the critique of pure reason- 第3部分

within　the　province　of　pure　reason　advances　with　that　undeviating

certainty　which　characterizes　the　progress　of　science；　we　shall　be

at　no　loss　to　determine。　If　we　find　those　who　are　engaged　in

metaphysical　pursuits；　unable　to　come　to　an　understanding　as　to　the

method　which　they　ought　to　follow；　if　we　find　them；　after　the　most

elaborate　preparations；　invariably　brought　to　a　stand　before　the

goal　is　reached；　and　compelled　to　retrace　their　steps　and　strike

into　fresh　paths；　we　may　then　feel　quite　sure　that　they　are　far　from

having　attained　to　the　certainty　of　scientific　progress　and　may　rather

be　said　to　be　merely　groping　about　in　the　dark。　In　these　circumstances

we　shall　render　an　important　service　to　reason　if　we　succeed　in　simply

indicating　the　path　along　which　it　must　travel；　in　order　to　arrive

at　any　results…　even　if　it　should　be　found　necessary　to　abandon　many

of　those　aims　which；　without　reflection；　have　been　proposed　for　its

attainment。

　　That　logic　has　advanced　in　this　sure　course；　even　from　the

earliest　times；　is　apparent　from　the　fact　that；　since　Aristotle；　it

has　been　unable　to　advance　a　step　and；　thus；　to　all　appearance　has

reached　its　completion。　For；　if　some　of　the　moderns　have　thought　to

enlarge　its　domain　by　introducing　psychological　discussions　on　the

mental　faculties；　such　as　imagination　and　wit；　metaphysical；

discussions　on　the　origin　of　knowledge　and　the　different　kinds　of

certitude；　according　to　the　difference　of　the　objects　（idealism；

scepticism；　and　so　on）；　or　anthropological　discussions　on

prejudices；　their　causes　and　remedies：　this　attempt；　on　the　part　of

these　authors；　only　shows　their　ignorance　of　the　peculiar　nature　of

logical　science。　We　do　not　enlarge　but　disfigure　the　sciences　when

we　lose　sight　of　their　respective　limits　and　allow　them　to　run　into

one　another。　Now　logic　is　enclosed　within　limits　which　admit　of

perfectly　clear　definition；　it　is　a　science　which　has　for　its　object

nothing　but　the　exposition　and　proof　of　the　formal　laws　of　all

thought；　whether　it　be　a　priori　or　empirical；　whatever　be　its　origin

or　its　object；　and　whatever　the　difficulties…　natural　or　accidental…

which　it　encounters　in　the　human　mind。

　　The　early　success　of　logic　must　be　attributed　exclusively　to　the

narrowness　of　its　field；　in　which　abstraction　may；　or　rather　must；

be　made　of　all　the　objects　of　cognition　with　their　characteristic

distinctions；　and　in　which　the　understanding　has　only　to　deal　with

itself　and　with　its　own　forms。　It　is；　obviously；　a　much　more　difficult

task　for　reason　to　strike　into　the　sure　path　of　science；　where　it

has　to　deal　not　simply　with　itself；　but　with　objects　external　to

itself。　Hence；　logic　is　properly　only　a　propaedeutic…　forms；　as　it

were；　the　vestibule　of　the　sciences；　and　while　it　is　necessary　to

enable　us　to　form　a　correct　judgement　with　regard　to　the　various

branches　of　knowledge；　still　the　acquisition　of　real；　substantive

knowledge　is　to　be　sought　only　in　the　sciences　properly　so　called；

that　is；　in　the　objective　sciences。

　　Now　these　sciences；　if　they　can　be　termed　rational　at　all；　must

contain　elements　of　a　priori　cognition；　and　this　cognition　may　stand

in　a　twofold　relation　to　its　object。　Either　it　may　have　to　determine

the　conception　of　the　object…　which　must　be　supplied　extraneously；

or　it　may　have　to　establish　its　reality。　The　former　is　theoretical；

the　latter　practical；　rational　cognition。　In　both；　the　pure　or　a

priori　element　must　be　treated　first；　and　must　be　carefully

distinguished　from　that　which　is　supplied　from　other　sources。　Any

other　method　can　only　lead　to　irremediable　confusion。

　　Mathematics　and　physics　are　the　two　theoretical　sciences　which

have　to　determine　their　objects　a　priori。　The　former　is　purely　a

priori；　the　latter　is　partially　so；　but　is　also　dependent　on　other

sources　of　cognition。

　　In　the　earliest　times　of　which　history　affords　us　any　record；

mathematics　had　already　entered　on　the　sure　course　of　science；　among

that　wonderful　nation；　the　Greeks。　Still　it　is　not　to　be　supposed　that

it　was　as　easy　for　this　science　to　strike　into；　or　rather　to　construct

for　itself；　that　royal　road；　as　it　was　for　logic；　in　which　reason

has　only　to　deal　with　itself。　On　the　contrary；　I　believe　that　it

must　have　remained　long…　chiefly　among　the　Egyptians…　in　the　stage

of　blind　groping　after　its　true　aims　and　destination；　and　that　it

was　revolutionized　by　the　happy　idea　of　one　man；　who　struck　out　and

