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　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
  window…sill；　and　the　shoemarks　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　on　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
  kinds　of　marks　have　not　been　left　by　any　other　animals　than　men；　or　are
  liable　to　be　formed　in　any　other　way　than　by　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