dretske, fred. conclusive reasons

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  • 8/23/2019 Dretske, Fred. Conclusive Reasons

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    This article was downloaded by:[University of Toronto][University of Toronto]

    On: 11 May 2007Access Details: [subscription number 769429897]Publisher:RoutledgeInforma Ltd Registered in England and Wales Registered Number: 1072954Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3J H, UK

    Australasian J ournal of PhilosophyPublication details, including instructions for authors and subscription information:http://www.informaworld.com/smpp/title~content=t713659165

    Conclusive reasonsFred Dretske

    a

    aUniversity of Wisconsin.

    To cite this Article: Fred Dretske , 'Conclusive reasons ', Australasian J ournal ofPhilosophy, 49:1, 1 - 22To link to this article: DOI: 10.1080/00048407112341001URL: http://dx.doi.org/10.1080/00048407112341001

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    Australasian Journa l of PhilosophyVol. 49, No. 1; May, 1971

    F R E D D R E r S K EC O N C L U S I V E R E A S O N S *

    C o n c l u s i v e r e a s o n s h a v e a m o d a l a s w e l l a s a n e p i s te m i c c h a r a c t e r . I nh a v i n g c o n c l u s i v e r e a s o n s t o b e l ie v e t h a t P is th e c a s e o n e ' s e p i s te m i c c r e d e n -t ia ls a r e su c h a s t o e li m i n a t e t h e p o s s i b i l i t y o f m i s t a k e . T h i s , a t le a s t, ish 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 i s p a p e r . L e t t in gt h e s y m b o l ' ( ) ' r e p r e s e n t t h e 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 if ie d s en s eo f poss ib i l i t y ) , I s h a ll s a y , t h e n , t h a t R is a c o n c l u s i v e r e a s o n f o r P i f a n do n l y i f, g i v e n R , ~ ( ) ,-~ P ( o r , a l t e r n a t i v e l y , ~ ( ) ( R . ~ P ) ) . T h i s i n t e r -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 j ec t , S , w h o b e l ie v e s t h a t P a n d w h o h a sc o n c l u s iv e r e a s o n s f o r b e li e v in g t h a t P , t h a t , g i v e n t h e s e r e a s o n s , h e c o u Mn o t b e w r o n g a b o u t P o r , g i v e n t h e s e re a s o n s , i t i s f a l s e t h a t h e m ig h t b em i s ta k e n a b o u t P .

    S u p p o s e , t h e n , t h a t( I ) S k n o w s t h a t P a n d h e k n o w s t h is o n t h e b a si s (s i m p l y ) o f R e n ta i ls( 2) R w o u l d n o t b e t h e c a s e u n l e s s P w e r e t h e c a s e . 1

    T h e l a t t e r f o r m u l a e x p r e ss e s a c o n n e c t i o n b e t w e e n R a n d P w h i c h is s t r o n ge n o u g h , I s u b m i t , t o p e r m i t u s t o s a y t h a t i f ( 2 ) is t r u e , t h e n R i s a c o n c l u s i v er e a s o n f o r P . F o r i f ( 2) is t r u e , w e a r e e n t i tl e d, n o t o n l y t o d e n y th a t , g i v e n R ,n o t - P is t h e c a s e , b u t a l so t h a t , g i v e n R , n o t - P m i g h t b e t h e c a s e . T h a t is t os a y , ( 2 ) e l i m i n a t e s R a n d n o t - P a s a p o s s i b l e ( jo i n t ) s t a t e o f a f f a ir s a n d , w h e nw e a r e g iv e n R , i t e l i m i n a t e s n o t - P a s a p o s s i b l e s t a t e o f a f f ai rs . T h i s is s ob e c a u s e ( 2 ) e n t a i l s t h e f a l s i t y o f ,

    ( 3) A l t h o u g h R is t h e c a s e P m i g h t n o t b e t h e c a s e .I f w e e x p r e s s ( 3 ) a s ' G i v e n R , ( ) ,-~ P ' , t h e n ( 2) e n t a i l s t h a t i t is f a l se t h a t ,g i v e n R , ( ) ~ P w h i c h is e q u i v a l e n t t o , g i v e n R , ~ ( ) ~ P ; a n d th i s isp r e c is e ly t h e r e q u i r e d f e a t u r e o f c o n c l u s i v e r e a s o n s g i v e n a b o v e . H e n c e ,w h e n ( 2 ) is t r u e , R i s a c o n c l u s i v e r e a s o n f o r P .

