l i m i n a t e d b y a r e c u r s i v e
a p p l i c a t i o n o f t h e t h r e e c o n d i t i o n s u n t i l ( C i i) i s r e a c h e d .
I f S h a s c o n c l u s i v e r e a s o n s f o r b e l i e v i n g P , t h e n i t is f a l s e t o s a y t h a t ,
g i ve n t h e s e g r o u n d s f o r b e li e f, a n d t h e c i r c u m s t a n c e s i n w h i c h t h e s e g r o u n d s
s e r v e d a s t h e b a s i s f o r h i s b e l i e f, S m i g h t b e m i s t a k e n a b o u t P . H a v i n g c o n -
c l u s iv e r e a s o n s , a s I h a v e j u s t d e f i n e d i t , n o t o n l y i m p l i e s t h a t P i s t h e c a s e ,
i t n o t o n l y i m p l i e s t h a t S b e l ie v e s t h a t P i s t h e c a s e , b u t i t a l s o i m p l i e s t h a t ,
i n t h e c i r c u m s t a n c e s i n w h i c h h e c a m e t o b e l i e v e t h a t P , h i s b a s i s f o r b e -
l i e vi n g t h a t P w a s s u f f ic i e n t ly s e c u r e t o e l i m i n a t e t h e p o s s i b i l i t y o f h is b e i n g
m i s t a k e n a b o u t P . T h i s g o es a l o n g w a y t o w a r d c a p t u r i n g e v e r y t h i n g t h a t
p h i l o s o p h e r s h a v e tr a d i t i o n a l l y r e q u i r e d o f k n o w l e d g e . I n d e e d , i n c e r t a i n
r e s pe c ts it g o e s b e y o n d i t i n r e q u i r i n g a s t r o n g e r c o n n e c t o n b e t w e e n o n e ' s
r e a s o n s o r g r o u n d s a n d w h a t o n e b e l i ev e s ( o n t h e b a s i s o f th e s e r e a s o n s o r
g r o u n d s ) t h a n h a s n o r m a l l y b e e n d e m a n d e d b y t h o s e w i sh i n g t o p r e s e r v e o u r
o r d i n a r y k n o w l e d g e c l a i m s f r o m s c e p t i c a l c r i t i c i sm , a S i n c e , h o w e v e r , I
h a v e a l r e a d y a r g u e d f o r t h e n e c e s s i t y o f ( A ) , f o r R ' s b e i n g a c o n c l u s i v e
r e a s o n fo r P , I s h a l l c o n c e n t r a t e o n t h e q u e s t i o n o f w h e t h e r o r n o t S ' s h a v i n g
a c o n c l u s i v e r e a s o n f o r b e l i e v i n g P i s s u f f ic i e n t f o r h i s k n o w i n g t h a t P .
13 It is this stronger conn ection which blocks the sort o f counterexample which can be
generated to justified-true-belief analyses of knowledge. Gett ier 's (and Lehrer 's)
examples, for instance, are directed at those analyses which construe knowledge in
terms of a degree of justification which is compatible with being justified in believing
something false (both G ett ier and Leh rer mention this feature at the beginning of their
discussion). The counterexamples are then constructed by allowing S to believe that P
(which is false)
with the appropriate degree o f justification
let t ing P entail Q (which is
true), and let t ing S believe that Q on the basis of i ts logical relat ionship to P. We have,
then, a case where S truly believes that Q with t he appropriate degree o f justification
(this degree of justification is al legedly preserved through the en tailment between P and
Q), but a case where S does not know that Q (since his means of arriving as i t were so
clearly defective). On the present analysis, of course, the required connection between
S's evidence and P is strong enough to preclude P's being false. One cannot have con-
clusive reasons for believing something which is false. Hence, this sort of counter-
example cannot be generated. Part o f the motivation for the present analysis is the
conviction (supported by Gett ier-l ike examples) that knowledge, if i t embod ies an evi-
dential relat ion at al l , must embody a strong enough one to el iminate the possibility
of mistake. See Edmu nd Gett ier 's 'Is Justified True Belief Know ledge? ' Analysis
23.6, June 1963 and Keith Lehrer, 'Knowledge, Truth and Evidence',
Analysis
25.5,
April 1965. I should also mention here that these same sorts of considerations seemed
to mo ve Brian Skyrms tow ard a similar analysis; see especially pp. 385-86 in his 'T he
Explication of X Knows That P ' The Journal of Philosophy June 22, 1967.
