POSTERIOR　ANALYTICS
  by　Aristotle
  translated　by　G。　R。　G。　Mure
  Book　I
  1
  ALL　instruction　given　or　received　by　way　of　argument　proceeds　from
  pre…existent　knowledge。　This　becomes　evident　upon　a　survey　of　all
  the　species　of　such　instruction。　The　mathematical　sciences　and　all
  other　speculative　disciplines　are　acquired　in　this　way；　and　so　are　the
  two　forms　of　dialectical　reasoning；　syllogistic　and　inductive；　for
  each　of　these　latter　make　use　of　old　knowledge　to　impart　new；　the
  syllogism　assuming　an　audience　that　accepts　its　premisses；　induction
  exhibiting　the　universal　as　implicit　in　the　clearly　known
  particular。　Again；　the　persuasion　exerted　by　rhetorical　arguments　is
  in　principle　the　same；　since　they　use　either　example；　a　kind　of
  induction；　or　enthymeme；　a　form　of　syllogism。
  The　pre…existent　knowledge　required　is　of　two　kinds。　In　some　cases
  admission　of　the　fact　must　be　assumed；　in　others　comprehension　of
  the　meaning　of　the　term　used；　and　sometimes　both　assumptions　are
  essential。　Thus；　we　assume　that　every　predicate　can　be　either　truly
  affirmed　or　truly　denied　of　any　subject；　and　that　'triangle'　means
  so　and　so；　as　regards　'unit'　we　have　to　make　the　double　assumption
  of　the　meaning　of　the　word　and　the　existence　of　the　thing。　The
  reason　is　that　these　several　objects　are　not　equally　obvious　to　us。
  Recognition　of　a　truth　may　in　some　cases　contain　as　factors　both
  previous　knowledge　and　also　knowledge　acquired　simultaneously　with
  that　recognition…knowledge；　this　latter；　of　the　particulars　actually
  falling　under　the　universal　and　therein　already　virtually　known。　For
  example；　the　student　knew　beforehand　that　the　angles　of　every　triangle
  are　equal　to　two　right　angles；　but　it　was　only　at　the　actual　moment　at
  which　he　was　being　led　on　to　recognize　this　as　true　in　the　instance
  before　him　that　he　came　to　know　'this　figure　inscribed　in　the
  semicircle'　to　be　a　triangle。　For　some　things　（viz。　the　singulars
  finally　reached　which　are　not　predicable　of　anything　else　as
  subject）　are　only　learnt　in　this　way；　i。e。　there　is　here　no
  recognition　through　a　middle　of　a　minor　term　as　subject　to　a　major。
  Before　he　was　led　on　to　recognition　or　before　he　actually　drew　a
  conclusion；　we　should　perhaps　say　that　in　a　manner　he　knew；　in　a
  manner　not。
  If　he　did　not　in　an　unqualified　sense　of　the　term　know　the　existence
  of　this　triangle；　how　could　he　know　without　qualification　that　its
  angles　were　equal　to　two　right　angles？　No：　clearly　he　knows　not
  without　qualification　but　only　in　the　sense　that　he　knows　universally。
  If　this　distinction　is　not　drawn；　we　are　faced　with　the　dilemma　in　the
  Meno：　either　a　man　will　learn　nothing　or　what　he　already　knows；　for　we
  cannot　accept　the　solution　which　some　people　offer。　A　man　is　asked；
  'Do　you；　or　do　you　not；　know　that　every　pair　is　even？'　He　says　he　does
  know　it。　The　questioner　then　produces　a　particular　pair；　of　the
  existence；　and　so　a　fortiori　of　the　evenness；　of　which　he　was　unaware。
  The　solution　which　some　people　offer　is　to　assert　that　they　do　not
  know　that　every　pair　is　even；　but　only　that　everything　which　they　know
  to　be　a　pair　is　even：　yet　what　they　know　to　be　even　is　that　of　which
  they　have　demonstrated　evenness；　i。e。　what　they　made　the　subject　of
  their　premiss；　viz。　not　merely　every　triangle　or　number　which　they
  know　to　be　such；　but　any　and　every　number　or　triangle　without
  reservation。　For　no　premiss　is　ever　couched　in　the　form　'every
  number　which　you　know　to　be　such'；　or　'every　rectilinear　figure
  which　you　know　to　be　such'：　the　predicate　is　always　construed　as
  applicable　to　any　and　every　instance　of　the　thing。　On　the　other
  hand；　I　imagine　there　is　nothing　to　prevent　a　man　in　one　sense　knowing
  what　he　is　learning；　in　another　not　knowing　it。　The　strange　thing
  would　be；　not　if　in　some　sense　he　knew　what　he　was　learning；　but　if　he
  were　to　know　it　in　that　precise　sense　and　manner　in　which　he　was
  learning　it。
  2
  We　suppose　ourselves　to　possess　unqualified　scientific　knowledge
  of　a　thing；　as　opposed　to　knowing　it　in　the　accidental　way　in　which
  the　sophist　knows；　when　we　think　that　we　know　the　cause　on　which　the
