a　reality　prior　to　its　attribution；　it　is　incumbent　upon　us　to　discover　the　intrinsic　nature　of　this　reality。　We　must　never　be　content　to　regard　as　a　relative　something　which　exists　prior　to　its　attribution；　but　only　that　which　is　engendered　by　Relation　and　has　no　existence　apart　from　the　relation　to　which　it　owes　its　name：　the　double；　strictly　so　called；　takes　birth　and　actuality　in　juxtaposition　with　a　yard's　length；　and　by　this　very　process　of　being　juxtaposed　with　a　correlative　acquires　the　name　and　exhibits　the　fact　of　being　double。　　　　　What；　then；　is　that　entity；　called　Motion；　which；　though　attributive；　has　an　independent　reality；　which　makes　its　attribution　possible…　the　entity　corresponding　to　Quality；　Quantity　and　Substance？　　　　　But　first；　perhaps；　we　should　make　sure　that　there　is　nothing　prior　to　Motion　and　predicated　of　it　as　its　genus。　　　　　Change　may　be　suggested　as　a　prior。　But；　in　the　first　place；　either　it　is　identical　with　Motion；　or　else；　if　change　be　claimed　as　a　genus；　it　will　stand　distinct　from　the　genera　so　far　considered：　secondly；　Motion　will　evidently　take　rank　as　a　species　and　have　some　other　species　opposed　to　it…　becoming；　say…　which　will　be　regarded　as　a　change　but　not　as　a　motion。　　　　　What；　then；　is　the　ground　for　denying　that　becoming　is　a　motion？　The　fact；　perhaps；　that　what　comes　to　be　does　not　yet　exist；　whereas　Motion　has　no　dealings　with　the　non…existent。　But；　on　that　ground；　becoming　will　not　be　a　change　either。　If　however　it　be　alleged　that　becoming　is　merely　a　type　of　alteration　or　growth　since　it　takes　place　when　things　alter　and　grow；　the　antecedents　of　becoming　are　being　confused　with　becoming　itself。　Yet　becoming；　entailing　as　it　does　these　antecedents；　must　necessarily　be　a　distinct　species；　for　the　event　and　process　of　becoming　cannot　be　identified　with　merely　passive　alteration；　like　turning　hot　or　white：　it　is　possible　for　the　antecedents　to　take　place　without　becoming　as　such　being　accomplished；　except　in　so　far　as　the　actual　alteration　＇implied　in　the　antecedents＇　has　〃come　to　be〃；　where；　however；　an　animal　or　a　vegetal　life　is　concerned；　becoming　＇or　birth＇　takes　place　only　upon　its　acquisition　of　a　Form。　　　　　The　contrary　might　be　maintained：　that　change　is　more　plausibly　ranked　as　a　species　than　is　Motion；　because　change　signifies　merely　the　substitution　of　one　thing　for　another；　whereas　Motion　involves　also　the　removal　of　a　thing　from　the　place　to　which　it　belongs；　as　is　shown　by　locomotion。　Even　rejecting　this　distinction；　we　must　accept　as　types　of　Motion　knowledge　and　musical　performance…　in　short；　changes　of　condition：　thus；　alteration　will　come　to　be　regarded　as　a　species　of　Motion…　namely；　motion　displacing。　　　　　22。　But　suppose　that　we　identify　alteration　with　Motion　on　the　ground　that　Motion　itself　results　in　difference：　how　then　do　we　proceed　to　define　Motion？　　　　　It　may　roughly　be　characterized　as　the　passage　from　the　potentiality　to　its　realization。　That　is　potential　which　can　either　pass　into　a　Form…　for　example；　the　potential　statue…　or　else　pass　into　actuality…　such　as　the　ability　to　walk：　whenever　progress　is　made　towards　the　statue；　this　progress　is　Motion；　and　when　the　ability　to　walk　is　actualized　in　walking；　this　walking　is　itself　Motion：　dancing　is；　similarly；　the　motion　produced　by　the　potential　dancer　taking　his　steps。　　　　　In　the　one　type　of　Motion　a　new　Form　comes　into　existence　created　by　the　motion；　the　other　constitutes；　as　it　were；　the　pure　Form　of　the　potentiality；　and　leaves　nothing　behind　it　when　once　the　motion　has　ceased。　Accordingly；　the　view　would　not　be　unreasonable　which；　taking　some　Forms　to　be　active；　others　inactive；　regarded　Motion　as　a　dynamic　Form　in　opposition　to　the　other　Forms　which　are　static；　and　further　as　the　cause　of　whatever　new　Form　ensues　upon　it。　To　proceed　to　identify　this　bodily　motion　with　life　would　however　be　unwarrantable；　it　must　be　considered　as　identical　only　in　name　with　the　motions　of　Intellect　and　Soul。　　　　　That　Motion　is　a　genus　we　may　be　all　the　more　confident　in　virtue　of　the　difficulty…　the　impossibility　even…　of　confining　it　within　a　definition。　　　　　But　how　can　it　be　a　Form　in　cases　where　the　motion　leads　to　deterioration；　or　is　purely　passive？　Motion；　we　may　suggest；　is　like　the　heat　of　the　sun　causing　some　things　to　grow　and　withering　others。　In　so　far　as　Motion　is　a　common　property；　it　is　identical　in　both　conditions；　its　apparent　difference　is　due　to　the　objects　moved。　　　　　Is；　then；　becoming　ill　identical　with　becoming　well？　As　motions　they　are　identical。　In　what　respect；　then；　do　they　differ？　In　their　substrates？　or　is　there　some　other　criterion？　　　　　