posterior analytics-第13章

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is　the　same；　the　two　opinions　have　objects　so　far　the　same：　on　the



other　hand；　as　regards　their　essential　definable　nature　these



objects　differ。　The　identity　of　the　objects　of　knowledge　and　opinion



is　similar。　Knowledge　is　the　apprehension　of；　e。g。　the　attribute



'animal'　as　incapable　of　being　otherwise；　opinion　the　apprehension



of　'animal'　as　capable　of　being　otherwise…e。g。　the　apprehension　that



animal　is　an　element　in　the　essential　nature　of　man　is　knowledge；



the　apprehension　of　animal　as　predicable　of　man　but　not　as　an



element　in　man's　essential　nature　is　opinion：　man　is　the　subject　in



both　judgements；　but　the　mode　of　inherence　differs。



　　This　also　shows　that　one　cannot　opine　and　know　the　same　thing



simultaneously；　for　then　one　would　apprehend　the　same　thing　as　both



capable　and　incapable　of　being　otherwise…an　impossibility。　Knowledge



and　opinion　of　the　same　thing　can　co…exist　in　two　different　people



in　the　sense　we　have　explained；　but　not　simultaneously　in　the　same



person。　That　would　involve　a　man's　simultaneously　apprehending；　e。g。



（1）　that　man　is　essentially　animal…i。e。　cannot　be　other　than



animal…and　（2）　that　man　is　not　essentially　animal；　that　is；　we　may



assume；　may　be　other　than　animal。



　　Further　consideration　of　modes　of　thinking　and　their　distribution



under　the　heads　of　discursive　thought；　intuition；　science；　art；



practical　wisdom；　and　metaphysical　thinking；　belongs　rather　partly



to　natural　science；　partly　to　moral　philosophy。







　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　34







　　Quick　wit　is　a　faculty　of　hitting　upon　the　middle　term



instantaneously。　It　would　be　exemplified　by　a　man　who　saw　that　the



moon　has　her　bright　side　always　turned　towards　the　sun；　and　quickly



grasped　the　cause　of　this；　namely　that　she　borrows　her　light　from　him；



or　observed　somebody　in　conversation　with　a　man　of　wealth　and



divined　that　he　was　borrowing　money；　or　that　the　friendship　of　these



people　sprang　from　a　common　enmity。　In　all　these　instances　he　has　seen



the　major　and　minor　terms　and　then　grasped　the　causes；　the　middle



terms。



　　Let　A　represent　'bright　side　turned　sunward'；　B　'lighted　from　the



sun'；　C　the　moon。　Then　B；　'lighted　from　the　sun'　is　predicable　of　C；



the　moon；　and　A；　'having　her　bright　side　towards　the　source　of　her



light'；　is　predicable　of　B。　So　A　is　predicable　of　C　through　B。











　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　Book　II



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　　THE　kinds　of　question　we　ask　are　as　many　as　the　kinds　of　things



