inciples。　That　is　why　（with　one　exception）　all　those　who　define　the　soul　by　its　power　of　knowing　make　it　either　an　element　or　constructed　out　of　the　elements。　The　language　they　all　use　is　similar；　like；　they　say；　is　known　by　like；　as　the　soul　knows　everything；　they　construct　it　out　of　all　the　principles。　Hence　all　those　who　admit　but　one　cause　or　element；　make　the　soul　also　one　（e。g。　fire　or　air）；　while　those　who　admit　a　multiplicity　of　principles　make　the　soul　also　multiple。　The　exception　is　Anaxagoras；　he　alone　says　that　mind　is　impassible　and　has　nothing　in　common　with　anything　else。　But；　if　this　is　so；　how　or　in　virtue　of　what　cause　can　it　know？　That　Anaxagoras　has　not　explained；　nor　can　any　answer　be　inferred　from　his　words。　All　who　acknowledge　pairs　of　opposites　among　their　principles；　construct　the　soul　also　out　of　these　contraries；　while　those　who　admit　as　principles　only　one　contrary　of　each　pair；　e。g。　either　hot　or　cold；　likewise　make　the　soul　some　one　of　these。　That　is　why；　also；　they　allow　themselves　to　be　guided　by　the　names；　those　who　identify　soul　with　the　hot　argue　that　sen　（to　live）　is　derived　from　sein　（to　boil）；　while　those　who　identify　it　with　the　cold　say　that　soul　（psuche）　is　so　called　from　the　process　of　respiration　and　（katapsuxis）。　Such　are　the　traditional　opinions　concerning　soul；　together　with　the　grounds　on　which　they　are　maintained。
  3
  We　must　begin　our　examination　with　movement；　for　doubtless；　not　only　is　it　false　that　the　essence　of　soul　is　correctly　described　by　those　who　say　that　it　is　what　moves　（or　is　capable　of　moving）　itself；　but　it　is　an　impossibility　that　movement　should　be　even　an　attribute　of　it。　　　We　have　already　pointed　out　that　there　is　no　necessity　that　what　originates　movement　should　itself　be　moved。　There　are　two　senses　in　which　anything　may　be　moved…either　（a）　indirectly；　owing　to　something　other　than　itself；　or　（b）　directly；　owing　to　itself。　Things　are　'indirectly　moved'　which　are　moved　as　being　contained　in　something　which　is　moved；　e。g。　sailors　in　a　ship；　for　they　are　moved　in　a　different　sense　from　that　in　which　the　ship　is　moved；　the　ship　is　'directly　moved'；　they　are　'indirectly　moved'；　because　they　are　in　a　moving　vessel。　This　is　clear　if　we　consider　their　limbs；　the　movement　proper　to　the　legs　（and　so　to　man）　is　walking；　and　in　this　case　the　sailors　tare　not　walking。　Recognizing　the　double　sense　of　'being　moved'；　what　we　have　to　consider　now　is　whether　the　soul　is　'directly　moved'　and　participates　in　such　direct　movement。　　　There　are　four　species　of　movement…locomotion；　alteration；　diminution；　growth；　consequently　if　the　soul　is　moved；　it　must　be　moved　with　one　or　several　or　all　of　these　species　of　movement。　Now　if　its　movement　is　not　incidental；　there　must　be　a　movement　natural　to　it；　and；　if　so；　as　all　the　species　enumerated　involve　place；　place　must　be　natural　to　it。　But　if　the　essence　of　soul　be　to　move　itself；　its　being　moved　cannot　be　incidental　to…as　it　is　to　what　is　white　or　three　cubits　long；　they　too　can　be　moved；　but　only　incidentally…what　is　moved　is　that　of　which　'white'　and　'three　cubits　long'　are　the　attributes；　the　body　in　which　they　inhere；　hence　they　have　no　place：　but　if　the　soul　naturally　partakes　in　movement；　it　follows　that　it　must　have　a　place。　　　Further；　if　there　be　a　movement　natural　to　the　soul；　there　must　be　a　counter…movement　unnatural　to　it；　and　conversely。　The　same　applies　to　rest　as　well　as　to　movement；　for　the　terminus　ad　quem　of　a　thing's　natural　movement　is　the　place　of　its　natural　rest；　and　similarly　the　terminus　ad　quem　of　its　enforced　movement　is　the　place　of　its　enforced　rest。　But　what　meaning　can　be　attached　to　enforced　movements　or　rests　of　the　soul；　it　is　difficult　even　to　imagine。　　　Further；　if　the　natural　movement　of　the　soul　be　upward；　the　soul　must　be　fire；　if　downward；　it　must　be　earth；　for　upward　and　downward　movements　are　the　definitory　characteristics　of　these　bodies。　The　same　reasoning　applies　to　the　intermediate　movements；　termini；　and　bodies。　Further；　since　the　soul　is　observed　to　originate　movement　in　the　body；　it　is　reasonable　to　suppose　that　it　transmits　to　the　body　the　movements　by　which　it　itself　is　moved；　and　so；　reversing　the　order；　we　may　infer　from　the　movements　of　the　body　back　to　similar　movements　of　the　soul。　Now　the　body　is　moved　from　place　to　place　with　movements　of　locomotion。　Hence　it　would　follow　that　the　soul　too　must　in　accordance　with　the　body　change　either　its　place　as　a　whole　or　the　relative　places　of　its　parts。　This　carries　with　it　the　possibility　that　the　soul　might　even　quit　its　body　and　re…enter　it；　and　with　this　would　be　involved　the　possibility　of　a　resurrection　of　animals　from　the　dead。　