havesightthattheymaysee。Andsimilarlymenhavetheartof
　　buildingthattheymaybuild，andtheoreticalsciencethattheymay
　　theorize；buttheydonottheorizethattheymayhavetheoretical
　　science，exceptthosewhoarelearningbypractice；andthesedonot
　　theorizeexceptinalimitedsense，orbecausetheyhavenoneedto
　　theorize。Further，matterexistsinapotentialstate，justbecauseit
　　maycometoitsform；andwhenitexistsactually，thenitisinits
　　form。Andthesameholdsgoodinallcases，eventhoseinwhichthe
　　endisamovement。Andso，asteachersthinktheyhaveachieved
　　theirendwhentheyhaveexhibitedthepupilatwork，naturedoes
　　likewise。Forifthisisnotthecase，weshallhavePauson’sHermes
　　overagain，sinceitwillbehardtosayabouttheknowledge，asabout
　　thefigureinthepicture，whetheritiswithinorwithout。Forthe
　　actionistheend，andtheactualityistheaction。Andsoeventhe
　　word’actuality’isderivedfrom’action’，andpointstothe
　　completereality。
　　Andwhileinsomecasestheexerciseistheultimatethinge。g。
　　insighttheultimatethingisseeing，andnootherproductbesides
　　thisresultsfromsight，butfromsomethingsaproductfollowse。g。
　　fromtheartofbuildingthereresultsahouseaswellastheactof
　　building，yetnonethelesstheactisintheformercasetheendand
　　inthelattermoreofanendthanthepotencyis。Fortheactof
　　buildingisrealizedinthethingthatisbeingbuilt，andcomesto
　　be，andis，atthesametimeasthehouse。
　　Where，then，theresultissomethingapartfromtheexercise，
　　theactualityisinthethingthatisbeingmade，e。g。theactof
　　buildingisinthethingthatisbeingbuiltandthatofweavingin
　　thethingthatisbeingwoven，andsimilarlyinallothercases，and
　　ingeneralthemovementisinthethingthatisbeingmoved；butwhere
　　thereisnoproductapartfromtheactuality，theactualityispresent
　　intheagents，e。g。theactofseeingisintheseeingsubjectand
　　thatoftheorizinginthetheorizingsubjectandthelifeisinthe
　　soulandthereforewell-beingalso；foritisacertainkindof
　　life。
　　Obviously，therefore，thesubstanceorformisactuality。
　　Accordingtothisargument，then，itisobviousthatactualityis
　　priorinsubstantialbeingtopotency；andaswehavesaid，one
　　actualityalwaysprecedesanotherintimerightbacktothe
　　actualityoftheeternalprimemover。
　　Butbactualityispriorinastrictersensealso；foreternal
　　thingsarepriorinsubstancetoperishablethings，andnoeternal
　　thingexistspotentially。Thereasonisthis。Everypotencyisat
　　oneandthesametimeapotencyoftheopposite；for，whilethatwhich
　　isnotcapableofbeingpresentinasubjectcannotbepresent，
　　everythingthatiscapableofbeingmaypossiblynotbeactual。
　　That，then，whichiscapableofbeingmayeitherbeornotbe；the
　　samething，then，iscapablebothofbeingandofnotbeing。And
　　thatwhichiscapableofnotbeingmaypossiblynotbe；andthatwhich
　　maypossiblynotbeisperishable，eitherinthefullsense，orinthe
　　precisesenseinwhichitissaidthatitpossiblymaynotbe，i。e。in
　　respecteitherofplaceorofquantityorquality；’inthefullsense’
　　means’inrespectofsubstance’。Nothing，then，whichisinthefull
　　senseimperishableisinthefullsensepotentiallyexistentthough
　　thereisnothingtopreventitsbeingsoinsomerespect，e。g。
　　potentiallyofacertainqualityorinacertainplace；all
　　imperishablethings，then，existactually。Norcananythingwhichis
　　ofnecessityexistpotentially；yetthesethingsareprimary；forif
　　thesedidnotexist，nothingwouldexist。Nordoeseternalmovement，
　　iftherebesuch，existpotentially；and，ifthereisaneternal
　　mobile，itisnotinmotioninvirtueofapotentiality，exceptin
　　respectof’whence’and’whither’thereisnothingtopreventits