determined　for　all　time　the　path　which　this　science　must　follow；　and

which　admits　of　an　indefinite　advancement。　The　history　of　this

intellectual　revolution…　much　more　important　in　its　results　than　the

discovery　of　the　passage　round　the　celebrated　Cape　of　Good　Hope…　and

of　its　author；　has　not　been　preserved。　But　Diogenes　Laertius；　in

naming　the　supposed　discoverer　of　some　of　the　simplest　elements　of

geometrical　demonstration…　elements　which；　according　to　the　ordinary

opinion；　do　not　even　require　to　be　proved…　makes　it　apparent　that

the　change　introduced　by　the　first　indication　of　this　new　path；　must

have　seemed　of　the　utmost　importance　to　the　mathematicians　of　that

age；　and　it　has　thus　been　secured　against　the　chance　of　oblivion。　A

new　light　must　have　flashed　on　the　mind　of　the　first　man　（Thales；　or

whatever　may　have　been　his　name）　who　demonstrated　the　properties　of

the　isosceles　triangle。　For　he　found　that　it　was　not　sufficient　to

meditate　on　the　figure；　as　it　lay　before　his　eyes；　or　the　conception

of　it；　as　it　existed　in　his　mind；　and　thus　endeavour　to　get　at　the

knowledge　of　its　properties；　but　that　it　was　necessary　to　produce

these　properties；　as　it　were；　by　a　positive　a　priori　construction；　and

that；　in　order　to　arrive　with　certainty　at　a　priori　cognition；　he　must

not　attribute　to　the　object　any　other　properties　than　those　which

necessarily　followed　from　that　which　he　had　himself；　in　accordance

with　his　conception；　placed　in　the　object。

　　A　much　longer　period　elapsed　before　physics　entered　on　the　highway

of　science。　For　it　is　only　about　a　century　and　a　half　since　the　wise

Bacon　gave　a　new　direction　to　physical　studies；　or　rather…　as　others

were　already　on　the　right　track…　imparted　fresh　vigour　to　the

pursuit　of　this　new　direction。　Here；　too；　as　in　the　case　of

mathematics；　we　find　evidence　of　a　rapid　intellectual　revolution。　In

the　remarks　which　follow　I　shall　confine　myself　to　the　empirical

side　of　natural　science。

　　When　Galilei　experimented　with　balls　of　a　definite　weight　on　the

inclined　plane；　when　Torricelli　caused　the　air　to　sustain　a　weight

which　he　had　calculated　beforehand　to　be　equal　to　that　of　a　definite

column　of　water；　or　when　Stahl；　at　a　later　period；　converted　metals

into　lime；　and　reconverted　lime　into　metal；　by　the　addition　and

subtraction　of　certain　elements；*　a　light　broke　upon　all　natural

philosophers。　They　learned　that　reason　only　perceives　that　which　it

produces　after　its　own　design；　that　it　must　not　be　content　to

follow；　as　it　were；　in　the　leading…strings　of　nature；　but　must　proceed

in　advance　with　principles　of　judgement　according　to　unvarying　laws；

and　compel　nature　to　reply　its　questions。　For　accidental　observations；

made　according　to　no　preconceived　plan；　cannot　be　united　under　a

necessary　law。　But　it　is　this　that　reason　seeks　for　and　requires。　It

is　only　the　principles　of　reason　which　can　give　to　concordant

phenomena　the　validity　of　laws；　and　it　is　only　when　experiment　is

directed　by　these　rational　principles　that　it　can　have　any　real

utility。　Reason　must　approach　nature　with　the　view；　indeed；　of

receiving　information　from　it；　not；　however；　in　the　character　of　a

pupil；　who　listens　to　all　that　his　master　chooses　to　tell　him；　but

in　that　of　a　judge；　who　compels　the　witnesses　to　reply　to　those

questions　which　he　himself　thinks　fit　to　propose。　To　this　single

idea　must　the　revolution　be　ascribed；　by　which；　after　groping　in　the

dark　for　so　many　centuries；　natural　science　was　at　length　conducted

into　the　path　of　certain　progress。



　　*I　do　not　here　follow　with　exactness　the　history　of　the　experimental

method；　of　which；　indeed；　the　first　steps　are　involved　in　some

obscurity。



　　We　come　now　to　metaphysics；　a　purely　speculative　science；　which

occupies　a　completely　isolated　position　and　is　entirely　independent　of

the　teachings　of　experience。　It　deals　with　mere　conceptions…　not；　like

mathematics；　with　conceptions　applied　to　intuition…　and　in　it；

reason　is　the　pupil　of　itself　alone。　It　is　the　oldest　of　the　sciences；

and　would　still　survive；　even　if　all　the　rest　were　swallowed　up　in　the

abyss　of　an　all…destroying　barbarism。　But　it　has　not　yet　had　the

good　fortune　to　attain　to　the　sure　scientific　method。　This　will　be

apparent；　if　we　apply　the　tests　which　we　proposed　at　the　outset。　We

find　that　reason　perpetually　comes　to　a　stand；　when　it　attempts　to

gain　a　priori　the　perception　even　of　those　laws　which　the　most

common　experience　confirms。　We　find　it　compelled　to　retrace　i