2
13
Fred Dretske
Severa l p re l iminary po in ts mus t be ment ioned br ief ly . I t may be thought
that in argu ing fo r the imposs ib i l i ty o f mis take as a necessary condi t ion fo r
knowing tha t P I have been was t ing my t ime. I t ma y be thoug ht tha t i f S
k n o w s t h a t
P, then P cannot be f a l se s ince S s knowing tha t P en ta i l s P ;
hence, S cannot be mis taken in be l iev ing tha t P . In answer to th is ob jec t ion
i t shou ld be po in ted o u t tha t the imposs ib i l i ty o f mis take which I have been
talking ab out is an impossibil i ty which ar ises in vir tue of a special connection
between S s r easons , R, and w hat he conseq uen t ly bel ieves, P. I t is no t the
t r iv ia l imposs ib i l i ty o f be ing wrong about someth ing which (by hypothes is )
you know. Wh en ph i losopher s concern themselves wi th the poss ib i li ty o f
mis take in pu ta t ive cases o f knowledge, they are no t c oncern ed wi th the
poss ib i l i ty o f mis take which i s t r iv ia l ly avo idab le by say ing tha t / fyou do
k n o w t h a t P , t h en y o u can n o t b e m i s tak en ab o u t P . T h ey a r e con ce r n ed ,
r a ther , w i th tha t poss ib i l ity as i t ex is t s in r e la t ion to one s ev idence o r g rounds
for be l iev ing P , an d that is the possibil i ty with which (2) is concerned.
T h e p o i n t m ay b e p u t i n an o t h e r w ay. B o t h
I . R would not be the case unless P were the case
R is the case
an d
II. R ~ P (when it is not t rue tha t R would no t be the case un less P)
cons t i tu te conclus ive g rounds , log ica l ly conclus ive g rounds , fo r be l iev ing P .
Nei ther se t o f premises would be t rue un less P were t rue , a nd th i s f ac t is in
bo th cases demons t r ab le on pure ly log ica l and def in i t ional g rounds . But the
signif icant dif ference between I a nd I I is tha t in I , but not in I I , the second
premise alone tu rns ou t to be a conclusive r eason (ECR) . I f we were search ing
for conclus ive r easons to be l ieve P , then in the second case we would r equ i r e
as our r easons both premises and th i s would r equ i r e tha t we knew that bo th
premises were true (see clause (C) in having conclusive reasons) . In case I ,
however , the second premise a lone i s a conclus ive r eason and , hence , to have
conclus ive r easons i t i s r equ i r ed only tha t we kno w that R is the case. W e
need no t ( as in case II ) know tha t the f i r s t p remise is t rue . A l l tha t i s r e-
qu i r ed in case I fo r R a lone to be a conclus ive r eason is tha t the f i r s t p remise
be t rue ; there i s no th ing th a t r equ i r es S to know that the f i rs t p remise i s t rue
in o rder to have R as h i s conclus ive r eason fo r be l iev ing P . For i f the f i r st
premis e is t rue ( regardless of whe the r S knows i t is t rue or no t) then (3) is
f a l se ; hence , the poss ib i li ty o f S s be ing mis taken abou t P has bee n success -
fu l ly avo ide d- -a nd i t has been success ful ly avo ided whether or not S knows
it has been avoided.