But；　it　may　be　contended；　the　soul　can　be　moved　indirectly　by　something　else；　for　an　animal　can　be　pushed　out　of　its　course。　Yes；　but　that　to　whose　essence　belongs　the　power　of　being　moved　by　itself；　cannot　be　moved　by　something　else　except　incidentally；　just　as　what　is　good　by　or　in　itself　cannot　owe　its　goodness　to　something　external　to　it　or　to　some　end　to　which　it　is　a　means。　　　If　the　soul　is　moved；　the　most　probable　view　is　that　what　moves　it　is　sensible　things。　　　We　must　note　also　that；　if　the　soul　moves　itself；　it　must　be　the　mover　itself　that　is　moved；　so　that　it　follows　that　if　movement　is　in　every　case　a　displacement　of　that　which　is　in　movement；　in　that　respect　in　which　it　is　said　to　be　moved；　the　movement　of　the　soul　must　be　a　departure　from　its　essential　nature；　at　least　if　its　self…movement　is　essential　to　it；　not　incidental。　　　Some　go　so　far　as　to　hold　that　the　movements　which　the　soul　imparts　to　the　body　in　which　it　is　are　the　same　in　kind　as　those　with　which　it　itself　is　moved。　An　example　of　this　is　Democritus；　who　uses　language　like　that　of　the　comic　dramatist　Philippus；　who　accounts　for　the　movements　that　Daedalus　imparted　to　his　wooden　Aphrodite　by　saying　that　he　poured　quicksilver　into　it；　similarly　Democritus　says　that　the　spherical　atoms　which　according　to　him　constitute　soul；　owing　to　their　own　ceaseless　movements　draw　the　whole　body　after　them　and　so　produce　its　movements。　We　must　urge　the　question　whether　it　is　these　very　same　atoms　which　produce　rest　also…how　they　could　do　so；　it　is　difficult　and　even　impossible　to　say。　And；　in　general；　we　may　object　that　it　is　not　in　this　way　that　the　soul　appears　to　originate　movement　in　animals…it　is　through　intention　or　process　of　thinking。　　　It　is　in　the　same　fashion　that　the　Timaeus　also　tries　to　give　a　physical　account　of　how　the　soul　moves　its　body；　the　soul；　it　is　there　said；　is　in　movement；　and　so　owing　to　their　mutual　implication　moves　the　body　also。　After　compounding　the　soul…substance　out　of　the　elements　and　dividing　it　in　accordance　with　the　harmonic　numbers；　in　order　that　it　may　possess　a　connate　sensibility　for　'harmony'　and　that　the　whole　may　move　in　movements　well　attuned；　the　Demiurge　bent　the　straight　line　into　a　circle；　this　single　circle　he　divided　into　two　circles　united　at　two　common　points；　one　of　these　he　subdivided　into　seven　circles。　All　this　implies　that　the　movements　of　the　soul　are　identified　with　the　local　movements　of　the　heavens。　　　　　Now；　in　the　first　place；　it　is　a　mistake　to　say　that　the　soul　is　a　spatial　magnitude。　It　is　evident　that　Plato　means　the　soul　of　the　whole　to　be　like　the　sort　of　soul　which　is　called　mind　not　like　the　sensitive　or　the　desiderative　soul；　for　the　movements　of　neither　of　these　are　circular。　Now　mind　is　one　and　continuous　in　the　sense　in　which　the　process　of　thinking　is　so；　and　thinking　is　identical　with　the　thoughts　which　are　its　parts；　these　have　a　serial　unity　like　that　of　number；　not　a　unity　like　that　of　a　spatial　magnitude。　Hence　mind　cannot　have　that　kind　of　unity　either；　mind　is　either　without　parts　or　is　continuous　in　some　other　way　than　that　which　characterizes　a　spatial　magnitude。　How；　indeed；　if　it　were　a　spatial　magnitude；　could　mind　possibly　think？　Will　it　think　with　any　one　indifferently　of　its　parts？　In　this　case；　the　'part'　must　be　understood　either　in　the　sense　of　a　spatial　magnitude　or　in　the　sense　of　a　point　（if　a　point　can　be　called　a　part　of　a　spatial　magnitude）。　If　we　accept　the　latter　alternative；　the　points　being　infinite　in　number；　obviously　the　mind　can　never　exhaustively　traverse　them；　if　the　former；　the　mind　must　think　the　same　thing　over　and　over　again；　indeed　an　infinite　number　of　times　（whereas　it　is　manifestly　possible　to　think　a　thing　once　only）。　If　contact　of　any　part　whatsoever　of　itself　with　the　object　is　all　that　is　required；　why　need　mind　move　in　a　circle；　or　indeed　possess　magnitude　at　all？　On　the　other　hand；　if　contact　with　the　whole　circle　is　necessary；　what　meaning　can　be　given　to　the　contact　of　the　parts？　Further；　how　could　what　has　no　parts　think　what　has　parts；　or　what　has　parts　think　what　has　none？　We　must　identify　the　circle　referred　to　with　mind；　for　it　is　mind　whose　movement　is　thinking；　and　it　is　the　circle　whose　movement　is　revolution；　so　that　if　thinking　is　a　movement　of　revolution；　the　circle　which　has　this　characteristic　movement　must　be　mind。　　　If　the　circular　movement　is　eternal；　there　must　be　something　which　mind　is　always　thinking…what　can　this　be？　For　all　practical　processes　of　thinking　have　limits…they　al