ON　DREAMS
  by　Aristotle
  translated　by　J。　I。　Beare
  1
  WE　must；　in　the　next　place；　investigate　the　subject　of　the　dream；
  and　first　inquire　to　which　of　the　faculties　of　the　soul　it　presents
  itself；　i。e。　whether　the　affection　is　one　which　pertains　to　the
  faculty　of　intelligence　or　to　that　of　sense…perception；　for　these
  are　the　only　faculties　within　us　by　which　we　acquire　knowledge。
  If；　then；　the　exercise　of　the　faculty　of　sight　is　actual　seeing；
  that　of　the　auditory　faculty；　hearing；　and；　in　general　that　of　the
  faculty　of　sense…perception；　perceiving；　and　if　there　are　some
  perceptions　common　to　the　senses；　such　as　figure；　magnitude；　motion；
  &c。；　while　there　are　others；　as　colour；　sound；　taste；　peculiar　＇each
  to　its　own　sense＇；　and　further；　if　all　creatures；　when　the　eyes　are
  closed　in　sleep；　are　unable　to　see；　and　the　analogous　statement　is
  true　of　the　other　senses；　so　that　manifestly　we　perceive　nothing
  when　asleep；　we　may　conclude　that　it　is　not　by　sense…perception　we
  perceive　a　dream。
  But　neither　is　it　by　opinion　that　we　do　so。　For　＇in　dreams＇　we　not
  only　assert；　e。g。　that　some　object　approaching　is　a　man　or　a　horse
  ＇which　would　be　an　exercise　of　opinion＇；　but　that　the　object　is
  white　or　beautiful；　points　on　which　opinion　without　sense…perception
  asserts　nothing　either　truly　or　falsely。　It　is；　however；　a　fact　that
  the　soul　makes　such　assertions　in　sleep。　We　seem　to　see　equally　well
  that　the　approaching　figure　is　a　man；　and　that　it　is　white。　＇In
  dreams＇；　too；　we　think　something　else；　over　and　above　the　dream
  presentation；　just　as　we　do　in　waking　moments　when　we　perceive
  something；　for　we　often　also　reason　about　that　which　we　perceive。
  So；　too；　in　sleep　we　sometimes　have　thoughts　other　than　the　mere
  phantasms　immediately　before　our　minds。　This　would　be　manifest　to
  any　one　who　should　attend　and　try；　immediately　on　arising　from
  sleep；　to　remember　＇his　dreaming　experience＇。　There　are　cases　of
  persons　who　have　seen　such　dreams；　those；　for　example；　who　believe
  themselves　to　be　mentally　arranging　a　given　list　of　subjects　according
  to　the　mnemonic　rule。　They　frequently　find　themselves　engaged　in
  something　else　besides　the　dream；　viz。　in　setting　a　phantasm　which
  they　envisage　into　its　mnemonic　position。　Hence　it　is　plain　that　not
  every　'phantasm'　in　sleep　is　a　mere　dream…image；　and　that　the
  further　thinking　which　we　perform　then　is　due　to　an　exercise　of　the
  faculty　of　opinion。
  So　much　at　least　is　plain　on　all　these　points；　viz。　that　the　faculty
  by　which；　in　waking　hours；　we　are　subject　to　illusion　when　affected　by
  disease；　is　identical　with　that　which　produces　illusory　effects　in
  sleep。　So；　even　when　persons　are　in　excellent　health；　and　know　the
  facts　of　the　case　perfectly　well；　the　sun；　nevertheless；　appears　to
  them　to　be　only　a　foot　wide。　Now；　whether　the　presentative　faculty
  of　the　soul　be　identical　with；　or　different　from；　the　faculty　of
  sense…perception；　in　either　case　the　illusion　does　not　occur　without
  our　actually　seeing　or　＇otherwise＇　perceiving　something。　Even　to　see
  wrongly　or　to　hear　wrongly　can　happen　only　to　one　who　sees　or　hears
  something　real；　though　not　exactly　what　he　supposes。　But　we　have
  assumed　that　in　sleep　one　neither　sees；　nor　hears；　nor　exercises　any
  sense　whatever。　Perhaps　we　may　regard　it　as　true　that　the　dreamer　sees
  nothing；　yet　as　false　that　his　faculty　of　sense…perception　is
  unaffected；　the　fact　being　that　the　sense　of　seeing　and　the　other
  senses　may　possibly　be　then　in　a　certain　way　affected；　while　each　of
  these　affections；　as　duly　as　when　he　is　awake；　gives　its　impulse　in
  a　certain　manner　to　his　＇primary＇　faculty　of　sense；　though　not　in
  precisely　the　same　manner　as　when　he　is　awake。　Sometimes；　too；　opinion
  says　＇to　dreamers＇　just　as　to　those　who　are　awake；　that　the　object
  seen　is　an　illusion；　at　other　times　it　is　inhibited；　and　becomes　a
  mere　follower　of　the　phantasm。
  It　is　plain　therefore　that　this　affection；　which　we　name　'dreaming'；
  is　no　mere　exercise　of　opinion　or　intelligence；　but　yet　is　not　an
  affection　of　the　faculty　of　perception　in　the　simple　sense。　If　it　were
  the　latter　it　would　be　possible　＇when　asleep＇　to　hear　and　see　in　the
  simple　sense。
  How　then；　and　in　what　manner；　it　takes　place；　is　what　we　have　to