In speak ing o f conclus ive r easons I d o n o t wish to sugges t tha t in hav ing R
as a conclus ive r eason S mus t be in a pos i t ion to give R as his reason. R
ma y s imply be a cer ta in exper ience which S has undergone a nd , hav ing under -
gone th i s exper ience , come to the bel ief tha t P was the case on the bas i s o f
(as a result of) this exper ience. He m ay f ind i t dif ficult , or impossible, to
g ive verbal express ion to R. He ma y have fo rgo t ten R. Or R may cons ist
14
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8/11/2019 dretske 1971
8/11
Conclusive Reasons
i n s o m e t h i n g s l o o k i n g a p a r t i c u l a r w a y t o h i m w h i c h h e f i n d s di f fi c u lt t o
d e s cr ib e . S ti ll , i f t h e w a y t h e t h i n g l o o k s t o S i s s u c h t h a t i t w o u l d n o t l o o k
t h a t w a y u n l es s i t h a d t h e p r o p e r t y Q , t h e n i ts l o o k i n g t h a t w a y t o S is a
c o n c l u si v e r e a s o n f o r S s b e l i ev i n g t h a t i t h a s t h e p r o p e r t y Q ; a n d i f S
bel ieves that i t is Q
on this basis,
t h e n h e h a s , i n t h e w a y t h e t h i n g l o o k s t o
h im, a conc lus ive r eason f or be l iev ing i t Q .
A l s o, t h er e a r e a n u m b e r o f t h i n gs w h i c h p e o p l e c o m m o n l y p r o f e ss t o k n o w
( S a c r a m e n t o i s t h e c a p i t a l o f C a l i f o r n i a , t h e e a r t h i s r o u g h l y s p h e r i c a l ) f o r
w hich the r e i s no de f in i te p iece o f ev idence , no s ing le s ta te o f a f f a i rs o r eas i ly
spec if iab le s e t o f such s ta tes , w hich even app r ox ima tes a conc lus ive r eason .
I n s u c h c a se s , a l t h o u g h w e c a n c i te n o s i ng l e p ie c e o f d a t a w h i c h i s c l i n c h i n g
a n d , h e n c e , a r e a t a l o s s f o r c o n c l u s i v e r e a s o n s w h e n a s k e d t o g i v e r e a s o n s
( o r w h e n a s k e d H o w d o y o u k n o w ? ) w e, n o n et h e le s s, o f t e n e n o u g h h a v e
c o n c l u si v e r e a s o n s i n a v a s t s p e c t r u m o f e x p e ri e n c e s w h i c h a r e t o o d i v e rs e
t o a d m i t o f c o n v e n i e n t c i ta t i o n . C o u n t l e s s e x p e r ie n c e s c o n v e r g e , s o t o s p e ak ,
o n t h e t r u t h o f a g iv e n p r o p o s i t i o n , a n d t h i s v a r i e t y o f ex p e r i e n c e m a y b e
s u ch t h a t a l t h o u g h o n e may h a v e h a d a n y one o f t h e se e x p e r i e n c e s w i t h o u t
t h e p r o p o s i t i o n i n q u e s t i o n b e i n g t r u e , o n e would not h a v e h a d a / / o f t h e m
unles s w h a t one con sequ ent ly be l ieves w as t r ue . The f a l l ib i li ty o f sour ce A
a n d t h e f a l li b i li t y o f s o u r ce B d o e s n o t a u t o m a t i c a l l y e n t a i l t h a t w h e n A a n d
B agree ab ou t P s be ing the case , tha t , none the les s , P mig ht s t i l l be f a l se .
F o r i t m a y b e t h a t A a n d B
would not
b o t h h a v e i n d i c a t e d t h a t P w a s t h e c a s e
u n l es s P w a s t h e c a s e a l t h o u g h n e i t h e r A n o r B , t a k e n b y t h e m s el v e s , p r o v i d e
c o n c l u s iv e r e a s o n s f o r P . F o r e x a m p l e , a l t h o u g h a n y s i n g le n e w s p a p e r
a c c o u n t m a y b e i n e r r o r o n a p a r t i c u l a r p o i n t , s e v er a l i n d e p e n d e n t v e r s i o n s
( w ir e s er v ic e s, o f c o u r s e , t e n d t o e l i m i n a te t h i s i n d e p e n d e n c e ) m a y b e e n o u g h
t o s a y t h a t w e k n o w t h a t s o m e t h i n g i s s o
on the basis of the newspaper accounts.
