ON　SLEEP　AND　SLEEPLESSNESS
  by　Aristotle
  translated　by　J。　I。　Beare
  1
  WITH　regard　to　sleep　and　waking；　we　must　consider　what　they　are：
  whether　they　are　peculiar　to　soul　or　to　body；　or　common　to　both；　and
  if　common；　to　what　part　of　soul　or　body　they　appertain：　further；
  from　what　cause　it　arises　that　they　are　attributes　of　animals；　and
  whether　all　animals　share　in　them　both；　or　some　partake　of　the　one
  only；　others　of　the　other　only；　or　some　partake　of　neither　and　some　of
  both。
  Further；　in　addition　to　these　questions；　we　must　also　inquire　what
  the　dream　is；　and　from　what　cause　sleepers　sometimes　dream；　and
  sometimes　do　not；　or　whether　the　truth　is　that　sleepers　always　dream
  but　do　not　always　remember　（their　dream）；　and　if　this　occurs；　what　its
  explanation　is。
  Again；　＇we　must　inquire＇　whether　it　is　possible　or　not　to　foresee
  the　future　（in　dreams）；　and　if　it　be　possible；　in　what　manner；
  further；　whether；　supposing　it　possible；　it　extends　only　to　things
  to　be　accomplished　by　the　agency　of　Man；　or　to　those　also　of　which　the
  cause　lies　in　supra…human　agency；　and　which　result　from　the　workings
  of　Nature；　or　of　Spontaneity。
  First；　then；　this　much　is　clear；　that　waking　and　sleep　appertain
  to　the　same　part　of　an　animal；　inasmuch　as　they　are　opposites；　and
  sleep　is　evidently　a　privation　of　waking。　For　contraries；　in　natural
  as　well　as　in　all　other　matters；　are　seen　always　to　present　themselves
  in　the　same　subject；　and　to　be　affections　of　the　same：　examples
  are…health　and　sickness；　beauty　and　ugliness；　strength　and　weakness；
  sight　and　blindness；　hearing　and　deafness。　This　is　also　clear　from　the
  following　considerations。　The　criterion　by　which　we　know　the　waking
  person　to　be　awake　is　identical　with　that　by　which　we　know　the　sleeper
  to　be　asleep；　for　we　assume　that　one　who　is　exercising
  sense…perception　is　awake；　and　that　every　one　who　is　awake　perceives
  either　some　external　movement　or　else　some　movement　in　his　own
  consciousness。　If　waking；　then；　consists　in　nothing　else　than　the
  exercise　of　sense…perception；　the　inference　is　clear；　that　the
  organ；　in　virtue　of　which　animals　perceive；　is　that　by　which　they
  wake；　when　they　are　awake；　or　sleep；　when　they　are　awake；　or　sleep；
  when　they　are　asleep。
  But　since　the　exercise　of　sense…perception　does　not　belong　to　soul
  or　body　exclusively；　then　（since　the　subject　of　actuality　is　in
  every　case　identical　with　that　of　potentiality；　and　what　is　called
  sense…perception；　as　actuality；　is　a　movement　of　the　soul　through
  the　body）　it　is　clear　that　its　affection　is　not　an　affection　of　soul
  exclusively；　and　that　a　soulless　body　has　not　the　potentiality　of
  perception。　＇Thus　sleep　and　waking　are　not　attributes　of　pure
  intelligence；　on　the　one　hand；　or　of　inanimate　bodies；　on　the　other。＇
  Now；　whereas　we　have　already　elsewhere　distinguished　what　are　called
  the　parts　of　the　soul；　and　whereas　the　nutrient　is；　in　all　living
  bodies；　capable　of　existing　without　the　other　parts；　while　none　of　the
  others　can　exist　without　the　nutrient；　it　is　clear　that　sleep　and
  waking　are　not　affections　of　such　living　things　as　partake　only　of
  growth　and　decay；　e。g。　not　of　plants；　because　these　have　not　the
  faculty　of　sense…perception；　whether　or　not　this　be　capable　of
  separate　existence；　in　its　potentiality；　indeed；　and　in　its
  relationships；　it　is　separable。
  Likewise　it　is　clear　that　＇of　those　which　either　sleep　or　wake＇
  there　is　no　animal　which　is　always　awake　or　always　asleep；　but　that
  both　these　affections　belong　＇alternately＇　to　the　same　animals。　For　if
  there　be　an　animal　not　endued　with　sense…perception；　it　is
  impossible　that　this　should　either　sleep　or　wake；　since　both　these　are
  affections　of　the　activity　of　the　primary　faculty　of　sense…perception。
  But　it　is　equally　impossible　also　that　either　of　these　two
  affections　should　perpetually　attach　itself　to　the　same　animal；　e。g。
  that　some　species　of　animal　should　be　always　asleep　or　always　awake；
  without　intermission；　for　all　organs　which　have　a　natural　function
  must　lose　power　when　they　work　beyond　the　natural　time…limit　of
  their　working　period；　for　instance；　the　eyes　＇must　lose　power＇　from
