autobiography and selected essays-第26章

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been　tried　under　all　sorts　of　conditions；　as　to　time；　place；　and

people；　with　the　same　result；　and　he　says　with　you；　therefore；　that

the　law　you　have　laid　down　must　be　a　good　one；　and　he　must　believe

it。



In　science　we　do　the　same　thing；the　philosopher　exercises

precisely　the　same　faculties；　though　in　a　much　more　delicate

manner。　　In　scientific　inquiry　it　becomes　a　matter　of　duty　to

expose　a　supposed　law　to　every　possible　kind　of　verification；　and

to　take　care；　moreover；　that　this　is　done　intentionally；　and　not

left　to　a　mere　accident；　as　in　the　case　of　the　apples。　　And　in

science；　as　in　common　life；　our　confidence　in　a　law　is　in　exact

proportion　to　the　absence　of　variation　in　the　result　of　our

experimental　verifications。　　For　instance；　if　you　let　go　your　grasp

of　an　article　you　may　have　in　your　hand；　it　will　immediately　fall

to　the　ground。　　That　is　a　very　common　verification　of　one　of　the

best　established　laws　of　naturethat　of　gravitation。　　The　method

by　which　men　of　science　establish　the　existence　of　that　law　is

exactly　the　same　as　that　by　which　we　have　established　the　trivial

proposition　about　the　sourness　of　hard　and　green　apples。　　But　we

believe　it　in　such　an　extensive；　thorough；　and　unhesitating　manner

because　the　universal　experience　of　mankind　verifies　it；　and　we　can

verify　it　ourselves　at　any　time；　and　that　is　the　strongest　possible

foundation　on　which　any　natural　law　can　rest。



So　much；　then；　by　way　of　proof　that　the　method　of　establishing　laws

in　science　is　exactly　the　same　as　that　pursued　in　common　life。　　Let

us　now　turn　to　another　matter　（though　really　it　is　but　another

phase　of　the　same　question）；　and　that　is；　the　method　by　which；　from

the　relations　of　certain　phenomena；　we　prove　that　some　stand　in　the

position　of　causes　towards　the　others。



I　want　to　put　the　case　clearly　before　you；　and　I　will　therefore

show　you　what　I　mean　by　another　familiar　example。　　I　will　suppose

that　one　of　you；　on　coming　down　in　the　morning　to　the　parlor　of

your　house；　finds　that　a　tea…pot　and　some　spoons　which　had　been

left　in　the　room　on　the　previous　evening　are　gone；the　window　is

open；　and　you　observe　the　mark　of　a　dirty　hand　on　the　window…frame；

and　perhaps；　in　addition　to　that；　you　notice　the　impress　of　a　hob…

nailed　shoe　on　the　gravel　outside。　　All　these　phenomena　have　struck

your　attention　instantly；　and　before　two　seconds　have　passed　you

say；　〃Oh；　somebody　has　broken　open　the　window；　entered　the　room；

and　run　off　with　the　spoons　and　the　tea…pot！〃　　That　speech　is　out

of　your　mouth　in　a　moment。　　And　you　will　probably　add；　〃I　know

there　has；　I　am　quite　sure　of　it！〃　　You　mean　to　say　exactly　what

you　know；　but　in　reality　you　are　giving　expression　to　what　is；　in

all　essential　particulars；　an　hypothesis。　　You　do　not　KNOW　it　at

all；　it　is　nothing　but　an　hypothesis　rapidly　framed　in　your　own

mind。　　And　it　is　an　hypothesis　founded　on　a　long　train　of

inductions　and　deductions。



What　are　those　inductions　and　deductions；　and　how　have　you　got　at

this　hypothesis？　　You　have　observed　in　the　first　place；　that　the

window　is　open；　but　by　a　train　of　reasoning　involving　many

inductions　and　deductions；　you　have　probably　arrived　long　before　at

the　general　lawand　a　very　good　one　it　isthat　windows　do　not

open　of　themselves；　and　you　therefore　conclude　that　something　has

opened　the　window。　　A　second　general　law　that　you　have　arrived　at

in　the　same　way　is；　that　tea…pots　and　spoons　do　not　go　out　of　a

window　spontaneously；　and　you　are　satisfied　that；　as　they　are　not

now　where　you　left　them；　they　have　been　removed。　　In　the　third

place；　you　look　at　the　marks　on　the　windowsill；　and　the　shoe…marks

outside；　and　you　say　that　in　all　previous　experience　the　former

kind　of　mark　has　never　been　produced　by　anything　else　but　the　hand

of　a　human　being；　and　the　same　experience　shows　that　no　other

animal　but　man　at　present　wears　shoes　with　hob…nails　in　them　such