A l l o f t h e m w o u l d n o t h a v e b e e n i n s u c h c l o s e a g r e e m e n t u n l e s s t h e i r a c c o u n t
w as subs tan t ia l ly cor r ec t . 14
F i n a l l y , I d o n o t w i s h t o s u g g e s t b y m y u se o f t h e w o r d r e a s o n t h a t w h e n
S has conc lus ive r easons f or be l iev ing P , S has reasoned h i s w a y t o t h e c o n -
c l u s i o n t h a t P i s t h e c a s e f r o m p r e m i s e s i n v o l v i n g R o r t h a t S h as c o n s c i o u s l y
u s e d R a s a r e a s o n i n a r r i v i n g a t t h e b e l i e f t h a t P . I a m i n c l i n e d t o t h i n k
( b u t I s h a l l n o t n o w a r g u e i t ) t h a t w h e n o n e k n o w s t h a t P , o n w h a t e v e r b a s i s
t h is m i g h t b e , li t tl e o r n o r e a s o n i n g i s i n v o l v e d . I w o u l d p r e f e r t o d e s c r ib e
i t as f o l l o w s : s o m e t i m e s a p e r s o n s c o n v i c t i o n t h a t P i s th e c a s e c a n b e
t r aced to a s ta te o f af f a ir s ( o r c lus te r o f s i tua t ions ) w hich sa t is f ie s the th r ee
c o n d i t i o n s d e f i n i n g t h e p o s s e s si o n o f c o n c l u s i v e r e a s o n s . W h e n i t c a n b e s o
t r a c e d , t h e n h e k n o w s ; w h e n i t c a n n o t b e s o tr a c e d , t h e n w e s a y h e d o e s n o t
14 The fa ct tha t all newspapers som etimes prin t things w hich are false does no t mean that
we canno t kno w th at something is true on the basis of a single newspaper account.
The relevant question to ask (as in the case of a person s testimon y--see section 1) is not
whether
newspapers
sometimes print false stories, no t even whether
this newspaper
some-
times prints false stories, but whether
this newspaperwould
have printed
this story
if it were
not true. The Midville Weekly Gazette s story about dope addiction on the campus
may not correspond with the facts, but would The Times have printed this story about
the President s visit to Moscow if it were not tru e?
15
Fred Dretske
k n o w a l t h o u g h h e m a y b e r i g h t a b o u t P s b e i n g t h e c as e . O f c o u r se , h is
b e l i e f m a y b e traceable t o such a source wi thout our be ing able to t race i t .
I n s u c h a c a s e w e a r e m i s t a k e n i n s a y i n g t h a t h e d o e s n o t k n o w .
T u r n i n g n o w t o t h e q u e s t i o n o f w h e t h e r h a v i n g c o n c l u s iv e r e a s o n s t o
be l i eve , a s de f ined by (A)- (C) , cons t i tu t es a suf fi c ien t condi t ion for k nowledge ,
I s h a ll m e n t i o n a n d b r i ef l y r e s p o n d t o w h a t I c o n s i d e r t o b e t h e m o s t s e r i o u s
objec t ions to th i s proposa l .
There i s , f i r s t , a t endency to conf la t e knowing tha t P wi th knowing tha t one
k n o w s t h a t P . I f th i s is d o n e t h e n c o n d i t i o n s ( A ) -( C ) w i ll im m e d i a t e l y a p p e a r
insuf f i c i en t s ince they do not desc r ibe S as knowing or having any bas i s for
be l i ev ing tha t R , h i s bas i s for be l i ev ing P , cons t i tu t es an ade qua te bas i s , much
less a conc lus ive bas is , for be l i ev ing P . Even i f one does not go th i s fa r the re
i s s t i l l a t endency to s ay tha t i f S knows tha t P , then S mus t a t l eas t believe
