deciduous。　Thus；　let　D　be　broad…leaved；　E　deciduous；　F　vine。　Then　E
  inheres　in　F　（since　every　vine　is　deciduous）；　and　D　in　E　（for　every
  deciduous　plant　has　broad　leaves）：　therefore　every　vine　has　broad
  leaves；　and　the　cause　is　its　deciduous　character。　If；　however；　they
  cannot　each　be　the　cause　of　the　other　（for　cause　is　prior　to　effect；
  and　the　earth's　interposition　is　the　cause　of　the　moon's　eclipse　and
  not　the　eclipse　of　the　interposition）…if；　then；　demonstration
  through　the　cause　is　of　the　reasoned　fact　and　demonstration　not
  through　the　cause　is　of　the　bare　fact；　one　who　knows　it　through　the
  eclipse　knows　the　fact　of　the　earth's　interposition　but　not　the
  reasoned　fact。　Moreover；　that　the　eclipse　is　not　the　cause　of　the
  interposition；　but　the　interposition　of　the　eclipse；　is　obvious
  because　the　interposition　is　an　element　in　the　definition　of
  eclipse；　which　shows　that　the　eclipse　is　known　through　the
  interposition　and　not　vice　versa。
  On　the　other　hand；　can　a　single　effect　have　more　than　one　cause？　One
  might　argue　as　follows：　if　the　same　attribute　is　predicable　of　more
  than　one　thing　as　its　primary　subject；　let　B　be　a　primary　subject　in
  which　A　inheres；　and　C　another　primary　subject　of　A；　and　D　and　E
  primary　subjects　of　B　and　C　respectively。　A　will　then　inhere　in　D
  and　E；　and　B　will　be　the　cause　of　A's　inherence　in　D；　C　of　A's
  inherence　in　E。　The　presence　of　the　cause　thus　necessitates　that　of
  the　effect；　but　the　presence　of　the　effect　necessitates　the　presence
  not　of　all　that　may　cause　it　but　only　of　a　cause　which　yet　need　not　be
  the　whole　cause。　We　may；　however；　suggest　that　if　the　connexion　to
  be　proved　is　always　universal　and　commensurate；　not　only　will　the
  cause　be　a　whole　but　also　the　effect　will　be　universal　and
  commensurate。　For　instance；　deciduous　character　will　belong
  exclusively　to　a　subject　which　is　a　whole；　and；　if　this　whole　has
  species；　universally　and　commensurately　to　those　species…i。e。　either
  to　all　species　of　plant　or　to　a　single　species。　So　in　these
  universal　and　commensurate　connexions　the　'middle'　and　its　effect　must
  reciprocate；　i。e。　be　convertible。　Supposing；　for　example；　that　the
  reason　why　trees　are　deciduous　is　the　coagulation　of　sap；　then　if　a
  tree　is　deciduous；　coagulation　must　be　present；　and　if　coagulation
  is　present…not　in　any　subject　but　in　a　tree…then　that　tree　must　be
  deciduous。
  17
  Can　the　cause　of　an　identical　effect　be　not　identical　in　every
  instance　of　the　effect　but　different？　Or　is　that　impossible？　Perhaps
  it　is　impossible　if　the　effect　is　demonstrated　as　essential　and　not　as
  inhering　in　virtue　of　a　symptom　or　an　accident…because　the　middle　is
  then　the　definition　of　the　major　term…though　possible　if　the
  demonstration　is　not　essential。　Now　it　is　possible　to　consider　the
  effect　and　its　subject　as　an　accidental　conjunction；　though　such
  conjunctions　would　not　be　regarded　as　connexions　demanding
  scientific　proof。　But　if　they　are　accepted　as　such；　the　middle　will
  correspond　to　the　extremes；　and　be　equivocal　if　they　are　equivocal；
  generically　one　if　they　are　generically　one。　Take　the　question　why
  proportionals　alternate。　The　cause　when　they　are　lines；　and　when
  they　are　numbers；　is　both　different　and　identical；　different　in　so　far
  as　lines　are　lines　and　not　numbers；　identical　as　involving　a　given
  determinate　increment。　In　all　proportionals　this　is　so。　Again；　the
  cause　of　likeness　between　colour　and　colour　is　other　than　that　between
  figure　and　figure；　for　likeness　here　is　equivocal；　meaning　perhaps
  in　the　latter　case　equality　of　the　ratios　of　the　sides　and　equality　of
  the　angles；　in　the　case　of　colours　identity　of　the　act　of　perceiving
  them；　or　something　else　of　the　sort。　Again；　connexions　requiring　proof
  which　are　identical　by　analogy　middles　also　analogous。
  The　truth　is　that　cause；　effect；　and　subject　are　reciprocally
  predicable　in　the　following　way。　If　the　species　are　taken　severally；
  the　effect　is　wider　than　the　subject　（e。g。　the　possession　of
  external　angles　equal　to　four　right　angles　is　an　attribute　wider
  than　triangle　or　are）；　but　it　is　coextensive　with　the　species　taken
  collectively　（in　this　instance　with　all　figures　whose　external
