Ingeneral，itisabsurdtomakethefactthatthethingsof
　　thisearthareobservedtochangeandnevertoremaininthesame
　　state，thebasisofourjudgementaboutthetruth。Forinpursuingthe
　　truthonemuststartfromthethingsthatarealwaysinthesamestate
　　andsuffernochange。Sucharetheheavenlybodies；forthesedonot
　　appeartobenowofonenatureandagainofanother，butare
　　manifestlyalwaysthesameandshareinnochange。
　　Further，ifthereismovement，thereisalsosomethingmoved，
　　andeverythingismovedoutofsomethingandintosomething；it
　　followsthatthatthatwhichismovedmustfirstbeinthatoutof
　　whichitistobemoved，andthennotbeinit，andmoveintothe
　　otherandcometobeinit，andthatthecontradictorystatements
　　arenottrueatthesametime，asthesethinkersasserttheyare。
　　Andifthethingsofthisearthcontinuouslyflowandmovein
　　respectofquantity-ifoneweretosupposethis，althoughitisnot
　　true-whyshouldtheynotendureinrespectofquality？Forthe
　　assertionofcontradictorystatementsaboutthesamethingseemsto
　　havearisenlargelyfromthebeliefthatthequantityofbodiesdoes
　　notendure，which，ouropponentshold，justifiestheminsayingthat
　　thesamethingbothisandisnotfourcubitslong。Butessence
　　dependsonquality，andthisisofdeterminatenature，thoughquantity
　　isofindeterminate。
　　Further，whenthedoctororderspeopletotakesomeparticular
　　food，whydotheytakeit？Inwhatrespectis’thisisbread’truer
　　than’thisisnotbread’？Andsoitwouldmakenodifferencewhether
　　oneateornot。Butasamatteroffacttheytakethefoodwhichis
　　ordered，assumingthattheyknowthetruthaboutitandthatitis
　　bread。Yettheyshouldnot，iftherewerenofixedconstantnature
　　insensiblethings，butallnaturesmovedandflowedforever。
　　Again，ifwearealwayschangingandneverremainthesame，what
　　wonderisitiftous，astothesick，thingsneverappearthesame？
　　Fortothemalso，becausetheyarenotinthesameconditionas
　　whentheywerewell，sensiblequalitiesdonotappearalike；yet，
　　forallthat，thesensiblethingsthemselvesneednotshareinany
　　change，thoughtheyproducedifferent，andnotidentical，sensations
　　inthesick。Andthesamemustsurelyhappentothehealthyifthe
　　afore-saidchangetakesplace。Butifwedonotchangebutremainthe
　　same，therewillbesomethingthatendures。
　　Asforthosetowhomthedifficultiesmentionedaresuggestedby
　　reasoning，itisnoteasytosolvethedifficultiestotheir
　　satisfaction，unlesstheywillpositsomethingandnolongerdemand
　　areasonforit；foritisonlythusthatallreasoningandall
　　proofisaccomplished；iftheypositnothing，theydestroy
　　discussionandallreasoning。Thereforewithsuchmenthereisno
　　reasoning。Butasforthosewhoareperplexedbythetraditional
　　difficulties，itiseasytomeetthemandtodissipatethecausesof
　　theirperplexity。Thisisevidentfromwhathasbeensaid。
　　Itismanifest，therefore，fromtheseargumentsthatcontradictory
　　statementscannotbetrulymadeaboutthesamesubjectatonetime，
　　norcancontrarystatements，becauseeverycontrarietydependson
　　privation。Thisisevidentifwereducethedefinitionsof
　　contrariestotheirprinciple。
　　Similarly，nointermediatebetweencontrariescanbepredicatedof
　　oneandthesamesubject，ofwhichoneofthecontrariesis
　　predicated。Ifthesubjectiswhiteweshallbewronginsayingit
　　isneitherblacknorwhite，forthenitfollowsthatitisandis
　　notwhite；forthesecondofthetwotermswehaveputtogetheris
　　trueofit，andthisisthecontradictoryofwhite。
　　Wecouldnotberight，then，inacceptingtheviewseitherof
　　HeraclitusorofAnaxagoras。Ifwewere，itwouldfollowthat
　　contrarieswouldbepredicatedofthesamesubject；forwhen
　　Anaxagorassaysthatineverythingthereisapartofeverything，he
　　saysnothingissweetanymorethanitisbitter，andsowithany
　　otherpairofcontraries，sinceineverythingeverythingispresent