t ha t he knows tha t P i s the case . I f one adop t s th is v iew then , once aga in ,
c o n d i t i o n s ( A ) - ( C ) a p p e a r i n a d e q u a t e s in c e t h e y d o n o t d e s c r ib e ( n o r d o t h e y
enta i l) t ha t S be l i eves he knows th a t P i s the case . I see no reason , however ,
t o a c c e p t ei t h e r o f t h e se c l ai m s . W e n a t u r a l l y e x p e c t o f o n e w h o k n o w s t h a t
P tha t he be l i eve tha t h e knows , jus t a s we expec t of som eon e who i s r id ing a
bicyc le tha t he be l i eve he i s r id ing one , b ut in ne i the r case i s the be l i e f a
necessary a c c o m p a n i m e n t . T h e c o n f u s i o n i s p a r t i a l ly f o st e r e d , I b e l ie v e ,
by a fa i lure to d i s t ingui sh be tween wha t i s impl i ed in knowing tha t P , and
w h a t i s i m p l i e d ( in s o m e s e n se ) b y s o m e o n e s saying h e k n o w s t h a t P . C o n -
s ide r , howe ver , cases in which w e f ree ly asc r ibe know ledge to agent s in which
i t s eems qui t e implau s ib le to as s ign the l eve l of conceptu a l soph i s t i ca t ion
r e q u is i te t o t h e i r b e l ie v i n g s o m e t h i n g a b o u t k n o w l e d g e , b e l ie v i n g s o m e t h i n g
ab ou t the i r ep i s temic re l a t ion to the s t a t e of a f fa i rs in ques t ion . A dog may
k n o w t h a t h i s m a s t e r i s i n t h e r o o m , a n d I ( a t le a s t) w a n t t o s a y th a t h e c a n
know th i s in a s t ra ight forward sense wi thout (neces sa r i ly) posses s ing the
c o n c e p t u a l u n d e r s t a n d i n g w h i c h s e e m s t o b e r e q u ir e d t o s a y o f h i m t h a t h e
be l i eves he kn ows th i s , be l i eves tha t he has go od reasons , or be l i eves anything
abo ut h i s ep i s t emic re l a t ion to the fac t tha t h i s mas te r i s in the r oo m. x5
Y e t , i t s e e m s p e r f e c t ly n a t u r a l t o s a y o f a d o g t h a t i t k n o w s ( s o m e t i m e s ) w h e n
h i s m a s t e r i s i n th e r o o m . A n d t h is i s n o t , l e t m e a d d , s i m p l y a m a t t e r o f th e
d o g s b e i n g r ig h t a b o u t s o m e t h i n g . F o r i f w e k n e w t h a t th e d o g t h o u g h t h i s
m a s t e r w a s i n t h e r o o m o n t h e b a s i s , s a y , o f c e r ta i n s o u n d s a n d s m e ll s ( s o u n d s
and smel l s tha t w ere , genera l ly speaking , a re l i ab le sign of h is mas te r ) wh en
these sound s an d sm el l s were to ta l ly unre la t ed to h i s mas te r s presence in the
r o o m on this occasion w e w o u l d n o t s a y t h e d o g k n e w e v e n i f h e h a p p e n e d
t o b e r i g h t a b o u t h i s m a s t e r s b e i n g in t h e r o o m . I m a g i n e a b l in d d o g s
b e i n g t a k e n i n b y a t h i e f in h i s m a s t e r s c l o th i n g w h i l e t h e m a s t e r l ie s u n -
consc ious in the corner . The do g, t aken in as he is by the th ie f , ce r t a in ly
th inks h i s mas te r is in the room , an d he i s r ight (a l though, of course , he is
15 This seems to be the essence of Arth ur Dan to s argument (against Hintikka) th at S
knows that P does not entail S knows that S knows that P in On Knowing that We
Know , Epistemology: New Essays in the Theory of Knowledge Avrum Stroll (ed.),
1967, pp. 49-51.