    W h a t f o l l o w s is a n a m p l i f i c a t i 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 tf o r th e v i e w t h a t i n th o s e c a s e s w h e r e k n o w l e d g e t h a t P r e st s o n e v i d e n c e ,

    *An ear ly vers ion of th is pa per was read to the Ph i losophy D epar tm ent a t T he Uni -versi ty of I ll inois, Ch icago Circle. M ore recently i t was read at T he U niversi ty o f N or thCarol ina 's Col loquium in Phi losophy with Professor Robert Sleigh commenting.x I shal l be using 'R ' and 'P ' to replace a variety o f related g ram ma tical uni ts . De pend ingon the sentential context, they sometimes serve as noun phrases, sometimes as fullindicat ive sentences, sometimes fo r appro priate t ransform ations o f the indicative.

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    F r e d D r e t s k eg r o u n d s , o r r e a s o n s , w h e n t h e q u e s t i o n ' H o w d o e s S k n o w ? ' c a n s e n s i b l yb e a s k e d a n d a n s w e r e d , t h e e v i d e n ce , g r o u n d s , o r r e a s o n s m u s t b e c o n c l u si v e .A n y t h i n g s h o r t o f co n c lu s iv e r e a s o ns , t h o u g h i t m a y p r o v i d e o n e w i t hj u s t if i e d t r u e b e l i ef s , f a il s t o g i v e t h e k i n d o f s u p p o r t r e q u i s i t e t o k n o w l e d g e .I s h a l l a l s o u r g e t h a t t h e p o s s e s s i o n o f c o n c l u s i v e r e a s o n s t o b e l i e v e , p r o p e r l yq u a l i fi e d , is a l so a s u f fi c ie n t c o n d i t i o n f o r k n o w l e d g e .1. K n o w i n g P o n t h e B a s i s o f R : T h e C o n n e c t io n B e t w e e n (1 ) a n d (2) .

    S u p p o s e S , in o r d e r t o a s s ur e h i m s e l f t h a t h is c h i ld ' s t e m p e r a t u r e i sn o r m a l ( n o f e v e r ) , p l a ce s a t h e r m o m e t e r i n t h e c h i l d 's m o u t h , e x t r a c t s ita f t e r se v e ra l m i n u t e s , a n d o b s e r v e s a r e a d i n g o f 9 8.6 F . I n r e m a r k i n g t o t h ed o c t o r t h a t h i s c h i l d ' s t e m p e r a t u r e i s n o r m a l S i s a s k e d h o w h e k n o w s .S r e s p o n d s , n a t u r a l l y e n o u g h , b y s a y in g , ' I j u s t t o o k h is t e m p e r a t u r e ' .L e t u s a s s u m e , t h e n , t h a t w e h a v e a n i n s t a n t i a t i o n o f ( 1 ):

    ( l a ) S k n o w s t h a t h i s c h i l d ' s t e m p e r a t u r e i s n o r m a l a n d h e k n o w s t h i so n t h e b as is o f t h e ( n o r m a l ) r e a d in g o n t h e t h e r m o m e t e r (w h i c hh e h a s j u s t p l a c e d i n t h e c h i l d ' s m o u t h , e tc .) .C a n o n e c o n s i s t e n t ly a f fi rm ( l a ) a n d d e n y th e c o r r e s p o n d i n g i n s ta n t i a t i o n o f( 2 ) ? ( 2 a) T h e t h e r m o m e t e r w o u l d n o t h a v e r e a d 9 8 .6 u n l es s t h e c h i l d 'st e m p e r a t u r e w a s n o r m a l .I f it i s n o t a l r e a d y o b v i o u s t h a t o n e c a n n o t c o n s i s t e n tl y a ff ir m ( l a ) a n d d e n y( 2 a) , I t h i n k i t c a n b e m a d e o b v i o u s b y c o n s i d e r in g th e k i n d o f t h in g w h i c hw o u l d s h o w ( 2a ) t o b e fa ls e. F o r e x a m p l e , i f C h a r l es , f a m i l i a r w i t h t h ep a r t i c u l a r t h e r m o m e t e r in q u e s t i o n , s h o u l d s a y , ' O h , I k n o w t h a t t h e r -m o m e t e r ; i t i s f a i r ly a c c u r a t e f o r t e m p e r a t u r e s b e l o w 9 8 b u t i t s ti ck s a t9 8 .6 f o r a l m o s t a n y h i g h e r t e m p e r a t u r e , ' w e h a v e b e e n g i v en s o li d g r o u n d s f o rr e j ec t in g ( 2 a) . S i m u l t a n e o u s l y , h o w e v e r , w e h a v e b e e n g i v en s o l id g r o u n d sf o r re j e c t in g ( l a ) . I f i t is t h a t k i n d o f t h e r m o m e t e r , t h e n i f S 's o n l y b a si s f o rt h i n k i n g h i s c h i ld ' s t e m p e r a t u r e n o r m a l i s a 98 .6 r e a d i n g o n i t , t h e n h e d o e sn o t k n o w t h a t hi s c h i ld ' s t e m p e r a t u