which　we　know。　They　are　in　fact　four：…（1）　whether　the　connexion　of



an　attribute　with　a　thing　is　a　fact；　（2）　what　is　the　reason　of　the



connexion；　（3）　whether　a　thing　exists；　（4）　What　is　the　nature　of　the



thing。　Thus；　when　our　question　concerns　a　complex　of　thing　and



attribute　and　we　ask　whether　the　thing　is　thus　or　otherwise



qualified…whether；　e。g。　the　sun　suffers　eclipse　or　not…then　we　are



asking　as　to　the　fact　of　a　connexion。　That　our　inquiry　ceases　with　the



discovery　that　the　sun　does　suffer　eclipse　is　an　indication　of　this；



and　if　we　know　from　the　start　that　the　sun　suffers　eclipse；　we　do



not　inquire　whether　it　does　so　or　not。　On　the　other　hand；　when　we　know



the　fact　we　ask　the　reason；　as；　for　example；　when　we　know　that　the　sun



is　being　eclipsed　and　that　an　earthquake　is　in　progress；　it　is　the



reason　of　eclipse　or　earthquake　into　which　we　inquire。



　　Where　a　complex　is　concerned；　then；　those　are　the　two　questions　we



ask；　but　for　some　objects　of　inquiry　we　have　a　different　kind　of



question　to　ask；　such　as　whether　there　is　or　is　not　a　centaur　or　a



God。　（By　'is　or　is　not'　I　mean　'is　or　is　not；　without　further



qualification'；　as　opposed　to　'is　or　is　not　＇e。g。＇　white'。）　On　the



other　hand；　when　we　have　ascertained　the　thing's　existence；　we　inquire



as　to　its　nature；　asking；　for　instance；　'what；　then；　is　God？'　or　'what



is　man？'。







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　　These；　then；　are　the　four　kinds　of　question　we　ask；　and　it　is　in　the