　　havingmatterwhichmakesitcapableofmovementinvarious
　　directions。Andsothesunandthestarsandthewholeheavenare
　　everactive，andthereisnofearthattheymaysometimestand
　　still，asthenaturalphilosophersfeartheymay。Nordotheytire
　　inthisactivity；formovementisnotforthem，asitisfor
　　perishablethings，connectedwiththepotentialityforopposites，so
　　thatthecontinuityofthemovementshouldbelaborious；foritis
　　thatkindofsubstancewhichismatterandpotency，notactuality，
　　thatcausesthis。
　　Imperishablethingsareimitatedbythosethatareinvolvedin
　　change，e。g。earthandfire。Forthesealsoareeveractive；for
　　theyhavetheirmovementofthemselvesandinthemselves。Butthe
　　otherpotencies，accordingtoourpreviousdiscussion，areall
　　potenciesforopposites；forthatwhichcanmoveanotherinthisway
　　canalsomoveitnotinthisway，i。e。ifitactsaccordingtoa
　　rationalformula；andthesamenon-rationalpotencieswillproduce
　　oppositeresultsbytheirpresenceorabsence。
　　If，then，thereareanyentitiesorsubstancessuchasthe
　　dialecticianssaytheIdeasare，theremustbesomethingmuchmore
　　scientificthanscience-itselfandsomethingmoremobilethan
　　movement-itself；forthesewillbemoreofthenatureof
　　actualities，whilescience-itselfandmovement-itselfarepotencies
　　forthese。
　　Obviously，then，actualityispriorbothtopotencyandtoevery
　　principleofchange。
　　Thattheactualityisalsobetterandmorevaluablethanthe
　　goodpotencyisevidentfromthefollowingargument。Everythingof
　　whichwesaythatitcandosomething，isalikecapableofcontraries，
　　e。g。thatofwhichwesaythatitcanbewellisthesameasthat
　　whichcanbeill，andhasbothpotenciesatonce；forthesamepotency
　　isapotencyofhealthandillness，ofrestandmotion，ofbuilding
　　andthrowingdown，ofbeingbuiltandbeingthrowndown。The
　　capacityforcontraries，then，ispresentatthesametime；but
　　contrariescannotbepresentatthesametime，andtheactualities
　　alsocannotbepresentatthesametime，e。g。healthandillness。
　　Therefore，whilethegoodmustbeoneofthem，thecapacityisboth
　　alike，orneither；theactuality，then，isbetter。Alsointhecaseof
　　badthingstheendoractualitymustbeworsethanthepotency；for
　　thatwhich’can’isbothcontrariesalike。Clearly，then，thebaddoes
　　notexistapartfrombadthings；forthebadisinitsnature
　　posteriortothepotency。Andthereforewemayalsosaythatinthe
　　thingswhicharefromthebeginning，i。e。ineternalthings，there
　　isnothingbad，nothingdefective，nothingpervertedforperversion
　　issomethingbad。
　　Itisanactivityalsothatgeometricalconstructionsare
　　discovered；forwefindthembydividing。Ifthefigureshadbeen
　　alreadydivided，theconstructionswouldhavebeenobvious；butas
　　itistheyarepresentonlypotentially。Whyaretheanglesofthe
　　triangleequaltotworightangles？Becausetheanglesaboutonepoint
　　areequaltotworightangles。If，then，thelineparalleltotheside
　　hadbeenalreadydrawnupwards，thereasonwouldhavebeenevident
　　toanyoneassoonashesawthefigure。Whyistheangleina
　　semicircleinallcasesarightangle？Ifthreelinesareequalthe
　　twowhichformthebase，andtheperpendicularfromthecentre-the
　　conclusionisevidentataglancetoonewhoknowstheformer
　　proposition。Obviously，therefore，thepotentiallyexisting
　　constructionsarediscoveredbybeingbroughttoactuality；thereason
　　isthatthegeometer’sthinkingisanactuality；sothatthepotency
　　proceedsfromanactuality；andthereforeitisbymaking
　　constructionsthatpeoplecometoknowthemthoughthesingle
　　actualityislateringenerationthanthecorrespondingpotency。
　　Theterms’being’and’non-being’areemployedfirstlywith