　　notpotentiallyonly，butactuallyandseparately。Andsimilarlyall
　　statementscannotbefalsenoralltrue，bothbecauseofmanyother
　　difficultieswhichmightbeadducedasarisingfromthisposition，and
　　becauseifallarefalseitwillnotbetruetosayeventhis，and
　　ifallaretrueitwillnotbefalsetosayallarefalse。
　　Everyscienceseekscertainprinciplesandcausesforeachof
　　itsobjects-e。g。medicineandgymnasticsandeachoftheother
　　sciences，whetherproductiveormathematical。Foreachofthese
　　marksoffacertainclassofthingsforitselfandbusiesitselfabout
　　thisasaboutsomethingexistingandreal，-nothoweverquareal；the
　　sciencethatdoesthisisanotherdistinctfromthese。Ofthesciences
　　mentionedeachgetssomehowthe’what’insomeclassofthingsand
　　triestoprovetheothertruths，withmoreorlessprecision。Someget
　　the’what’throughperception，othersbyhypothesis；sothatitis
　　clearfromaninductionofthissortthatthereisnodemonstration。
　　ofthesubstanceor’what’。
　　Thereisascienceofnature，andevidentlyitmustbedifferent
　　bothfrompracticalandfromproductivescience。Forinthecaseof
　　productivesciencetheprincipleofmovementisintheproducerand
　　notintheproduct，andiseitheranartorsomeotherfaculty。And
　　similarlyinpracticalsciencethemovementisnotinthething
　　done，butratherinthedoers。Butthescienceofthenatural
　　philosopherdealswiththethingsthathaveinthemselvesa
　　principleofmovement。Itisclearfromthesefacts，then，that
　　naturalsciencemustbeneitherpracticalnorproductive，but
　　theoreticalforitmustfallintosomeoneoftheseclasses。And
　　sinceeachofthesciencesmustsomehowknowthe’what’andusethis
　　asaprinciple，wemustnotfalltoobservehowthenatural
　　philosophershoulddefinethingsandhowheshouldstatethe
　　definitionoftheessence-whetherasakinto’snub’orratherto
　　’concave’。Forofthesethedefinitionof’snub’includesthematter
　　ofthething，butthatof’concave’isindependentofthematter；
　　forsnubnessisfoundinanose，sothatwelookforitsdefinition
　　withouteliminatingthenose，forwhatissnubisaconcavenose。
　　Evidentlythenthedefinitionoffleshalsoandoftheeyeandof
　　theotherpartsmustalwaysbestatedwithouteliminatingthematter。
　　Sincethereisascienceofbeingquabeingandcapableof
　　existingapart，wemustconsiderwhetherthisistoberegardedasthe
　　sameasphysicsorratherasdifferent。Physicsdealswiththe
　　thingsthathaveaprincipleofmovementinthemselves；mathematicsis
　　theoretical，andisasciencethatdealswiththingsthatareatrest，
　　butitssubjectscannotexistapart。Thereforeaboutthatwhichcan
　　existapartandisunmovablethereisasciencedifferentfrombothof
　　these，ifthereisasubstanceofthisnatureImeanseparableand
　　unmovable，asweshalltrytoprovethereis。Andifthereissuch
　　akindofthingintheworld，heremustsurelybethedivine，andthis
　　mustbethefirstandmostdominantprinciple。Evidently，then，
　　therearethreekindsoftheoreticalsciences-physics，mathematics，
　　theology。Theclassoftheoreticalsciencesisthebest，andof
　　thesethemselvesthelastnamedisbest；foritdealswiththehighest
　　ofexistingthings，andeachscienceiscalledbetterorworsein
　　virtueofitsproperobject。
　　Onemightraisethequestionwhetherthescienceofbeingqua
　　beingistoberegardedasuniversalornot。Eachofthe
　　mathematicalsciencesdealswithsomeonedeterminateclassofthings，
　　butuniversalmathematicsappliesaliketoall。Nowifnatural
　　substancesarethefirstofexistingthings，physicsmustbethefirst
　　ofsciences；butifthereisanotherentityandsubstance，separable
　　andunmovable，theknowledgeofitmustbedifferentandpriorto
　　physicsanduniversalbecauseitisprior。
　　Since’being’ingeneralhasseveralsenses，ofwhichoneis
　　’beingbyaccident’，wemustconsiderfirstthatwhich’is’inthis
