the critique of pure reason- 第8部分

posteriori；　that　is；　through　experience。　Knowledge　a　priori　is

either　pure　or　impure。　Pure　knowledge　a　priori　is　that　with　which　no

empirical　element　is　mixed　up。　For　example；　the　proposition；　〃Every

change　has　a　cause；〃　is　a　proposition　a　priori；　but　impure；　because

change　is　a　conception　which　can　only　be　derived　from　experience。



　　II。　The　Human　Intellect；　even　in　an　Unphilosophical　State；

　　　　　　is　in　Possession　of　Certain　Cognitions　〃a　priori〃。



　　The　question　now　is　as　to　a　criterion；　by　which　we　may　securely

distinguish　a　pure　from　an　empirical　cognition。　Experience　no　doubt

teaches　us　that　this　or　that　object　is　constituted　in　such　and　such

a　manner；　but　not　that　it　could　not　possibly　exist　otherwise。　Now；

in　the　first　place；　if　we　have　a　proposition　which　contains　the　idea

of　necessity　in　its　very　conception；　it　is　a　if；　moreover；　it　is　not

derived　from　any　other　proposition；　unless　from　one　equally

involving　the　idea　of　necessity；　it　is　absolutely　priori。　Secondly；　an

empirical　judgement　never　exhibits　strict　and　absolute；　but　only

assumed　and　comparative　universality　（by　induction）；　therefore；　the

most　we　can　say　is…　so　far　as　we　have　hitherto　observed；　there　is　no

exception　to　this　or　that　rule。　If；　on　the　other　hand；　a　judgement

carries　with　it　strict　and　absolute　universality；　that　is；　admits　of

no　possible　exception；　it　is　not　derived　from　experience；　but　is　valid

absolutely　a　priori。

　　Empirical　universality　is；　therefore；　only　an　arbitrary　extension　of

validity；　from　that　which　may　be　predicated　of　a　proposition　valid

in　most　cases；　to　that　which　is　asserted　of　a　proposition　which

holds　good　in　all；　as；　for　example；　in　the　affirmation；　〃All　bodies

are　heavy。〃　When；　on　the　contrary；　strict　universality　characterizes　a

judgement；　it　necessarily　indicates　another　peculiar　source　of

knowledge；　namely；　a　faculty　of　cognition　a　priori。　Necessity　and

strict　universality；　therefore；　are　infallible　tests　for

distinguishing　pure　from　empirical　knowledge；　and　are　inseparably

connected　with　each　other。　But　as　in　the　use　of　these　criteria　the

empirical　limitation　is　sometimes　more　easily　detected　than　the

contingency　of　the　judgement；　or　the　unlimited　universality　which　we

attach　to　a　judgement　is　often　a　more　convincing　proof　than　its

necessity；　it　may　be　advisable　to　use　the　criteria　separately；　each

being　by　itself　infallible。

　　Now；　that　in　the　sphere　of　human　cognition　we　have　judgements

which　are　necessary；　and　in　the　strictest　sense　universal；

consequently　pure　a　priori；　it　will　be　an　easy　matter　to　show。　If　we

desire　an　example　from　the　sciences；　we　need　only　take　any　proposition

in　mathematics。　If　we　cast　our　eyes　upon　the　commonest　operations　of

the　understanding；　the　proposition；　〃Every　change　must　have　a

cause；〃　will　amply　serve　our　purpose。　In　the　latter　case；　indeed；

the　conception　of　a　cause　so　plainly　involves　the　conception　of　a

necessity　of　connection　with　an　effect；　and　of　a　strict　universality

of　the　law；　that　the　very　notion　of　a　cause　would　entirely

disappear；　were　we　to　derive　it；　like　Hume；　from　a　frequent

association　of　what　happens　with　that　which　precedes；　and　the　habit

thence　originating　of　connecting　representations…　the　necessity

inherent　in　the　judgement　being　therefore　merely　subjective。

Besides；　without　seeking　for　such　examples　of　principles　existing　a

priori　in　cognition；　we　might　easily　show　that　such　principles　are　the

indispensable　basis　of　the　possibility　of　experience　itself；　and

consequently　prove　their　existence　a　priori。　For　whence　could　our

experience　itself　acquire　certainty；　if　all　the　rules　on　which　it

depends　were　themselves　empirical；　and　consequently　fortuitous？　No

one；　therefore；　can　admit　the　validity　of　the　use　of　such　rules　as

first　principles。　But；　for　the　present；　we　may　content　ourselves

with　having　established　the　fact；　that　we　do　possess　and　exercise　a

faculty　of　pure　a　priori　cognition；　and；　secondly；　with　having　pointed

out　the　proper　tests　of　such　cognition；　namely；　universality　and

necessity。

　　Not　only　in　judgements；　however；　but　even　in　conceptions；　is　an　a

priori　origin　manifest。　For　example；　if　we　take　away　by　degrees　from

our　conceptions　of　a　body　all　that　can　be　referred　to　mere　sensuous

experience…　colour；　hardness　or　softness；　weight；　even

impenetrability…　the　body　will　then　vanish；　but　the　space　which　it

occupied　still　remains；　and　this　it　is　utterly　impossible　to

annihilate　in　thought。　Again；　if　we　take　away；　in　like　manner；　from

our　empirical　conception　of　any　object；　corporeal　or　incorporeal；

all　properties　which　mere　experience　has　taught　us　to　connect　with　it；

still　we　cannot　think　away　those　through　which　we　cogitate　it　as

substance；　or　adhering　to　substance；　although　our　conception　of

substance　is　more　determined　than　that　of　an　object。　Compelled；

therefore；　by　that　necessity　with　which　the　conception　of　substance