16
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8/11/2019 dretske 1971
9/11
Conclusive Reasons
w r o n g a b o u t t h i s m a n s b e i n g h is m a s te r ) . B u t j u s t a s c l e a r l y t h e d o g d o e s n o t
k n o W t h a t h i s m a s t e r i s i n t h e r o o m . W e r e q u i r e c o n c l u s i v e re a s o n s e v e n
i n t h e c a s e o f a n i m a l s . W o u l d t h e d o g h a v e s m e l l e d w h a t h e d i d, a n d h e a r d
w h a t h e d i d , i f h i s m a s t e r w a s n o t i n t h e r o o m ? I f h e
wouM have
o r
might
have t h e n h e d o e s n t k n o w . 16
F u r t h e r m o r e , c o n s i d e r a s c e p t i c w h o t a l k e d h i m s e l f i n t o b e l i e v i n g t h a t h i s
g r o u n d s f o r b e l i e v i n g in a n e x t e r n a l w o r l d w e r e n o t s u f fi c ie n t ly g o o d t o t r u l y
s a y h e knew t h e r e w a s a n e x t e r n a l w o r l d a n d , h e n c e , n o l o n g e r b e l i e v e d ,
p o s i ti v e l y d i s b e l ie v e d , t h a t h e k n e w t h e r e w a s a n e x t e r n a l w o r l d . I t h i n k
t h a t as l o n g as h e c o n t i n u e d t o b e l i e v e ( w i t h o u t d o u b t , r e s e r v a t i o n o r q u e s -
t i on ) t h a t t h e r e w a s a n e x t e r n a l w o r l d , a n d c o n t i n u e d t o b e l i e v e i t o n t h e
s a m e b a s is a s w e d o , h e w o u l d k n o w t h e r e w a s a n e x t e r n a l w o r l d ( a s s u m i n g
h e r e t h a t we k n o w i t ) whatever h e h a p p e n e d t o b e l i ev e a b o u t w h a t h e k n e w . 17
T h e r e m a r k s I h a v e j u s t m a d e a b o u t b e l i e v i n g t h a t o n e k n o w s a p p l y , a
fortiori
t o k n o w i n g t h a t o n e k n o w s . O n e q u a li f ie s f o r k n o w l e d g e w h e n o n e
h a s c o n c l u s i v e r e a s o n s f o r b e l i e v i n g ; o n e n e e d n o t , i n a d d i t i o n , k n o w t h a t
o n e h a s c o n c l u s i v e g r o u n d s . T o k n o w t h a t o n e h a s c o n c l u s i v e r e a s o n s ,
e m p i r i c a ll y c o n c l u s i v e r e a s o n s , m e a n s t h a t o n e k n o w s t h a t ( A ) i s t r u e a n d
t h is , i n t u r n , m e a n s t h a t o n e h a s l o g i c a l l y c o n c l u s i v e r e a s o n s ( s e e c a s e I
a b o v e) . K n o w i n g t h a t o n e k n o w s i s a f o r m o f i n n o c u l a t i o n a g a i n s t s c e p t i c al
c h a l le n g e s to t h e q u a l i t y o f o n e s e m p i r i c a l l y c o n c l u s i v e r e a s o n s ; o n e knows
16 Robert Sleigh has suggested an interesting modification of this cas e--o ne that w ould
appear to cause difficulty. Suppose that the dog is taken in by the th ief but, in addit ion,
circumstances are such that the thief
wouM not
be in the room
unless
the dog s mas te r
was also there. I t m ay be a bit diff icult to imagine circumstances of this sort , but o ther
examples (not involving animals as the knowers) can easily be manufa ctured (Chisholm s
example of a man mistaking a sheep dog for a sheep in a f ield works nicely when the
further condit ion is added that the dog w ould not be there unless there were some sheep
in the f ield). With such a modification it would seem that the dog has conclusive
reasons for believing his master present since i t would not hav e heard and smelled what
i t did unless i ts master was present. But does the dog kno w that i ts master is present ?
I think i t natural to re ad this si tuation in such a way that the d og believes that i ts master
i s in the room because i t mistakenly believes that this man (the thief) is his master . If
read in this way, of course, there is no difficulty since the d og s basis for believing that
his master is present is obviously defective--i t is not true, nor does th e dog know,
that this man is his master . If , however, we read this case in such a way that the do g
simply takes the sounds and smells as a sign of his master s presence (without mis-
identifying anyone) then the dog does have conclusive reasons (he wo uld not h ave
smelled and heard what he did unless his master was presen0 but I should want to say
that in this case he knows that his master is present. I do not think that this is an ex-
cessively strained interpretation. I t seems to me quite similar to si tuations in which we
know that something is so on the basis of some indicator or sign (e.g. an instrument
reading) but are ignorant as to the mechanism in virtue of whichthat indicator o r sign is a
reliable (conclusive) index of what we purport to know.
