the critique of pure reason-第151章

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conclusions；　not　from　conceptions；　but　from　intuition　corresponding　to

a　conception；　be　it　pure　intuition；　as　in　mathematics；　or　empirical；

as　in　natural　science；　the　intuition　which　forms　the　basis　of　my

inferences　presents　me　with　materials　for　many　synthetical

propositions；　which　I　can　connect　in　various　modes；　while；　as　it　is

allowable　to　proceed　from　different　points　in　the　intention；　I　can

arrive　by　different　paths　at　the　same　proposition。

　　But　every　transcendental　proposition　sets　out　from　a　conception；　and

posits　the　synthetical　condition　of　the　possibility　of　an　object

according　to　this　conception。　There　must；　therefore；　be　but　one　ground

of　proof；　because　it　is　the　conception　alone　which　determines　the

object；　and　thus　the　proof　cannot　contain　anything　more　than　the

determination　of　the　object　according　to　the　conception。　In　our

Transcendental　Analytic；　for　example；　we　inferred　the　principle：　Every

event　has　a　cause；　from　the　only　condition　of　the　objective

possibility　of　our　conception　of　an　event。　This　is　that　an　event

cannot　be　determined　in　time；　and　consequently　cannot　form　a　part　of

experience；　unless　it　stands　under　this　dynamical　law。　This　is　the

only　possible　ground　of　proof；　for　our　conception　of　an　event

possesses　objective　validity；　that　is；　is　a　true　conception；　only

because　the　law　of　causality　determines　an　object　to　which　it　can

refer。　Other　arguments　in　support　of　this　principle　have　been

attempted…　such　as　that　from　the　contingent　nature　of　a　phenomenon；

but　when　this　argument　is　considered；　we　can　discover　no　criterion

of　contingency；　except　the　fact　of　an　event…　of　something　happening；

that　is　to　say；　the　existence　which　is　preceded　by　the　non…existence

of　an　object；　and　thus　we　fall　back　on　the　very　thing　to　be　proved。　If

the　proposition：　〃Every　thinking　being　is　simple；〃　is　to　be　proved；　we

keep　to　the　conception　of　the　ego；　which　is　simple；　and　to　which　all

thought　has　a　relation。　The　same　is　the　case　with　the　transcendental

proof　of　the　existence　of　a　Deity；　which　is　based　solely　upon　the

harmony　and　reciprocal　fitness　of　the　conceptions　of　an　ens

realissimum　and　a　necessary　being；　and　cannot　be　attempted　in　any

other　manner。

　　This　caution　serves　to　simplify　very　much　the　criticism　of　all

propositions　of　reason。　When　reason　employs　conceptions　alone；　only

one　proof　of　its　thesis　is　possible；　if　any。　When；　therefore；　the

dogmatist　advances　with　ten　arguments　in　favour　of　a　proposition；　we

may　be　sure　that　not　one　of　them　is　conclusive。　For　if　he　possessed

one　which　proved　the　proposition　he　brings　forward　to　demonstration…

as　must　always　be　the　case　with　the　propositions　of　pure　reason…

what　need　is　there　for　any　more？　His　intention　can　only　be　similar

to　that　of　the　advocate　who　had　different　arguments　for　different

judges；　this　availing　himself　of　the　weakness　of　those　who　examine　his

arguments；　who；　without　going　into　any　profound　investigation；　adopt

the　view　of　the　case　which　seems　most　probable　at　first　sight　and

decide　according　to　it。

　　The　third　rule　for　the　guidance　of　pure　reason　in　the　conduct　of　a

proof　is　that　all　transcendental　proofs　must　never　be　apagogic　or

indirect；　but　always　ostensive　or　direct。　The　direct　or　ostensive

proof　not　only　establishes　the　truth　of　the　proposition　to　be

proved；　but　exposes　the　grounds　of　its　truth；　the　apagogic；　on　the

other　hand；　may　assure　us　of　the　truth　of　the　proposition；　but　it

cannot　enable　us　to　comprehend　the　grounds　of　its　possibility。　The

latter　is；　accordingly；　rather　an　auxiliary　to　an　argument；　than　a

strictly　philosophical　and　rational　mode　of　procedure。　In　one　respect；

however；　they　have　an　advantage　over　direct　proofs；　from　the　fact　that

the　mode　of　arguing　by　contradiction；　which　they　employ；　renders　our

understanding　of　the　question　more　clear；　and　approximates　the　proof

to　the　certainty　of　an　intuitional　demonstration。

