on the motion of animals-第3部分

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change　of　quality　is　caused　by　imaginations　and　sensations　and　by



ideas。　Sensations　are　obviously　a　form　of　change　of　quality；　and



imagination　and　conception　have　the　same　effect　as　the　objects　so



imagined　and　conceived　For　in　a　measure　the　form　conceived　be　it　of



hot　or　cold　or　pleasant　or　fearful　is　like　what　the　actual　objects



would　be；　and　so　we　shudder　and　are　frightened　at　a　mere　idea。　Now　all



these　affections　involve　changes　of　quality；　and　with　those　changes



some　parts　of　the　body　enlarge；　others　grow　smaller。　And　it　is　not



hard　to　see　that　a　small　change　occurring　at　the　centre　makes　great



and　numerous　changes　at　the　circumference；　just　as　by　shifting　the



rudder　a　hair's　breadth　you　get　a　wide　deviation　at　the　prow。　And



further；　when　by　reason　of　heat　or　cold　or　some　kindred　affection　a



change　is　set　up　in　the　region　of　the　heart；　even　in　an



imperceptibly　small　part　of　the　heart；　it　produces　a　vast　difference



in　the　periphery　of　the　body；…　blushing；　let　us　say；　or　turning　white；



goose…skin　and　shivers　and　their　opposites。



　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　8







　　But　to　return；　the　object　we　pursue　or　avoid　in　the　field　of



action　is；　as　has　been　explained；　the　original　of　movement；　and　upon



the　conception　and　imagination　of　this　there　necessarily　follows　a



change　in　the　temperature　of　the　body。　For　what　is　painful　we　avoid；



what　is　pleasing　we　pursue。　We　are；　however；　unconscious　of　what



happens　in　the　minute　parts；　still　anything　painful　or　pleasing　is



generally　speaking　accompanied　by　a　definite　change　of　temperature



in　the　body。　One　may　see　this　by　considering　the　affections。　Blind



courage　and　panic　fears；　erotic　motions；　and　the　rest　of　the　corporeal



affections；　pleasant　and　painful；　are　all　accompanied　by　a　change　of



temperature；　some　in　a　particular　member；　others　in　the　body



generally。　So；　memories　and　anticipations；　using　as　it　were　the



reflected　images　of　these　pleasures　and　pains；　are　now　more　and　now



less　causes　of　the　same　changes　of　temperature。　And　so　we　see　the



reason　of　nature's　handiwork　in　the　inward　parts；　and　in　the　centres



of　movement　of　the　organic　members；　they　change　from　solid　to　moist；



and　from　moist　to　solid；　from　soft　to　hard　and　vice　versa。　And　so　when



these　are　affected　in　this　way；　and　when　besides　the　passive　and



active　have　the　constitution　we　have　many　times　described；　as　often　as



it　comes　to　pass　that　one　is　active　and　the　other　passive；　and　neither



of　them　falls　short　of　the　elements　of　its　essence；　straightway　one



acts　and　the　other　responds。　And　on　this　account　thinking　that　one



ought　to　go　and　going　are　virtually　simultaneous；　unless　there　be



something　else　to　hinder　action。　The　organic　parts　are　suitably



prepared　by　the　affections；　these　again　by　desire；　and　desire　by



imagination。　Imagination　in　its　turn　depends　either　upon　conception　or



sense…perception。　And　the　simultaneity　and　speed　are　due　to　the



natural　correspondence　of　the　active　and　passive。



　　However；　that　which　first　moves　the　animal　organism　must　be



situate　in　a　definite　original。　Now　we　have　said　that　a　joint　is　the



beginning　of　one　part　of　a　limb；　the　end　of　another。　And　so　nature



employs　it　sometimes　as　one；　sometimes　as　two。　When　movement　arises



from　a　joint；　one　of　the　extreme　points　must　remain　at　rest；　and　the



other　be　moved　（for　as　we　explained　above　the　mover　must　support



itself　against　a　point　at　rest）；　accordingly；　in　the　case　of　the



elbow…joint；　the　last　point　of　the　forearm　is　moved　but　does　not



move　anything；　while；　in　the　flexion；　one　point　of　the　elbow；　which



lies　in　the　whole　forearm　that　is　being　moved；　is　moved；　but　there



must　also　be　a　point　which　is　unmoved；　and　this　is　our　meaning　when　we



speak　of　a　point　which　is　in　potency　one；　but　which　becomes　two　in



actual　exercise。　Now　if　the　arm　were　the　living　animal；　somewhere　in



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