the origination of living beings-第2章

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science　work　by　means　of　Induction　and　Deduction；　and　that　by　the　help
of　these　operations；　they；　in　a　sort　of　sense；　wring　from　Nature
certain　other　things；　which　are　called　Natural　Laws；　and　Causes；　and
that　out　of　these；　by　some　cunning　skill　of　their　own；　they　build　up
Hypotheses　and　Theories。　　And　it　is　imagined　by　many；　that　the
operations　of　the　common　mind　can　be　by　no　means　compared　with　these
processes；　and　that　they　have　to　be　acquired　by　a　sort　of　special
apprenticeship　to　the　craft。　To　hear　all　these　large　words；　you　would
think　that　the　mind　of　a　man　of　science　must　be　constituted　differently
from　that　of　his　fellow　men；　but　if　you　will　not　be　frightened　by
terms；　you　will　discover　that　you　are　quite　wrong；　and　that　all　these
terrible　apparatus　are　being　used　by　yourselves　every　day　and　every
hour　of　your　lives。

There　is　a　well…known　incident　in　one　of　Moliere's　plays；　where　the
author　makes　the　hero　express　unbounded　delight　on　being　told　that　he
had　been　talking　prose　during　the　whole　of　his　life。　　In　the　same　way；
I　trust；　that　you　will　take　comfort；　and　be　delighted　with　yourselves；
on　the　discovery　that　you　have　been　acting　on　the　principles　of
inductive　and　deductive　philosophy　during　the　same　period。　　Probably
there　is　not　one　here　who　has　not　in　the　course　of　the　day　had　occasion
to　set　in　motion　a　complex　train　of　reasoning；　of　the　very　same　kind；
though　differing　of　course　in　degree；　as　that　which　a　scientific　man
goes　through　in　tracing　the　causes　of　natural　phenomena。

A　very　trivial　circumstance　will　serve　to　exemplify　this。　　Suppose　you
go　into　a　fruiterer's　shop；　wanting　an　apple；you　take　up　one；　and；　on
biting　it；　you　find　it　is　sour；　you　look　at　it；　and　see　that　it　is　hard
and　green。　　You　take　up　another　one；　and　that　too　is　hard；　green；　and
sour。　　The　shopman　offers　you　a　third；　but；　before　biting　it；　you
examine　it；　and　find　that　it　is　hard　and　green；　and　you　immediately　say
that　you　will　not　have　it；　as　it　must　be　sour；　like　those　that　you　have
already　tried。

Nothing　can　be　more　simple　than　that；　you　think；　but　if　you　will　take
the　trouble　to　analyze　and　trace　out　into　its　logical　elements　what　has
been　done　by　the　mind；　you　will　be　greatly　surprised。　　In　the　first
place；　you　have　performed　the　operation　of　Induction。　　You　found　that；
in　two　experiences；　hardness　and　greenness　in　apples　go　together　with
sourness。　　It　was　so　in　the　first　case；　and　it　was　confirmed　by　the
second。　　True；　it　is　a　very　small　basis；　but　still　it　is　enough　to　make
an　induction　from；　you　generalize　the　facts；　and　you　expect　to　find
sourness　in　apples　where　you　get　hardness　and　greenness。　　You　found
upon　that　a　general　law；　that　all　hard　and　green　apples　are　sour；　and
that；　so　far　as　it　goes；　is　a　perfect　induction。　Well；　　having　got　your
natural　law　in　this　way；　when　you　are　offered　another　apple　which　you
find　is　hard　and　green；　you　say；　〃All　hard　and　green　apples　are　sour；
this　apple　is　hard　and　green；　therefore　this　apple　is　sour。〃　　That
train　of　reasoning　is　what　logicians　call　a　syllogism；　and　has　all　its
various　parts　and　terms；its　major　premiss；　its　minor　premiss；　and　its
conclusion。　　And；　by　the　help　of　further　reasoning；　which；　if　drawn
out；　would　have　to　be　exhibited　in　two　or　three　other　syllogisms；　you
arrive　at　your　final　determination；　〃I　will　not　have　that　apple。〃　　So
that；　you　see；　you　have；　in　the　first　place；　established　a　law　by
Induction；　and　upon　that　you　have　founded　a　Deduction；　and　reasoned　out
the　special　conclusion　of　the　particular　case。　　Well　now；　suppose；
having　got　your　law；　that　at　some　time　afterwards；　you　are　discussing
the　qualities　of　apples　with　a　friend：　you　will　say　to　him；　〃It　is　a
very　curious　thing；but　I　find　that　all　hard　and　green　apples　are
sour！〃　　Your　friend　says　to　you；　〃But　how　do　you　know　that？〃　You　at
once　reply；　〃Oh；　because　I　have　tried　it　over　and　over　again；　and　have
always　found　them　to　be　so。〃　　Well。　if　we　were　talking　science　instead
of　common　sense；　we　should　call　that　an　Experimental　Verification。　And；
if　still　opposed；　you　go　further；　and　say；　〃I　have　heard　from　the
people　in　Somersetshire　and　Devonshire；　where　a　large　number　of　apples
are　grown；　that　they　have　observed　the　same　thing。　　It　is　also　found　to
be　the　case　in　Normandy；　and　in　North　America。　　In　short；　I　find　it　to
be　the　universal　experience　of　mankind　wherever　attention　has　been
directed　to　the　subject。〃　　Whereupon；　your　friend；　unless　he　is　a　very
unreasonable　man；　agrees　with　you；　and　is　convinced　that　you　are　quite
right　in　the　conclusion　you　have　drawn。　　He　believes；　although　perhaps
he　does　not　know　he　believes　it；　that　the　more　extensive　Verifications
are；that　the　more　frequently　experiments　have　been　made；　and　results
of　the　same　kind　arrived　at；that　the　more　varied　the　conditions　under
which　the　same　results　have　been　attained；　the　more　certain　is　the
ultimate　conclusion；　and　he　disputes　the　question　no　further。　　He　sees
that　the　experiment　has　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　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　parlour　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
minutes　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　what　you　have　said　has　been　the　expression　of
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