17 Examples such as this, along with oth er mo re systematic considerations, con vince me
that not only should we not require that S believe he has conclusive reasons in order to
know, but also that we should not re quire that he not believe he does not have con -
clusive reasons. If a person s believing that he knows is compatible with his not know ing,
why shou ldn t a person s believing that he does not k now be compa tible with his
knowing ?
2 .
1 7
Fred Dretske
t ha t R w ould no t be t he ca se un l e ss P we re the case . Lac k ing such innocu-
l a t i on , howeve r , one s t il l know s . One i s s imply l e ss p rep a red t o de fend
(just i fy) the claim t o k n o w l e d g e ; b u t i n a b il i ty t o j us t i f y t h e t r u t h o f w h a t o n e
c l a ims , is se ldom, i f eve r , a r e fu t a t i o n o f t he t ru th o f wha t one c l a ims , and
th i s app l i e s t o knowledge c l a ims a s we l l a s any o the r .
The re i s a c e r t a in t ype o f coun te r -ex ample which exp lo i t s t h i s confus ion ,
and I wou ld l i ke t o men t ion i t a t t h i s po in t t o fu r the r c l a r i fy t he i n t en t o f
cond i t i o ns (A) - (C) . Suppo se S , fo r a pe r fec t l y s i ll y r ea son , o r by shee r
acc iden t , come s t o t he t rue be l i e f t ha t ( a s t a te such a s ) R i s a conc lus ive
rea son fo r be li ev ing tha t ( a s t at e such a s ) P i s o r was t he ca se . Hap pen ing
upon a s t a t e such a s R in t he appropr i a t e c i r cumstances , t hen , he be l i eves t ha t
P i s t h e c a s e o n t h e b as i s o f R . D o e s n ' t h e n o w h a v e
conclusive reasons
f o r
be l i ev ing P ? Bu t i sn ' t i t equa l ly obv io us t ha t he does
not
know tha t P i s t he
case ? Yes and no . Yes , he does hav e conc lus ive rea sons ( a s I have de f ined
th is ) . No , i t i s no t obv io us t ha t he does no t kno w tha t P is t he ca se . I
be l i eve t ha t t h i s ob j ec t i on t r ades on t he ve ry confu s ion we have j us t d i scussed ;
tha t i s , i t m i s t aken ly supp oses t ha t i f S does no t kno w th a t R i s conc lus ive
fo r P (ha s no l eg i t ima te ba s i s fo r be l i ev ing th i s) , t hen S does n o t kno w tha t
P i s t he ca se (ha s no l eg i t ima te ba s i s fo r be l i ev ing thi s ). Or , w ha t I t h ink
amount s t o t he ve ry same th ing , i t f a l l a c ious ly conc ludes t ha t S (g iven h i s
bas i s fo r be l i e f ) m igh t be wrong abou t P f rom the f ac t t ha t S (g iven h i s ba s i s
fo r be li e f ) m igh t be wro ng abo u t R ' s be ing conc lus ive fo r P . Or , t o pu t i t i n
s ti ll ano th e r way , i t i ncor rec t l y suppo ses t h a t i f i t i s, e i t he r whol ly o r i n pa r t ,
a cc iden t a l t ha t S i s r i gh t abou t R ' s be ing conc lus ive fo r P , t hen i t i s a l so ,
e i t he r whol ly o r i n pa r t , a cc iden t a l t ha t he i s r i gh t abou t P ' s be ing t he ca se .
Such inferences are fa l lac ious and, I be l ieve , they are fa l lac ious in the same
w a y a s t h e f o l l o w i n g t w o e x a m p l e s : ( a) C o n c l u d i n g t h a t i t w a s s h e e r l u c k
(chance ) , a me re acc iden t , t ha t dec l a re r m ade h i s b id o f seven spades becau se
i t was shee r l uck ( chance ) , a mere acc iden t , t h a t he was dea l t t h i r t e en spa des ;
( b ) C o n c l u d i n g t h a t t h e w i n d o w w a s b r o k e n a c c i d e n t a l l y b e c a u s e t h e m a n
w h o t h r e w t h e b r i c k t h r o u g h i t c a m e b y t h e b el i ef t h a t b r i c k s b r e a k w i n d o w s
in an acc iden t a l ( s i l l y , un rea sonab le , o r wha t have you) way .