  angles　are　equal　to　four　right　angles）。　And　the　middle　likewise
  reciprocates；　for　the　middle　is　a　definition　of　the　major；　which　is
  incidentally　the　reason　why　all　the　sciences　are　built　up　through
  definition。
  We　may　illustrate　as　follows。　Deciduous　is　a　universal　attribute
  of　vine；　and　is　at　the　same　time　of　wider　extent　than　vine；　and　of
  fig；　and　is　of　wider　extent　than　fig：　but　it　is　not　wider　than　but
  coextensive　with　the　totality　of　the　species。　Then　if　you　take　the
  middle　which　is　proximate；　it　is　a　definition　of　deciduous。　I　say
  that；　because　you　will　first　reach　a　middle　next　the　subject；　and　a
  premiss　asserting　it　of　the　whole　subject；　and　after　that　a　middle…the
  coagulation　of　sap　or　something　of　the　sort…proving　the　connexion　of
  the　first　middle　with　the　major：　but　it　is　the　coagulation　of　sap　at
  the　junction　of　leaf…stalk　and　stem　which　defines　deciduous。
  If　an　explanation　in　formal　terms　of　the　inter…relation　of　cause　and
  effect　is　demanded；　we　shall　offer　the　following。　Let　A　be　an
  attribute　of　all　B；　and　B　of　every　species　of　D；　but　so　that　both　A
  and　B　are　wider　than　their　respective　subjects。　Then　B　will　be　a
  universal　attribute　of　each　species　of　D　（since　I　call　such　an
  attribute　universal　even　if　it　is　not　commensurate；　and　I　call　an
  attribute　primary　universal　if　it　is　commensurate；　not　with　each
  species　severally　but　with　their　totality）；　and　it　extends　beyond　each
  of　them　taken　separately。
  Thus；　B　is　the　cause　of　A's　inherence　in　the　species　of　D：
  consequently　A　must　be　of　wider　extent　than　B；　otherwise　why　should
  B　be　the　cause　of　A's　inherence　in　D　any　more　than　A　the　cause　of
  B's　inherence　in　D？　Now　if　A　is　an　attribute　of　all　the　species　of
  E；　all　the　species　of　E　will　be　united　by　possessing　some　common　cause
  other　than　B：　otherwise　how　shall　we　be　able　to　say　that　A　is
  predicable　of　all　of　which　E　is　predicable；　while　E　is　not
  predicable　of　all　of　which　A　can　be　predicated？　I　mean　how　can　there
  fail　to　be　some　special　cause　of　A's　inherence　in　E；　as　there　was　of
  A's　inherence　in　all　the　species　of　D？　Then　are　the　species　of　E；　too；
  united　by　possessing　some　common　cause？　This　cause　we　must　look　for。
  Let　us　call　it　C。
  We　conclude；　then；　that　the　same　effect　may　have　more　than　one
  cause；　but　not　in　subjects　specifically　identical。　For　instance；　the
  cause　of　longevity　in　quadrupeds　is　lack　of　bile；　in　birds　a　dry
  constitution…or　certainly　something　different。
  18
  If　immediate　premisses　are　not　reached　at　once；　and　there　is　not
  merely　one　middle　but　several　middles；　i。e。　several　causes；　is　the
  cause　of　the　property's　inherence　in　the　several　species　the　middle
  which　is　proximate　to　the　primary　universal；　or　the　middle　which　is
  proximate　to　the　species？　Clearly　the　cause　is　that　nearest　to　each
  species　severally　in　which　it　is　manifested；　for　that　is　the　cause
  of　the　subject's　falling　under　the　universal。　To　illustrate
  formally：　C　is　the　cause　of　B's　inherence　in　D；　hence　C　is　the　cause
  of　A's　inherence　in　D；　B　of　A's　inherence　in　C；　while　the　cause　of　A's
  inherence　in　B　is　B　itself。
  19
  As　regards　syllogism　and　demonstration；　the　definition　of；　and　the
  conditions　required　to　produce　each　of　them；　are　now　clear；　and　with
  that　also　the　definition　of；　and　the　conditions　required　to　produce；
  demonstrative　knowledge；　since　it　is　the　same　as　demonstration。　As
  to　the　basic　premisses；　how　they　become　known　and　what　is　the
  developed　state　of　knowledge　of　them　is　made　clear　by　raising　some
  preliminary　problems。
  We　have　already　said　that　scientific　knowledge　through　demonstration
  is　impossible　unless　a　man　knows　the　primary　immediate　premisses。
  But　there　are　questions　which　might　be　raised　in　respect　of　the
  apprehension　of　these　immediate　premisses：　one　might　not　only　ask
  whether　it　is　of　the　same　kind　as　the　apprehension　of　the　conclusions；
  but　also　whether　there　is　or　is　not　scientific　knowledge　of　both；　or
  scientific　knowledge　of　the　latter；　and　of　the　former　a　different　kind
  of　knowledge；　and；　further；　whether　the　developed　states　of
  knowledge　are　not　innate　but　come　to　be　in　us；　or　are　inna