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。