Some t imes t he s t age i s se t fo r a non-acc iden t i n a pure ly acc iden t a l way .
In t he above ca se i t
is
a c c i d en t a l t h a t S k n o w s t h a t P o n t h e b a s is o f R , b u t
t h is d o e s n o t m a k e i t a c c i d en t a l t h a t h e i s r i g h t a b o u t P - - f o r h e b e li ev e s P o n
the ba s i s o f R an d R s im ply wou ld no t be t he case un l ess P we re t he ca se .
Give n R , i t i s no t a t a ll a cc iden t a l t ha t he is r i gh t abou t P . Wh a t is acc iden t a l
i s t ha t he was co r rec t i n be li ev ing t ha t R was a conc lus ive r ea son fo r P , bu t a l l
t h is s h o w s i s t h a t h e d o e s n o t k n o w t h a t R i s c o n c l u si v e f o r P , d o e s n o t k n o w
tha t he know s tha t P . An d wi th t h i s mu ch I am in fu l l ag reement . 18
xs In speaking of 'accidentality in this conn ection I have in mind Peter Unge r's analysis
of knowledge in terms o f its no t being at all accidental th at the perso n is right (see his
'An Analysis of Factual K nowledge'
Journal o f Philosophy
Marc h 21, 1968). Tha t is, I
want to claim that any S satisfying conditions (A)-(C) is a person of whom it is true to
say that it is not at all accidental that he is right about P's being the case, although it
may he accidental that this is no accident (it may be accidental that he
has
conclusive
reasons, that he has reasons in virtue of which it is not at all accidental that he is fight
about P).
18
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8/11/2019 dretske 1971
10/11
C onc l us i ve R easons
Scept ica l a rguments have t r ad i t ional ly r e l ied on the f ac t tha t S , in pur -
por t ing to know that P o n the bas is o f R, was consp icuous ly unab le to
jus t ify the qual i ty o f h is r easons , was hopeless ly incapab le o f p rov id ing
sat i s fac to ry docu men ta t ion fo r the t ru th o f (A) . The co nclus ion fa l lac ious ly
drawn f rom th is was tha t S d id no t know that P was t rue ( s imply) on the
basis o f R. Clear ly , however , a l l tha t fo l lows f rom the f ac t tha t S has l i t t le
or no g rounds fo r th ink ing (A) t rue i s tha t he lacks sa t i s f ac to ry g rounds fo r
th ink ing he knows tha t P is t rue . I t does no t fo l low that he does no t know
that P i s t rue . Know ing tha t P i s the case on the basi s o f R invo lves knowing
that R is the case (and be lieving P o n that basis)
w hen A ) i s t rue .
I t is the
t ru th o f (A) , no t the f ac t tha t o ne knows i t t rue , which makes R conclus ive
for P.
There i s ano t her r espect in which t r ad i t ional scep t ica l a rguments ha ve been
on the mark . One way of express ing my argum ent i s to say tha t the f ami l iar
and ( to some) ex t r emely annoy ing chal lenge, Cou ldn t i t be an i l lusion
( fake , imi ta t ion , e tc . ) ? o r I sn t i t poss ib le tha t you are d reaming (hal luc inat -
ing , e tc . ) ? i s , in a cer ta in impor tan t r espect , qu i te p roper and appropr ia te
even w hen t here i s no spec i a l r eason t o t h i nk you are dreami ng , ha l l uc i na t ing ,
con f ron t i ng a f a ke , e t c .
For our knowledge c la ims do en ta i l tha t the ev i -
dence o r g rounds one has fo r be l iev ing
w o u l d n o t
have been avai lab le i f
what one consequen t ly bel ieves ( and c la ims to know) were f a l se ; hence ,
they do en ta i l tha t , g iven one s ev idence o r g roun ds ,
i t i s f a l s e t ha t one
m i g h t b e m i s t a k e n
abou t what one purpor t s to know. (1 ) does en ta i l the
fa ls i ty o f (3 ) ; hence , (1 ) can be sh own to be f a lse no t on ly by show ing tha t
S is
dreaming or ha l luc inat ing