　　The　true　reason　why　indirect　proofs　are　employed　in　different

sciences　is　this。　When　the　grounds　upon　which　we　seek　to　base　a

cognition　are　too　various　or　too　profound；　we　try　whether　or　not　we

may　not　discover　the　truth　of　our　cognition　from　its　consequences。　The

modus　ponens　of　reasoning　from　the　truth　of　its　inferences　to　the

truth　of　a　proposition　would　be　admissible　if　all　the　inferences

that　can　be　drawn　from　it　are　known　to　be　true；　for　in　this　case　there

can　be　only　one　possible　ground　for　these　inferences；　and　that　is

the　true　one。　But　this　is　a　quite　impracticable　procedure；　as　it

surpasses　all　our　powers　to　discover　all　the　possible　inferences

that　can　be　drawn　from　a　proposition。　But　this　mode　of　reasoning　is

employed；　under　favour；　when　we　wish　to　prove　the　truth　of　an

hypothesis；　in　which　case　we　admit　the　truth　of　the　conclusion…

which　is　supported　by　analogy…　that；　if　all　the　inferences　we　have

drawn　and　examined　agree　with　the　proposition　assumed；　all　other

possible　inferences　will　also　agree　with　it。　But；　in　this　way；　an

hypothesis　can　never　be　established　as　a　demonstrated　truth。　The　modus

tollens　of　reasoning　from　known　inferences　to　the　unknown　proposition；

is　not　only　a　rigorous；　but　a　very　easy　mode　of　proof。　For；　if　it

can　be　shown　that　but　one　inference　from　a　proposition　is　false；

then　the　proposition　must　itself　be　false。　Instead；　then；　of

examining；　in　an　ostensive　argument；　the　whole　series　of　the　grounds

on　which　the　truth　of　a　proposition　rests；　we　need　only　take　the

opposite　of　this　proposition；　and　if　one　inference　from　it　be　false；

then　must　the　opposite　be　itself　false；　and；　consequently；　the

proposition　which　we　wished　to　prove　must　be　true。

　　The　apagogic　method　of　proof　is　admissible　only　in　those　sciences

where　it　is　impossible　to　mistake　a　subjective　representation　for　an

objective　cognition。　Where　this　is　possible；　it　is　plain　that　the

opposite　of　a　given　proposition　may　contradict　merely　the　subjective

conditions　of　thought；　and　not　the　objective　cognition；　or　it　may

happen　that　both　propositions　contradict　each　other　only　under　a

subjective　condition；　which　is　incorrectly　considered　to　be　objective；

and；　as　the　condition　is　itself　false；　both　propositions　may　be　false；

and　it　will；　consequently；　be　impossible　to　conclude　the　truth　of

the　one　from　the　falseness　of　the　other。

　　In　mathematics　such　subreptions　are　impossible；　and　it　is　in　this

science；　accordingly；　that　the　indirect　mode　of　proof　has　its　true

place。　In　the　science　of　nature；　where　all　assertion　is　based　upon

empirical　intuition；　such　subreptions　may　be　guarded　against　by　the

repeated　comparison　of　observations；　but　this　mode　of　proof　is　of

little　value　in　this　sphere　of　knowledge。　But　the　transcendental

efforts　of　pure　reason　are　all　made　in　the　sphere　of　the　subjective；

which　is　the　real　medium　of　all　dialectical　illusion；　and　thus

reason　endeavours；　in　its　premisses；　to　impose　upon　us　subjective

representations　for　objective　cognitions。　In　the　transcendental　sphere

of　pure　reason；　then；　and　in　the　case　of　synthetical　propositions；

it　is　inadmissible　to　support　a　statement　by　disproving　the

counter…statement。　For　only　two　cases　are　possible；　either；　the

counter…statement　is　nothing　but　the　enouncement　of　the

inconsistency　of　the　opposite　opinion　with　the　subjective　conditions

of　reason；　which　does　not　affect　the　real　case　（for　example；　we　cannot

comprehend　the　unconditioned　necessity　of　the　existence　of　a　being；

and　hence　every　speculative　proof　of　the　existence　of　such　a　being

must　be　opposed　on　subjective　grounds；　while　the　possibility　of　this

being　in　itself　cannot　with　justice　be　denied）；　or；　both　propositions；

being　dialectical　in　their　nature；　are　based　upon　an　impossible

conception。　In　this　latter　case　the　rule　applies：　non　entis　nulla　sunt

predicata；　that　is　to　say；　what　we　affirm　and　what　we　deny；　respecting

such　an　object；　are　equally　untrue；　and　the　apagogic　mode　of

arriving　at　the　truth　is　in　this　case　impossible。　If；　for　example；

we　presup