as　would　produce　the　marks　in　the　gravel。　　I　do　not　know；　even　if

we　could　discover　any　of　those　〃missing　links〃　that　are　talked

about；　that　they　would　help　us　to　any　other　conclusion！　　At　any

rate　the　law　which　states　our　present　experience　is　strong　enough

for　my　present　purpose。　　You　next　reach　the　conclusion　that；　as

these　kind　＇89＇　of　marks　have　not　been　left　by　any　other　animal　than

man；　or　are　liable　to　be　formed　in　any　other　way　than　a　man's　hand

and　shoe；　the　marks　in　question　have　been　formed　by　a　man　in　that

way。　　You　have；　further；　a　general　law；　founded　on　observation　and

experience；　and　that；　too；　is；　I　am　sorry　to　say；　a　very　universal

and　unimpeachable　one；that　some　men　are　thieves；　and　you　assume

at　once　from　all　these　premissesand　that　is　what　constitutes　your

hypothesisthat　the　man　who　made　the　marks　outside　and　on　the

window…sill；　opened　the　window；　got　into　the　room；　and　stole　your

tea…pot　and　spoons。　　You　have　now　arrived　at　a　vera　causa；you

have　assumed　a　cause　which；　it　is　plain；　is　competent　to　produce

all　the　phenomena　you　have　observed。　　You　can　explain　all　these

phenomena　only　by　the　hypothesis　of　a　thief。　　But　that　is　a

hypothetical　conclusion；　of　the　justice　of　which　you　have　no

absolute　proof　at　all；　it　is　only　rendered　highly　probable　by　a

series　of　inductive　and　deductive　reasonings。



I　suppose　your　first　action；　assuming　that　you　are　a　man　of

ordinary　common　sense；　and　that　you　have　established　this

hypothesis　to　your　own　satisfaction；　will　very　likely　be　to　go　off

for　the　police；　and　set　them　on　the　track　of　the　burglar；　with　the

view　to　the　recovery　of　your　property。　　But　just　as　you　are

starting　with　this　object；　some　person　comes　in；　and　on　learning

what　you　are　about；　says；　〃My　good　friend；　you　are　going　on　a　great

deal　too　fast。　　How　do　you　know　that　the　man　who　really　made　the

marks　took　the　spoons？　　It　might　have　been　a　monkey　that　took　them；

and　the　man　may　have　merely　looked　in　afterwards。〃　　You　would

probably　reply；　〃Well；　that　is　all　very　well；　but　you　see　it　is

contrary　to　all　experience　of　the　way　tea…pots　and　spoons　are

abstracted；　so　that；　at　any　rate；　your　hypothesis　is　less　probable

than　mine。〃　　While　you　are　talking　the　thing　over　in　this　way；

another　friend　arrives；　one　of　the　good　kind　of　people　that　I　was

talking　of　a　little　while　ago。　　And　he　might　say；　〃Oh；　my　dear　sir；

you　are　certainly　going　on　a　great　deal　too　fast。　　You　are　most

presumptuous。　　You　admit　that　all　these　occurrences　took　place　when

you　were　fast　asleep；　at　a　time　when　you　could　not　possibly　have

known　anything　about　what　was　taking　place。　　How　do　you　know　that

the　laws　of　Nature　are　not　suspended　during　the　night？　　It　may　be

that　there　has　been　some　kind　of　supernatural　interference　in　this

case。〃　　In　point　of　fact；　he　declares　that　your　hypothesis　is　one

of　which　you　cannot　at　all　demonstrate　the　truth；　and　that　you　are

by　no　means　sure　that　the　laws　of　Nature　are　the　same　when　you　are

asleep　as　when　you　are　awake。



Well；　now；　you　cannot　at　the　moment　answer　that　kind　of　reasoning。

You　feel　that　your　worthy　friend　has　you　somewhat　at　a

disadvantage。　　You　will　feel　perfectly　convinced　in　your　own　mind；

however；　that　you　are　quite　right；　and　you　say　to　him；　〃My　good

friend；　I　can　only　be　guided　by　the　natural　probabilities　of　the

case；　and　if　you　will　be　kind　enough　to　stand　aside　and　permit　me

to　pass；　I　will　go　and　fetch　the　police。〃　　Well；　we　will　suppose

that　your　journey　is　successful；　and　that　by　good　luck　you　meet

with　a　policeman；　that　eventually　the　burglar　is　found　with　your

property　on　his　person；　and　the　marks　correspond　to　his　hand　and　to

his　boots。　　Probably　any　jury　would　consider　those　facts　a　very

good　experimental　verification　of　your　hypothesis；　touching　the

cause　of　the　abnormal　phenomena　observed　in　your　parlor；　and　would

act　accordingly。



Now；　in　this　supposititious　case；　I　have　taken　phenomena　of　a　very

common　kind；　in　order　that　you　might　see　what　are　the　different

steps　in　an　ordinary　pr