forces　itself　upon　us；　we　must　confess　that　it　has　its　seat　in　our

faculty　of　cognition　a　priori。



　　III。　Philosophy　stands　in　need　of　a　Science　which　shall

　　　　　　　Determine　the　Possibility；　Principles；　and　Extent　of

　　　　　　　Human　Knowledge　〃a　priori〃



　　Of　far　more　importance　than　all　that　has　been　above　said；　is　the

consideration　that　certain　of　our　cognitions　rise　completely　above　the

sphere　of　all　possible　experience；　and　by　means　of　conceptions；　to

which　there　exists　in　the　whole　extent　of　experience　no

corresponding　object；　seem　to　extend　the　range　of　our　judgements

beyond　its　bounds。　And　just　in　this　transcendental　or　supersensible

sphere；　where　experience　affords　us　neither　instruction　nor

guidance；　lie　the　investigations　of　reason；　which；　on　account　of　their

importance；　we　consider　far　preferable　to；　and　as　having　a　far　more

elevated　aim　than；　all　that　the　understanding　can　achieve　within　the

sphere　of　sensuous　phenomena。　So　high　a　value　do　we　set　upon　these

investigations；　that　even　at　the　risk　of　error；　we　persist　in

following　them　out；　and　permit　neither　doubt　nor　disregard　nor

indifference　to　restrain　us　from　the　pursuit。　These　unavoidable

problems　of　mere　pure　reason　are　God；　freedom　（of　will）；　and

immortality。　The　science　which；　with　all　its　preliminaries；　has　for

its　especial　object　the　solution　of　these　problems　is　named

metaphysics…　a　science　which　is　at　the　very　outset　dogmatical；　that

is；　it　confidently　takes　upon　itself　the　execution　of　this　task

without　any　previous　investigation　of　the　ability　or　inability　of

reason　for　such　an　undertaking。

　　Now　the　safe　ground　of　experience　being　thus　abandoned；　it　seems

nevertheless　natural　that　we　should　hesitate　to　erect　a　building

with　the　cognitions　we　possess；　without　knowing　whence　they　come；

and　on　the　strength　of　principles；　the　origin　of　which　is

undiscovered。　Instead　of　thus　trying　to　build　without　a　foundation；　it

is　rather　to　be　expected　that　we　should　long　ago　have　put　the

question；　how　the　understanding　can　arrive　at　these　a　priori

cognitions；　and　what　is　the　extent；　validity；　and　worth　which　they　may

possess？　We　say；　〃This　is　natural　enough；〃　meaning　by　the　word

natural；　that　which　is　consistent　with　a　just　and　reasonable　way　of

thinking；　but　if　we　understand　by　the　term；　that。　which　usually

happens；　nothing　indeed　could　be　more　natural　and　more

comprehensible　than　that　this　investigation　should　be　left　long

unattempted。　For　one　part　of　our　pure　knowledge；　the　science　of

mathematics；　has　been　long　firmly　established；　and　thus　leads　us　to

form　flattering　expectations　with　regard　to　others；　though　these　may

be　of　quite　a　different　nature。　Besides；　when　we　get　beyond　the　bounds

of　experience；　we　are　of　course　safe　from　opposition　in　that

quarter；　and　the　charm　of　widening　the　range　of　our　knowledge　is　so

great　that；　unless　we　are　brought　to　a　standstill　by　some　evident

contradiction；　we　hurry　on　undoubtingly　in　our　course。　This；

however；　may　be　avoided；　if　we　are　sufficiently　cautious　in　the

construction　of　our　fictions；　which　are　not　the　less　fictions　on

that　account。

　　Mathematical　science　affords　us　a　brilliant　example；　how　far；

independently　of　all　experience；　we　may　carry　our　a　priori

knowledge。　It　is　true　that　the　mathematician　occupies　himself　with

objects　and　cognitions　only　in　so　far　as　they　can　be　represented　by

means　of　intuition。　But　this　circumstance　is　easily　overlooked；

because　the　said　intuition　can　itself　be　given　a　priori；　and　therefore

is　hardly　to　be　distinguished　from　a　mere　pure　conception。　Deceived　by

such　a　proof　of　the　power　of　reason；　we　can　perceive　no　limits　to

the　extension　of　our　knowledge。　The　light　dove　cleaving　in　free　flight

the　thin　air；　whose　resistance　it　feels；　might　imagine　that　her

movements　would　be　far　more　free　and　rapid　in　airless　space。　just　in

the　same　way　did　Plato；　abandoning　the　world　of　sense　because　of　the

narrow　limits　it　sets　to　the　understanding；　venture　upon　the　wings

of　ideas　beyond　it；　into　the　void　space　of　pure　intellect。　He　did

not　reflect　that　he　made　no　real　progress　by　all　his　efforts；　for　he

met　with　no　resistance　which　might　serve　him　for　a　support；　as　it

were；　whereon　to　rest；　and　on　which　he　might　apply　his　powers；　in

order　to　let　the　intellect　acquire　momentum　for　its　progress。　It　is；

indeed；　the　common　fate　of　human　reason　in　speculation；　to　finish

the　imposing　edifice　of　thought　as　rapidly　as　possible；　and　then　for

the　first　time　to　begin　to　examine　whether　the　foundation　is　a　solid

one　or　no。　Arrived　at　this　point；　all　sorts　of　excuses　are　sought

after；　in　order　to　console　us　for　its　want　of　stability；　or　rather；

indeed；　to　enable　Us　to　dispense　altogether　with　so　late　and　dangerous

an　investigation。　But　what　frees　us　during　the　process　of　building

from　all　apprehension　or　suspicion；　and　flatters　us　into　the　belief　of

its　solidity；　is　this。　A　great　part；　perhaps　the　greatest　part；　of　the

business　of　our　reason　consists　in　the　analysation　of　the

c