on the motion of animals-第4章

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its　elbow…joint　would　be　situate　the　original　seat　of　the　moving　soul。



Since；　however；　it　is　possible　for　a　lifeless　thing　to　be　so　related



to　the　hand　as　the　forearm　is　to　the　upper　（for　example；　when　a　man



moves　a　stick　in　his　hand）；　it　is　evident　that　the　soul；　the



original　of　movement；　could　not　lie　in　either　of　the　two　extreme



points；　neither；　that　is；　in　the　last　point　of　the　stick　which　is



moved；　nor　in　the　original　point　which　causes　movement。　For　the



stick　too　has　an　end　point　and　an　originative　point　by　reference　to



the　hand。　Accordingly；　this　example　shows　that　the　moving　original



which　derives　from　the　soul　is　not　in　the　stick　and　if　not；　then　not



in　the　hand；　for　a　precisely　similar　relation　obtains　between　the　hand



and　the　wrist；　as　between　the　wrist　and　the　elbow。　In　this　matter　it



makes　no　difference　whether　the　part　is　a　continuous　part　of　the



body　or　not；　the　stick　may　be　looked　at　as　a　detached　part　of　the



whole。　It　follows　then　of　necessity　that　the　original　cannot　lie　in



any　individual　origin　which　is　the　end　of　another　member；　even



though　there　may　lie　another　part　outside　the　one　in　question。　For



example；　relatively　to　the　end　point　of　the　stick　the　hand　is　the



original；　but　the　original　of　the　hand's　movement　is　in　the　wrist。　And



so　if　the　true　original　is　not　in　the　hand；　be…there　is　still



something　higher　up；　neither　is　the　true　original　in　the　wrist；　for



once　more　if　the　elbow　is　at　rest　the　whole　part　below　it　can　be　moved



as　a　continuous　whole。



　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　9







　　Now　since　the　left　and　the　right　sides　are　symmetrical；　and　these



opposites　are　moved　simultaneously；　it　cannot　be　that　the　left　is



moved　by　the　right　remaining　stationary；　nor　vice　versa；　the



original　must　always　be　in　what　lies　above　both。　Therefore；　the



original　seat　of　the　moving　soul　must　be　in　that　which　lies　in　the



middle；　for　of　both　extremes　the　middle　is　the　limiting　point；　and



this　is　similarly　related　to　the　movements　from　above　＇and　below；＇



those　that　is　from　the　head；　and　to　the　bones　which　spring　from　the



spinal　column；　in　creatures　that　have　a　spinal　column。



　　And　this　is　a　reasonable　arrangement。　For　the　sensorium　is　in　our



opinion　in　the　centre　too；　and　so；　if　the　region　of　the　original　of



movement　is　altered　in　structure　through　sense…perception　and　thus



changes；　it　carries　with　it　the　parts　that　depend　upon　it　and　they　too



are　extended　or　contracted；　and　in　this　way　the　movement　of　the



creature　necessarily　follows。　And　the　middle　of　the　body　must　needs　be



in　potency　one　but　in　action　more　than　one；　for　the　limbs　are　moved



simultaneously　from　the　original　seat　of　movement；　and　when　one　is



at　rest　the　other　is　moved。　For　example；　in　the　line　BAC；　B　is



moved；　and　A　is　the　mover。　There　must；　however；　be　a　point　at　rest



if　one　is　to　move；　the　other　to　be　moved。　A　（AE）　then　being　one　in



potency　must　be　two　in　action；　and　so　be　a　definite　spatial



magnitude　not　a　mathematical　point。　Again；　C　may　be　moved



simultaneously　with　B。　Both　the　originals　then　in　A　must　move　and



be；　and　so　there　must　be　something　other　than　them　which　moves　but



is　not　moved。　For　otherwise；　when　the　movement　begins；　the　extremes；



i。e。　the　originals；　in　A　would　rest　upon　one　another；　like　two　men



putting　themselves　back　to　back　and　so　moving　their　legs。　There　must



then　be　some　one　thing　which　moves　both。　This　something　is　the　soul；



distinct　from　the　spatial　magnitude　just　described　and　yet　located



therein。



　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　10







　　Although　from　the　point　of　view　of　the　definition　of　movement…　a



definition　which　gives　the　cause…　desire　is　the　middle　term　or



cause；　and　desire　moves　being　moved；　still　in　the　material　animated



body　there　must　be　some　material　which　itself　moves　being　moved。　Now