  ＇too　long　continued＇　seeing；　and　must　give　it　up；　and　so　it　is　with
  the　hand　and　every　other　member　which　has　a　function。　Now；　if
  sense…perception　is　the　function　of　a　special　organ；　this　also；　if
  it　continues　perceiving　beyond　the　appointed　time…limit　of　its
  continuous　working　period；　will　lose　its　power；　and　will　do　its　work
  no　longer。　Accordingly；　if　the　waking　period　is　determined　by　this
  fact；　that　in　it　sense…perception　is　free；　if　in　the　case　of　some
  contraries　one　of　the　two　must　be　present；　while　in　the　case　of　others
  this　is　not　necessary；　if　waking　is　the　contrary　of　sleeping；　and
  one　of　these　two　must　be　present　to　every　animal：　it　must　follow
  that　the　state　of　sleeping　is　necessary。　Finally；　if　such　affection　is
  Sleep；　and　this　is　a　state　of　powerlessness　arising　from　excess　of
  waking；　and　excess　of　waking　is　in　its　origin　sometimes　morbid；
  sometimes　not；　so　that　the　powerlessness　or　dissolution　of　activity
  will　be　so　or　not；　it　is　inevitable　that　every　creature　which　wakes
  must　also　be　capable　of　sleeping；　since　it　is　impossible　that　it
  should　continue　actualizing　its　powers　perpetually。
  So；　also；　it　is　impossible　for　any　animal　to　continue　always
  sleeping。　For　sleep　is　an　affection　of　the　organ　of
  sense…perceptiona　sort　of　tie　or　inhibition　of　function　imposed　on
  it；　so　that　every　creature　that　sleeps　must　needs　have　the　organ　of
  sense…perception。　Now；　that　alone　which　is　capable　of　sense…perception
  in　actuality　has　the　faculty　of　sense…perception；　but　to　realize
  this　faculty；　in　the　proper　and　unqualified　sense；　is　impossible　while
  one　is　asleep。　All　sleep；　therefore；　must　be　susceptible　of　awakening。
  Accordingly；　almost　all　other　animals　are　clearly　observed　to
  partake　in　sleep；　whether　they　are　aquatic；　aerial；　or　terrestrial；
  since　fishes　of　all　kinds；　and　molluscs；　as　well　as　all　others　which
  have　eyes；　have　been　seen　sleeping。　'Hard…eyed'　creatures　and
  insects　manifestly　assume　the　posture　of　sleep；　but　the　sleep　of　all
  such　creatures　is　of　brief　duration；　so　that　often　it　might　well
  baffle　one's　observation　to　decide　whether　they　sleep　or　not。　Of
  testaceous　animals；　on　the　contrary；　no　direct　sensible　evidence　is　as
  yet　forthcoming　to　determine　whether　they　sleep；　but　if　the　above
  reasoning　be　convincing　to　any　one；　he　who　follows　it　will　admit
  this　＇viz。　that　they　do　so。＇
  That；　therefore；　all　animals　sleep　may　be　gathered　from　these
  considerations。　For　an　animal　is　defined　as　such　by　its　possessing
  sense…perception；　and　we　assert　that　sleep　is；　in　a　certain　way；　an
  inhibition　of　function；　or；　as　it　were；　a　tie；　imposed　on
  sense…perception；　while　its　loosening　or　remission　constitutes　the
  being　awake。　But　no　plant　can　partake　in　either　of　these　affections；
  for　without　sense…perception　there　is　neither　sleeping　nor　waking。　But
  creatures　which　have　sense…perception　have　likewise　the　feeling　of
  pain　and　pleasure；　while　those　which　have　these　have　appetite　as　well；
  but　plants　have　none　of　these　affections。　A　mark　of　this　is　that　the
  nutrient　part　does　its　own　work　better　when　（the　animal）　is　asleep
  than　when　it　is　awake。　Nutrition　and　growth　are　then　especially
  promoted；　a　fact　which　implies　that　creatures　do　not　need
  sense…perception　to　assist　these　processes。
  2
  We　must　now　proceed　to　inquire　into　the　cause　why　one　sleeps　and
  wakes；　and　into　the　particular　nature　of　the　sense…perception；　or
  sense…perceptions；　if　there　be　several；　on　which　these　affections
  depend。　Since；　then；　some　animals　possess　all　the　modes　of
  sense…perception；　and　some　not　all；　not；　for　example；　sight；　while　all
  possess　touch　and　taste；　except　such　animals　as　are　imperfectly
  developed；　a　class　of　which　we　have　already　treated　in　our　work　on　the
  soul；　and　since　an　animal　when　asleep　is　unable　to　exercise；　in　the
  simple　sense　any　particular　sensory　faculty　whatever；　it　follows
  that　in　the　state　called　sleep　the　same　affection　must　extend　to　all
  the　special　senses；　because；　if　it　attaches　itself　to　one　of　them
  but　not　to　another；　then　an　animal　while　asleep　may　perceive　with
  the　latter；　but　this　is　impossible。
  Now；　s