  examine。　Let　us　assume；　what　is　indeed　clear　enough；　that　the
  affection　＇of　dreaming＇　pertains　to　sense…perception　as　surely　as
  sleep　itself　does。　For　sleep　does　not　pertain　to　one　organ　in
  animals　and　dreaming　to　another；　both　pertain　to　the　same　organ。
  But　since　we　have；　in　our　work　On　the　Soul；　treated　of　presentation；
  and　the　faculty　of　presentation　is　identical　with　that　of
  sense…perception；　though　the　essential　notion　of　a　faculty　of
  presentation　is　different　from　that　of　a　faculty　of
  sense…perception；　and　since　presentation　is　the　movement　set　up　by　a
  sensory　faculty　when　actually　discharging　its　function；　while　a
  dream　appears　to　be　a　presentation　（for　a　presentation　which　occurs　in
  sleep…whether　simply　or　in　some　particular　way…is　what　we　call　a
  dream）：　it　manifestly　follows　that　dreaming　is　an　activity　of　the
  faculty　of　sense…perception；　but　belongs　to　this　faculty　qua
  presentative。
  2
  We　can　best　obtain　a　scientific　view　of　the　nature　of　the　dream
  and　the　manner　in　which　it　originates　by　regarding　it　in　the　light
  of　the　circumstances　attending　sleep。　The　objects　of
  sense…perception　corresponding　to　each　sensory　organ　produce
  sense…perception　in　us；　and　the　affection　due　to　their　operation　is
  present　in　the　organs　of　sense　not　only　when　the　perceptions　are
  actualized；　but　even　when　they　have　departed。
  What　happens　in　these　cases　may　be　compared　with　what　happens　in　the
  case　of　projectiles　moving　in　space。　For　in　the　case　of　these　the
  movement　continues　even　when　that　which　set　up　the　movement　is　no
  longer　in　contact　＇with　the　things　that　are　moved＇。　For　that　which　set
  them　in　motion　moves　a　certain　portion　of　air；　and　this；　in　turn；
  being　moved　excites　motion　in　another　portion；　and　so；　accordingly；　it
  is　in　this　way　that　＇the　bodies＇；　whether　in　air　or　in　liquids；
  continue　moving；　until　they　come　to　a　standstill。
  This　we　must　likewise　assume　to　happen　in　the　case　of　qualitative
  change；　for　that　part　which　＇for　example＇　has　been　heated　by　something
  hot；　heats　＇in　turn＇　the　part　next　to　it；　and　this　propagates　the
  affection　continuously　onwards　until　the　process　has　come　round　to　its
  oint　of　origination。　This　must　also　happen　in　the　organ　wherein　the
  exercise　of　sense…perception　takes　place；　since　sense…perception；　as
  realized　in　actual　perceiving；　is　a　mode　of　qualitative　change。　This
  explains　why　the　affection　continues　in　the　sensory　organs；　both　in
  their　deeper　and　in　their　more　superficial　parts；　not　merely　while
  they　are　actually　engaged　in　perceiving；　but　even　after　they　have
  ceased　to　do　so。　That　they　do　this；　indeed；　is　obvious　in　cases
  where　we　continue　for　some　time　engaged　in　a　particular　form　of
  perception；　for　then；　when　we　shift　the　scene　of　our　perceptive
  activity；　the　previous　affection　remains；　for　instance；　when　we　have
  turned　our　gaze　from　sunlight　into　darkness。　For　the　result　of　this　is
  that　one　sees　nothing；　owing　to　the　excited　by　the　light　still
  subsisting　in　our　eyes。　Also；　when　we　have　looked　steadily　for　a
  long　while　at　one　colour；　e。g。　at　white　or　green；　that　to　which　we
  next　transfer　our　gaze　appears　to　be　of　the　same　colour。　Again　if；
  after　having　looked　at　the　sun　or　some　other　brilliant　object；　we
  close　the　eyes；　then；　if　we　watch　carefully；　it　appears　in　a　right
  line　with　the　direction　of　vision　（whatever　this　may　be）；　at　first
  in　its　own　colour；　then　it　changes　to　crimson；　next　to　purple；　until
  it　becomes　black　and　disappears。　And　also　when　persons　turn　away
  from　looking　at　objects　in　motion；　e。g。　rivers；　and　especially　those
  which　flow　very　rapidly；　they　find　that　the　visual　stimulations
  still　present　themselves；　for　the　things　really　at　rest　are　then
  seen　moving：　persons　become　very　deaf　after　hearing　loud　noises；　and
  after　smelling　very　strong　odours　their　power　of　smelling　is　impaired；
  and　similarly　in　other　cases。　These　phenomena　manifestly　take　place　in
  the　way　above　described。
  That　the　sensory　organs　are　acutely　sensitive　to　even　a　slight
  qualitative　difference　＇in　their　objects＇　is　shown　by　what　happens
  in　the　case　of　mirrors；　a　subject　to　which；　even　taking　it
  independently；　one　might　devote　close　consideration　and　inquiry。　At
  the　same　time　it　becomes　plain　from　them　that　as　the　eye　＇in　seeing＇