This　question　may　however　be　postponed　until　we　come　to　consider　alteration：　at　present　we　have　to　discover　what　is　the　constant　element　in　every　motion；　for　only　on　this　basis　can　we　establish　the　claim　of　Motion　to　be　a　genus。　　　　　Perhaps　the　one　term　covers　many　meanings；　its　claim　to　generic　status　would　then　correspond　to　that　of　Being。　　　　　As　a　solution　of　the　problem　we　may　suggest　that　motions　conducing　to　the　natural　state　or　functioning　in　natural　conditions　should　perhaps；　as　we　have　already　asserted；　be　regarded　as　being　in　a　sense　Forms；　while　those　whose　direction　is　contrary　to　nature　must　be　supposed　to　be　assimilated　to　the　results　towards　which　they　lead。　　　　　But　what　is　the　constant　element　in　alteration；　in　growth　and　birth　and　their　opposites；　in　local　change？　What　is　that　which　makes　them　all　motions？　Surely　it　is　the　fact　that　in　every　case　the　object　is　never　in　the　same　state　before　and　after　the　motion；　that　it　cannot　remain　still　and　in　complete　inactivity　but；　so　long　as　the　motion　is　present；　is　continually　urged　to　take　a　new　condition；　never　acquiescing　in　Identity　but　always　courting　Difference；　deprived　of　Difference；　Motion　perishes。　　　　　Thus；　Difference　may　be　predicated　of　Motion；　not　merely　in　the　sense　that　it　arises　and　persists　in　a　difference　of　conditions；　but　in　the　sense　of　being　itself　perpetual　difference。　It　follows　that　Time；　as　being　created　by　Motion；　also　entails　perpetual　difference：　Time　is　the　measure　of　unceasing　Motion；　accompanying　its　course　and；　as　it　were；　carried　along　its　stream。　　　　　In　short；　the　common　basis　of　all　Motion　is　the　existence　of　a　progression　and　an　urge　from　potentiality　and　the　potential　to　actuality　and　the　actual：　everything　which　has　any　kind　of　motion　whatsoever　derives　this　motion　from　a　pre…existent　potentiality　within　itself　of　activity　or　passivity。　　　　　23。　The　Motion　which　acts　upon　Sensible　objects　enters　from　without；　and　so　shakes；　drives；　rouses　and　thrusts　its　participants　that　they　may　neither　rest　nor　preserve　their　identity…　and　all　to　the　end　that　they　may　be　caught　into　that　restlessness；　that　flustering　excitability　which　is　but　an　image　of　Life。　　　　　We　must　avoid　identifying　Motion　with　the　objects　moved：　by　walking　we　do　not　mean　the　feet　but　the　activity　springing　from　a　potentiality　in　the　feet。　Since　the　potentiality　is　invisible；　we　see　of　necessity　only　the　active　feet…　that　is　to　say；　not　feet　simply；　as　would　be　the　case　if　they　were　at　rest；　but　something　besides　feet；　something　invisible　but　indirectly　seen　as　an　accompaniment　by　the　fact　that　we　observe　the　feet　to　be　in　ever…changing　positions　and　no　longer　at　rest。　We　infer　alteration；　on　the　other　hand；　from　the　qualitative　change　in　the　thing　altered。　　　　　Where；　then；　does　Motion　reside；　when　there　is　one　thing　that　moves　and　another　that　passes　from　an　inherent　potentiality　to　actuality？　In　the　mover？　How　then　will　the　moved；　the　patient；　participate　in　the　motion？　In　the　moved？　Then　why　does　not　Motion　remain　in　it；　once　having　come？　It　would　seem　that　Motion　must　neither　be　separated　from　the　active　principle　nor　allowed　to　reside　in　it；　it　must　proceed　from　agent　to　patient　without　so　inhering　in　the　latter　as　to　be　severed　from　the　former；　passing　from　one　to　the　other　like　a　breath　of　wind。　　　　　Now；　when　the　potentiality　of　Motion　consists　in　an　ability　to　walk；　it　may　be　imagined　as　thrusting　a　man　forward　and　causing　him　to　be　continually　adopting　a　different　position；　when　it　lies　in　the　capacity　to　heat；　it　heats；　when　the　potentiality　takes　hold　of　Matter　and　builds　up　the　organism；　we　have　growth；　and　when　another　potentiality　demolishes　the　structure；　the　result　is　decay；　that　which　has　the　potentiality　of　demolition　experiencing　the　decay。　Where　the　birth…giving　principle　is　active；　we　find　birth；　where　it　is　impotent　and　the　power　to　destroy　prevails；　destruction　takes　place…　not　the　destruction　of　what　already　exists；　but　that　which　intervenes　upon　the　road　to　existence。　　　　　Health　comes　about　in　the　same　way…　when　the　power　which　produces　health　is　active　and　predominant；　sickness　is　the　result　of　the　opposite　power　working　in　the　opposite　direction。　　　　　Thus；　Motion　is　conditioned；　not　only　by　the　objects　in　which　it　occurs；　but　also　by　its　origins　and　its　course；　and　it　is　a　distinctive　mark　of　Motion　to　be　always　qualified　and　to　take　its　quality　from　the　moved。　　　　　24。　With　regard　to　locomotion：　if　ascending　is　to　be　held　contrary　to　descending；　and　circular　motion　different　＇in　kind＇　from　motion　in　a　straight　line；　we　may　ask　how　this　difference　is　to　be　defined…　the　difference；　f