第38章

Somethingsareonlyactually，somepotentially，some

potentiallyandactually，whattheyare，viz。inonecaseaparticular

reality，inanother，characterizedbyaparticularquantity，orthe

like。Thereisnomovementapartfromthings；forchangeisalways

accordingtothecategoriesofbeing，andthereisnothingcommonto

theseandinnoonecategory。Buteachofthecategoriesbelongsto

allitssubjectsineitheroftwoways(e。g。’this-ness’-forone

kindofitis’positiveform’，andtheotheris’privation’；andas

regardsqualityonekindis’white’andtheother’black’，andas

regardsquantityonekindis’complete’andtheother’incomplete’，

andasregardsspatialmovementoneis’upwards’andtheother

’downwards’，oronethingis’light’andanother’heavy’)；sothat

thereareasmanykindsofmovementandchangeasofbeing。There

beingadistinctionineachclassofthingsbetweenthepotential

andthecompletelyreal，Icalltheactualityofthepotentialas

such，movement。Thatwhatwesayistrue，isplainfromthe

followingfacts。Whenthe’buildable’，insofarasitiswhatwemean

by’buildable’，existsactually，itisbeingbuilt，andthisisthe

processofbuilding。Similarlywithlearning，healing，walking，

leaping，ageing，ripening。Movementtakeswhenthecompletereality

itselfexists，andneitherearliernorlater。Thecompletereality，

then，ofthatwhichexistspotentially，whenitiscompletelyrealand

actual，notquaitself，butquamovable，ismovement。ByquaImean

this:bronzeispotentiallyastatue；butyetitisnotthecomplete

realityofbronzequabronzethatismovement。Foritisnotthe

samethingtobebronzeandtobeacertainpotency。Ifitwere

absolutelythesameinitsdefinition，thecompleterealityof

bronzewouldhavebeenamovement。Butitisnotthesame。(Thisis

evidentinthecaseofcontraries；fortobecapableofbeingwelland

tobecapableofbeingillarenotthesame-foriftheywere，being

wellandbeingillwouldhavebeenthesame-itisthatwhichunderlies

andishealthyordiseased，whetheritismoistureorblood，thatis

oneandthesame。)Andsinceitisnot。thesame，ascolourandthe

visiblearenotthesame，itisthecompleterealityofthepotential，

andaspotential，thatismovement。Thatitisthis，andthatmovement

takesplacewhenthecompleterealityitselfexists，andneither

earliernorlater，isevident。Foreachthingiscapableofbeing

sometimesactual，sometimesnot，e。g。thebuildablequabuildable；and

theactualityofthebuildablequabuildableisbuilding。Forthe

actualityiseitherthis-theactofbuilding-orthehouse。Butwhen

thehouseexists，itisnolongerbuildable；thebuildableiswhat

isbeingbuilt。Theactuality，then，mustbetheactofbuilding，

andthisisamovement。Andthesameaccountappliestoallother

movements。

Thatwhatwehavesaidisrightisevidentfromwhatallothers

sayaboutmovement，andfromthefactthatitisnoteasytodefineit

otherwise。Forfirstlyonecannotputitinanyclass。Thisisevident

fromwhatpeoplesay。Somecallitothernessandinequalityandthe

unreal；noneofthese，however，isnecessarilymoved，andfurther，

changeisnoteithertotheseorfromtheseanymorethanfromtheir

opposites。Thereasonwhypeopleputmovementintheseclassesisthat

itisthoughttobesomethingindefinite，andtheprinciplesinoneof

thetwo’columnsofcontraries’areindefinitebecausetheyare

privative，fornoneofthemiseithera’this’ora’such’orinany

oftheothercategories。Andthereasonwhymovementisthoughtto

beindefiniteisthatitcannotbeclassedeitherwiththepotency

ofthingsorwiththeiractuality；forneitherthat