answers　to　these　questions　that　our　knowledge　consists。



　　Now　when　we　ask　whether　a　connexion　is　a　fact；　or　whether　a　thing



without　qualification　is；　we　are　really　asking　whether　the　connexion



or　the　thing　has　a　'middle'；　and　when　we　have　ascertained　either



that　the　connexion　is　a　fact　or　that　the　thing　is…i。e。　ascertained



either　the　partial　or　the　unqualified　being　of　the　thing…and　are



proceeding　to　ask　the　reason　of　the　connexion　or　the　nature　of　the



thing；　then　we　are　asking　what　the　'middle'　is。



　　（By　distinguishing　the　fact　of　the　connexion　and　the　existence　of



the　thing　as　respectively　the　partial　and　the　unqualified　being　of　the



thing；　I　mean　that　if　we　ask　'does　the　moon　suffer　eclipse？'；　or　'does



the　moon　wax？'；　the　question　concerns　a　part　of　the　thing's　being；　for



what　we　are　asking　in　such　questions　is　whether　a　thing　is　this　or



that；　i。e。　has　or　has　not　this　or　that　attribute：　whereas；　if　we　ask



whether　the　moon　or　night　exists；　the　question　concerns　the



unqualified　being　of　a　thing。）



　　We　conclude　that　in　all　our　inquiries　we　are　asking　either　whether



there　is　a　'middle'　or　what　the　'middle'　is：　for　the　'middle'　here



is　precisely　the　cause；　and　it　is　the　cause　that　we　seek　in　all　our



inquiries。　Thus；　'Does　the　moon　suffer　eclipse？'　means　'Is　there　or　is



there　not　a　cause　producing　eclipse　of　the　moon？'；　and　when　we　have



learnt　that　there　is；　our　next　question　is；　'What；　then；　is　this



cause？　for　the　cause　through　which　a　thing　is…not　is　this　or　that；



i。e。　has　this　or　that　attribute；　but　without　qualification　is…and



the　cause　through　which　it　is…not　is　without　qualification；　but　is



this　or　that　as　having　some　essential　attribute　or　some　accident…are



both　alike　the　middle'。　By　that　which　is　without　qualification　I



mean　the　subject；　e。g。　moon　or　earth　or　sun　or　triangle；　by　that　which



a　subject　is　（in　the　partial　sense）　I　mean　a　property；　e。g。　eclipse；



equality　or　inequality；　interposition　or　non…interposition。　For　in　all



these　examples　it　is　clear　that　the　nature　of　the　thing　and　the　reason



of　the　fact　are　identical：　the　question　'What　is　eclipse？'　and　its



answer　'The　privation　of　the　moon's　light　by　the　interposition　of



the　earth'　are　identical　with　the　question　'What　is　the　reason　of



eclipse？'　or　'Why　does　the　moon　suffer　eclipse？'　and　the　reply



'Because　of　the　failure　of　light　through　the　earth's　shutting　it　out'。



Again；　for　'What　is　a　concord？　A　commensurate　numerical　ratio　of　a



high　and　a　low　note'；　we　may　substitute　'What　ratio　makes　a　high　and　a



low　note　concordant？　Their　relation　according　to　a　commensurate



numerical　ratio。'　'Are　the　high　and　the　low　note　concordant？'　is



equivalent　to　'Is　their　ratio　commensurate？'；　and　when　we　find　that　it



is　commensurate；　we　ask　'What；　then；　is　their　ratio？'。



　　Cases　in　which　the　'middle'　is　sensible　show　that　the　object　of



our　inquiry　is　always　the　'middle'：　we　inquire；　because　we　have　not



perceived　it；　whether　there　is　or　is　not　a　'middle'　causing；　e。g。　an



eclipse。　On　the　other　hand；　if　we　were　on　the　moon　we　should　not　be



inquiring　either　as　to　the　fact　or　the　reason；　but　both　fact　and



reason　would　be　obvious　simultaneously。　For　the　act　of　perception



would　have　enabled　us　to　know　the　universal　too；　since；　the　present



fact　of　an　eclipse　being　evident；　perception　would　then　at　the　same



time　give　us　the　present　fact　of　the　earth's　screening　the　sun's



light；　and　from　this　would　arise　the　universal。



　　Thus；　as　we　maintain；　to　know　a　thing's　nature　is　to　know　the　reason



why　it　is；　and　this　is　equally　true　of　things　in　so　far　as　they　are



said　without　qualification　to　he　as　opposed　to　being　possessed　of　some



attribute；　and　in　so　far　as　they　are　said　to　be　possessed　of　some



attribute　such　as　equal　to　right　angles；　or　greater　or　less。







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　　It　is　clear；　then；　that　all　questions　are　a　search　for　a　'middle'。



Let　us　now　state　how　essential　nature　is　revealed　and　in　what　way　it



can　be　reduced　to　demonstration；　what　definition　is；　and　what　things



are　definable。　And　let　us　first　discuss　certain　difficulties　which



these　questions　raise；　beginning　what　we　have　to　say　with　a　point　most



intimately　connected　with　our　immediately　preceding　remarks；　namely



the　doubt　that　might　be　felt　as　to　whether　or　not　it　is　possible　to



know　the　same　thing　in　the　same　relation；　both　by　definition　and　by



demonstration。　It　might；　I　mean；　be　urged　that　definition　is　held　to



concern　essential　nature　and　is　in　every　case　universal　and



affirmative；　whereas；　on　the　other　hand；　some　conclusions　are　negative



and　some　are　not　universal；　e。g。　all　in　the　second　figure　are



negative；　none　in　the　third　are　universal。　And　again；　not　even　all



affirmative　conclusions　in　the　first　figure　are　definable；　e。g。　'every



triangle　has　its　angles　equal　to　two　right　angles'。　An　argument



proving　this　difference　between　demonstration　and　definition　is　that



to　have　scientific　knowledge　of　the　demonstrable　is　identical　with



possessing　a　demonstration　of　it：　hence　if　demonstration　of　such



conclusions　as　these　is　possible；　there　clearly　cannot　also　be



definition　of　them。　If　there　could；　one　might　know　such　a　conclusion



also　in　virtue　of　its　definition　without　possessing　the



demonstration　of　it；　for　there　is　nothing　to　stop　our　having　the　one



without　the　other。



　　Induction　too　will　sufficiently　convince　us　of　this　difference；



for　never　yet　by　defining　anything…essential　attribute　or　accident…did



we　get　knowledge　of　it。　Again；　if　to　define　is　to　acquire　knowledge　of



a　substance；　at　any　rate　such　attributes　are　not　substances。



　　It　is　evident；　then；　that　not　everything　demonstrable　can　be





defined。　What　then？　Can　everything　definable　be　demonstrated；　or



not？　There　is　one　of　our　previous　arguments　which　covers　this　too。



Of　a　single　thing　qua　single　there　is　a　single　scientific　knowledge。



Hence；　since　to　know　the　demonstrable　scientifically　is　to　possess　the



demonstration　of　it；　an　impossible　consequence　will　follow：…possession



of　its　definition　without　its　demonstration　will　give　knowledge　of　the



demonstrable。



　　Moreover；　the　basic　premisses　of　demonstrations　are　definitions；　and



it　has　already　been　shown　that　these　will　be　found　indemonstrable；



either　the　basic　premisses　will　be　demonstrable　and　will　depend　on



prior　premisses；　and　the　regress　will