　　referencetothecategories，andsecondlywithreferencetothe
　　potencyoractualityoftheseortheirnon-potencyornonactuality，
　　andthirdlyinthesenseoftrueandfalse。Thisdepends，onthe
　　sideoftheobjects，ontheirbeingcombinedorseparated，sothat
　　hewhothinkstheseparatedtobeseparatedandthecombinedtobe
　　combinedhasthetruth，whilehewhosethoughtisinastate
　　contrarytothatoftheobjectsisinerror。Thisbeingso，whenis
　　whatiscalledtruthorfalsitypresent，andwhenisitnot？Wemust
　　considerwhatwemeanbytheseterms。Itisnotbecausewethinktruly
　　thatyouarepale，thatyouarepale，butbecauseyouarepalewe
　　whosaythishavethetruth。If，then，somethingsarealwayscombined
　　andcannotbeseparated，andothersarealwaysseparatedandcannotbe
　　combined，whileothersarecapableeitherofcombinationorof
　　separation，’being’isbeingcombinedandone，and’notbeing’is
　　beingnotcombinedbutmorethanone。Regardingcontingentfacts，
　　then，thesameopinionorthesamestatementcomestobefalseand
　　true，anditispossibleforittobeatonetimecorrectandat
　　anothererroneous；butregardingthingsthatcannotbeotherwise
　　opinionsarenotatonetimetrueandatanotherfalse，butthesame
　　opinionsarealwaystrueoralwaysfalse。
　　Butwithregardtoincomposites，whatisbeingornotbeing，and
　　truthorfalsity？Athingofthissortisnotcomposite，soasto’be’
　　whenitiscompounded，andnotto’be’ifitisseparated，like
　　’thatthewoodiswhite’or’thatthediagonalisincommensurable’；
　　norwilltruthandfalsitybestillpresentinthesamewayasin
　　thepreviouscases。Infact，astruthisnotthesameinthese
　　cases，soalsobeingisnotthesame；butatruthorfalsityisas
　　follows——contactandassertionaretruthassertionnotbeingthesame
　　asaffirmation，andignoranceisnon-contact。Foritisnot
　　possibletobeinerrorregardingthequestionwhatathingis，save
　　inanaccidentalsense；andthesameholdsgoodregarding
　　non-compositesubstancesforitisnotpossibletobeinerror
　　aboutthem。Andtheyallexistactually，notpotentially；for
　　otherwisetheywouldhavecometobeandceasedtobe；but，asit
　　is，beingitselfdoesnotcometobenorceasetobe；forifit
　　haddonesoitwouldhavehadtocomeoutofsomething。Aboutthe
　　things，then，whichareessencesandactualities，itisnotpossible
　　tobeinerror，butonlytoknowthemornottoknowthem。Butwedo
　　inquirewhattheyare，viz。whethertheyareofsuchandsuchanature
　　ornot。
　　bAsregardsthe’being’thatanswerstotruthandthe
　　’non-being’thatanswerstofalsity，inonecasethereistruthifthe
　　subjectandtheattributearereallycombined，andfalsityiftheyare
　　notcombined；intheothercase，iftheobjectisexistentitexists
　　inaparticularway，andifitdoesnotexistinthiswaydoesnot
　　existatall。Andtruthmeansknowingtheseobjects，andfalsity
　　doesnotexist，norerror，butonlyignorance-andnotanignorance
　　whichislikeblindness；forblindnessisakintoatotalabsenceof
　　thefacultyofthinking。
　　Itisevidentalsothataboutunchangeablethingstherecanbe
　　noerrorinrespectoftime，ifweassumethemtobeunchangeable。
　　E。g。ifwesupposethatthetriangledoesnotchange，weshallnot
　　supposethatatonetimeitsanglesareequaltotworightangles
　　whileatanothertimetheyarenotforthatwouldimplychange。It
　　ispossible，however，tosupposethatonememberofsuchaclasshasa
　　certainattributeandanotherhasnot；e。g。whilewemaysuppose
　　thatnoevennumberisprime，wemaysupposethatsomeareandsome
　　arenot。Butregardinganumericallysinglenumbernoteventhis
　　formoferrorispossible；forwecannotinthiscasesupposethatone
　　instancehasanattributeandanotherhasnot，butwhetherour
　　judgementbetrueorfalse，itisimpliedthatthefactiseternal。