that　which　is　moved；　but　whose　nature　is　not　to　initiate　movement；



is　capable　of　being　passive　to　an　external　force；　while　that　which



initiates　movement　must　needs　possess　a　kind　of　force　and　power。　Now



experience　shows　us　that　animals　do　both　possess　connatural　spirit　and



derive　power　from　this。　（How　this　connatural　spirit　is　maintained　in



the　body　is　explained　in　other　passages　of　our　works。）　And　this　spirit



appears　to　stand　to　the　soul…centre　or　original　in　a　relation



analogous　to　that　between　the　point　in　a　joint　which　moves　being　moved



and　the　unmoved。　Now　since　this　centre　is　for　some　animals　in　the



heart；　in　the　rest　in　a　part　analogous　with　the　heart；　we　further



see　the　reason　for　the　connatural　spirit　being　situate　where　it



actually　is　found。　The　question　whether　the　spirit　remains　always



the　same　or　constantly　changes　and　is　renewed；　like　the　cognate



question　about　the　rest　of　the　parts　of　the　body；　is　better　postponed。



At　all　events　we　see　that　it　is　well　disposed　to　excite　movement　and



to　exert　power；　and　the　functions　of　movement　are　thrusting　and



pulling。　Accordingly；　the　organ　of　movement　must　be　capable　of



expanding　and　contracting；　and　this　is　precisely　the　characteristic　of



spirit。　It　contracts　and　expands　naturally；　and　so　is　able　to　pull　and



to　thrust　from　one　and　the　same　cause；　exhibiting　gravity　compared



with　the　fiery　element；　and　levity　by　comparison　with　the　opposites　of



fire。　Now　that　which　is　to　initiate　movement　without　change　of



structure　must　be　of　the　kind　described；　for　the　elementary　bodies



prevail　over　one　another　in　a　compound　body　by　dint　of



disproportion；　the　light　is　overcome　and　kept　down　by　the　heavier；　and



the　heavy　kept　up　by　the　lighter。



　　We　have　now　explained　what　the　part　is　which　is　moved　when　the



soul　originates　movement　in　the　body；　and　what　is　the　reason　for　this。



And　the　animal　organism　must　be　conceived　after　the　similitude　of　a



well…governed　commonwealth。　When　order　is　once　established　in　it　there



is　no　more　need　of　a　separate　monarch　to　preside　over　each　several



task。　The　individuals　each　play　their　assigned　part　as　it　is



ordered；　and　one　thing　follows　another　in　its　accustomed　order。　So



in　animals　there　is　the　same　orderliness…　nature　taking　the　place　of



custom…　and　each　part　naturally　doing　his　own　work　as　nature　has



composed　them。　There　is　no　need　then　of　a　soul　in　each　part；　but　she



resides　in　a　kind　of　central　governing　place　of　the　body；　and　the



remaining　parts　live　by　continuity　of　natural　structure；　and　play



the　parts　Nature　would　have　them　play。



　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　11







　　So　much　then　for　the　voluntary　movements　of　animal　bodies；　and　the



reasons　for　them。　These　bodies；　however；　display　in　certain　members



involuntary　movements　too；　but　most　often　non…voluntary　movements。



By　involuntary　I　mean　motions　of　the　heart　and　of　the　privy　member；



for　often　upon　an　image　arising　and　without　express　mandate　of　the



reason　these　parts　are　moved。　By　non…voluntary　I　mean　sleep　and　waking



and　respiration；　and　other　similar　organic　movements。　For　neither



imagination　nor　desire　is　properly　mistress　of　any　of　these；　but　since



the　animal　body　must　undergo　natural　changes　of　quality；　and　when



the　parts　are　so　altered　some　must　increase　and　other　decrease；　the



body　must　straightway　be　moved　and　change　with　the　changes　that　nature



makes　dependent　upon　one　another。　Now　the　causes　of　the　movements



are　natural　changes　of　temperature；　both　those　coming　from　outside　the



body；　and　those　taking　place　within　it。　So　the　involuntary　movements



which　occur　in　spite　of　reason　in　the　aforesaid　parts　occur　when　a



change　of　quality　supervenes。　For　conception　and　imagination；　as　we



said　above；　produce　the　conditions　necessary　to　affections；　since　they



bring　to　bear　the　images　or　forms　which　tend　to　create　these　states。



And　the　two　parts　aforesaid　display　this　motion　more　conspicuously



than　the　rest；　because　each　is　i