  fact　depends；　as　the　cause　of　that　fact　and　of　no　other；　and；　further；
  that　the　fact　could　not　be　other　than　it　is。　Now　that　scientific
  knowing　is　something　of　this　sort　is　evident…witness　both　those　who
  falsely　claim　it　and　those　who　actually　possess　it；　since　the　former
  merely　imagine　themselves　to　be；　while　the　latter　are　also　actually；
  in　the　condition　described。　Consequently　the　proper　object　of
  unqualified　scientific　knowledge　is　something　which　cannot　be　other
  than　it　is。
  There　may　be　another　manner　of　knowing　as　well…that　will　be
  discussed　later。　What　I　now　assert　is　that　at　all　events　we　do　know　by
  demonstration。　By　demonstration　I　mean　a　syllogism　productive　of
  scientific　knowledge；　a　syllogism；　that　is；　the　grasp　of　which　is　eo
  ipso　such　knowledge。　Assuming　then　that　my　thesis　as　to　the　nature
  of　scientific　knowing　is　correct；　the　premisses　of　demonstrated
  knowledge　must　be　true；　primary；　immediate；　better　known　than　and
  prior　to　the　conclusion；　which　is　further　related　to　them　as　effect　to
  cause。　Unless　these　conditions　are　satisfied；　the　basic　truths　will
  not　be　'appropriate'　to　the　conclusion。　Syllogism　there　may　indeed
  be　without　these　conditions；　but　such　syllogism；　not　being
  productive　of　scientific　knowledge；　will　not　be　demonstration。　The
  premisses　must　be　true：　for　that　which　is　non…existent　cannot　be
  known…we　cannot　know；　e。g。　that　the　diagonal　of　a　square　is
  commensurate　with　its　side。　The　premisses　must　be　primary　and
  indemonstrable；　otherwise　they　will　require　demonstration　in　order
  to　be　known；　since　to　have　knowledge；　if　it　be　not　accidental
  knowledge；　of　things　which　are　demonstrable；　means　precisely　to　have　a
  demonstration　of　them。　The　premisses　must　be　the　causes　of　the
  conclusion；　better　known　than　it；　and　prior　to　it；　its　causes；　since
  we　possess　scientific　knowledge　of　a　thing　only　when　we　know　its
  cause；　prior；　in　order　to　be　causes；　antecedently　known；　this
  antecedent　knowledge　being　not　our　mere　understanding　of　the
  meaning；　but　knowledge　of　the　fact　as　well。　Now　'prior'　and　'better
  known'　are　ambiguous　terms；　for　there　is　a　difference　between　what
  is　prior　and　better　known　in　the　order　of　being　and　what　is　prior
  and　better　known　to　man。　I　mean　that　objects　nearer　to　sense　are　prior
  and　better　known　to　man；　objects　without　qualification　prior　and
  better　known　are　those　further　from　sense。　Now　the　most　universal
  causes　are　furthest　from　sense　and　particular　causes　are　nearest　to
  sense；　and　they　are　thus　exactly　opposed　to　one　another。　In　saying
  that　the　premisses　of　demonstrated　knowledge　must　be　primary；　I　mean
  that　they　must　be　the　'appropriate'　basic　truths；　for　I　identify
  primary　premiss　and　basic　truth。　A　'basic　truth'　in　a　demonstration　is
  an　immediate　proposition。　An　immediate　proposition　is　one　which　has　no
  other　proposition　prior　to　it。　A　proposition　is　either　part　of　an
  enunciation；　i。e。　it　predicates　a　single　attribute　of　a　single
  subject。　If　a　proposition　is　dialectical；　it　assumes　either　part
  indifferently；　if　it　is　demonstrative；　it　lays　down　one　part　to　the
  definite　exclusion　of　the　other　because　that　part　is　true。　The　term
  'enunciation'　denotes　either　part　of　a　contradiction　indifferently。
  A　contradiction　is　an　opposition　which　of　its　own　nature　excludes　a
  middle。　The　part　of　a　contradiction　which　conjoins　a　predicate　with
  a　subject　is　an　affirmation；　the　part　disjoining　them　is　a　negation。　I
  call　an　immediate　basic　truth　of　syllogism　a　'thesis'　when；　though
  it　is　not　susceptible　of　proof　by　the　teacher；　yet　ignorance　of　it
  does　not　constitute　a　total　bar　to　progress　on　the　part　of　the
  pupil：　one　which　the　pupil　must　know　if　he　is　to　learn　anything
  whatever　is　an　axiom。　I　call　it　an　axiom　because　there　are　such　truths
  and　we　give　them　the　name　of　axioms　par　excellence。　If　a　thesis
  assumes　one　part　or　the　other　of　an　enunciation；　i。e。　asserts　either
  the　existence　or　the　non…existence　of　a　subject；　it　is　a　hypothesis；
  if　it　does　not　so　assert；　it　is　a　definition。　Definition　is　a　'thesis'
  or　a　'laying　something　down'；　since　the　arithmetician　lays　it　down
  that　to　be　a　unit