　　sense。Evidentlynoneofthetraditionalsciencesbusiesitself
　　abouttheaccidental。Forneitherdoesarchitectureconsiderwhatwill
　　happentothosewhoaretousethehousee。g。whethertheyhavea
　　painfullifeinitornot，nordoesweaving，orshoemaking，orthe
　　confectioner’sart，dothelike；buteachofthesesciences
　　considersonlywhatispeculiartoit，i。e。itsproperend。Andasfor
　　theargumentthat’whenhewhoismusicalbecomesletteredhe’llbe
　　bothatonce，nothavingbeenbothbefore；andthatwhichis，not
　　alwayshavingbeen，musthavecometobe；thereforehemusthaveat
　　oncebecomemusicalandlettered’，-thisnoneoftherecognized
　　sciencesconsiders，butonlysophistic；forthisalonebusiesitself
　　abouttheaccidental，sothatPlatoisnotfarwrongwhenhesaysthat
　　thesophistspendshistimeonnon-being。
　　Thatascienceoftheaccidentalisnotevenpossiblewillbe
　　evidentifwetrytoseewhattheaccidentalreallyis。Wesaythat
　　everythingeitherisalwaysandofnecessitynecessitynotinthe
　　senseofviolence，butthatwhichweappealtoindemonstrations，
　　orisforthemostpart，orisneitherforthemostpart，noralways
　　andofnecessity，butmerelyasitchances；e。g。theremightbecold
　　inthedogdays，butthisoccursneitheralwaysandofnecessity，nor
　　forthemostpart，thoughitmighthappensometimes。Theaccidental，
　　then，iswhatoccurs，butnotalwaysnorofnecessity，norforthe
　　mostpart。Nowwehavesaidwhattheaccidentalis，anditis
　　obviouswhythereisnoscienceofsuchathing；forallscienceisof
　　thatwhichisalwaysorforthemostpart，buttheaccidentalisin
　　neitheroftheseclasses。
　　Evidentlytherearenotcausesandprinciplesoftheaccidental，
　　ofthesamekindasthereareoftheessential；foriftherewere，
　　everythingwouldbeofnecessity。IfAiswhenBis，andBiswhenC
　　is，andifCexistsnotbychancebutofnecessity，thatalsoofwhich
　　Cwascausewillexistofnecessity，downtothelastcausatumasit
　　iscalledbutthiswassupposedtobeaccidental。Thereforeall
　　thingswillbeofnecessity，andchanceandthepossibilityofa
　　thing’seitheroccurringornotoccurringareremovedentirelyfrom
　　therangeofevents。Andifthecausebesupposednottoexistbut
　　tobecomingtobe，thesameresultswillfollow；everythingwill
　　occurofnecessity。Forto-morrow’seclipsewilloccurifAoccurs，
　　andAifBoccurs，andBifCoccurs；andinthiswayifwesubtract
　　timefromthelimitedtimebetweennowandto-morrowweshallcome
　　sometimetothealreadyexistingcondition。Thereforesincethis
　　exists，everythingafterthiswilloccurofnecessity，sothatall
　　thingsoccurofnecessity。
　　Astothatwhich’is’inthesenseofbeingtrueorofbeingby
　　accident，theformerdependsonacombinationinthoughtandisan
　　affectionofthoughtwhichisthereasonwhyitistheprinciples，
　　notofthatwhich’is’inthissense，butofthatwhichisoutsideand
　　canexistapart，thataresought；andthelatterisnotnecessarybut
　　indeterminateImeantheaccidental；andofsuchathingthe
　　causesareunorderedandindefinite。
　　Adaptationtoanendisfoundineventsthathappenbynatureor
　　astheresultofthought。Itis’luck’whenoneoftheseevents
　　happensbyaccident。Forasathingmayexist，soitmaybeacause，
　　eitherbyitsownnatureorbyaccident。Luckisanaccidentalcause
　　atworkinsucheventsadaptedtoanendasareusuallyeffectedin
　　accordancewithpurpose。Andsoluckandthoughtareconcernedwith
　　thesamesphere；forpurposecannotexistwithoutthought。The
　　causesfromwhichluckyresultsmighthappenareindeterminate；andso
　　luckisobscuretohumancalculationandisacausebyaccident，but
　　intheunqualifiedsenseacauseofnothing。Itisgoodorbadluck
　　whentheresultisgoodorevil；andprosperityormisfortunewhenthe
　　scaleoftheresultsislarge。
　　Sincenothingaccidentalispriortotheessential，neitherare
　　accidentalcausesprior。If，then，luckorspontaneityisacauseof
　　thematerialuniverse，reasonandnaturearecausesbeforeit。