’Potency’means(1)asourceofmovementorchange，whichisin
anotherthingthanthethingmovedorinthesamethingquaother；
e。g。theartofbuildingisapotencywhichisnotinthethingbuilt，
whiletheartofhealing，whichisapotency，maybeintheman
healed，butnotinhimquahealed。’Potency’thenmeansthesource，in
general，ofchangeormovementinanotherthingorinthesamething
quaother，andalso(2)thesourceofathing’sbeingmovedbyanother
thingorbyitselfquaother。Forinvirtueofthatprinciple，in
virtueofwhichapatientsuffersanything，wecallit’capable’of
suffering；andthiswedosometimesifitsuffersanythingatall，
sometimesnotinrespectofeverythingitsuffers，butonlyifit
suffersachangeforthebetter——(3)Thecapacityofperformingthis
welloraccordingtointention；forsometimeswesayofthosewho
merelycanwalkorspeakbutnotwellornotastheyintend，thatthey
cannotspeakorwalk。Sotoo(4)inthecaseofpassivity——(5)The
statesinvirtueofwhichthingsareabsolutelyimpassiveor
unchangeable，ornoteasilychangedfortheworse，arecalled
potencies；forthingsarebrokenandcrushedandbentandingeneral
destroyednotbyhavingapotencybutbynothavingoneandbylacking
something，andthingsareimpassivewithrespecttosuchprocesses
iftheyarescarcelyandslightlyaffectedbythem，becauseofa
’potency’andbecausethey’can’dosomethingandareinsomepositive
state。
’Potency’havingthisvarietyofmeanings，sotoothe’potent’
or’capable’inonesensewillmeanthatwhichcanbeginamovement
(orachangeingeneral，foreventhatwhichcanbringthingsto
restisa’potent’thing)inanotherthingorinitselfquaother；and
inonesensethatoverwhichsomethingelsehassuchapotency；andin
onesensethatwhichhasapotencyofchangingintosomething，whether
fortheworseorforthebetter(foreventhatwhichperishesis
thoughttobe’capable’ofperishing，foritwouldnothaveperished
ifithadnotbeencapableofit；but，asamatteroffact，ithasa
certaindispositionandcauseandprinciplewhichfitsittosuffer
this；sometimesitisthoughttobeofthissortbecauseithas
something，sometimesbecauseitisdeprivedofsomething；butif
privationisinasense’having’or’habit’，everythingwillbe
capablebyhavingsomething，sothatthingsarecapablebothbyhaving
apositivehabitandprinciple，andbyhavingtheprivationofthis，
ifitispossibletohaveaprivation；andifprivationisnotina
sense’habit’，’capable’isusedintwodistinctsenses)；anda
thingiscapableinanothersensebecauseneitheranyotherthing，nor
itselfquaother，hasapotencyorprinciplewhichcandestroyit。
Again，allofthesearecapableeithermerelybecausethething
mightchancetohappenornottohappen，orbecauseitmightdoso
well。Thissortofpotencyisfoundeveninlifelessthings，e。g。in
instruments；forwesayonelyrecanspeak，andanothercannotspeak
atall，ifithasnotagoodtone。
Incapacityisprivationofcapacity-i。e。ofsuchaprincipleas
hasbeendescribedeitheringeneralorinthecaseofsomething
thatwouldnaturallyhavethecapacity，orevenatthetimewhenit
wouldnaturallyalreadyhaveit；forthesensesinwhichweshould
callaboyandamanandaeunuch’incapableofbegetting’are
distinct-Again，toeitherkindofcapacitythereisanopposite
incapacity-bothtothatwhichonlycanproducemovementandtothat
whichcanproduceitwell。
Somethings，then，arecalledadunatainvirtueofthiskindof
incapacity，whileothersaresoinanothersense；i。e。bothdunaton
andadunatonareusedasfollows。Theimpossibleisthatofwhich
thecontraryisofnecessitytrue，e。g。thatthediagonalofa
squareiscommensuratewiththesideisimpossible，becausesucha
statementisafalsityofwhichthecontraryisnotonlytruebutalso
necessary；thatitiscommensurate，then，isnotonlyfalsebutalso
ofnecessityfalse。Thecontraryofthis，thepossible，isfound
whenitisnotnecessarythatthecontraryisfalse，e。g。thataman
shouldbeseatedispossible；forthatheisnotseatedisnotof
necessityfalse。Thepossible，then，inonesense，ashasbeensaid，
meansthatwhichisnotofnecessityfalse；inone，thatwhichis
true；inone，thatwhichmaybetrue-A’potency’or’power’in
geometryissocalledbyachangeofmeaning-Thesesensesof
’capable’or’possible’involvenoreferencetopotency。Butthe
senseswhichinvolveareferencetopotencyallrefertotheprimary
kindofpotency；andthisisasourceofchangeinanotherthingorin
thesamethingquaother。Forotherthingsarecalled’capable’，
somebecausesomethingelsehassuchapotencyoverthem，somebecause
ithasnot，somebecauseithasitinaparticularway。Thesameis
trueofthethingsthatareincapable。Thereforetheproperdefinition
oftheprimarykindofpotencywillbe’asourceofchangein
anotherthingorinthesamethingquaother’。
’Quantum’meansthatwhichisdivisibleintotwoormore
constituentpartsofwhicheachisbynaturea’one’anda’this’。A
quantumisapluralityifitisnumerable，amagnitudeifitisa
measurable。’Plurality’meansthatwhichisdivisiblepotentiallyinto
non-continuousparts，’magnitude’thatwhichisdivisibleinto
continuousparts；ofmagnitude，thatwhichiscontinuousinone
dimensionislength；intwobreadth，inthreedepth。Ofthese，limited
pluralityisnumber，limitedlengthisaline，breadthasurface，
depthasolid。
Again，somethingsarecalledquantainvirtueoftheirown
nature，othersincidentally；e。g。thelineisaquantumbyitsown
nature，themusicalisoneincidentally。Ofthethingsthatarequanta
bytheirownnaturesomearesoassubstances，e。g。thelineisa
quantum(for’acertainkindofquantum’ispresentinthe
definitionwhichstateswhatitis)，andothersaremodifications
andstatesofthiskindofsubstance，e。g。muchandlittle，longand
short，broadandnarrow，deepandshallow，heavyandlight，andall
othersuchattributes。Andalsogreatandsmall，andgreaterand
smaller，bothinthemselvesandwhentakenrelativelytoeachother，
arebytheirownnatureattributesofwhatisquantitative；but
thesenamesaretransferredtootherthingsalso。Ofthingsthatare
quantaincidentally，somearesocalledinthesenseinwhichitwas
saidthatthemusicalandthewhitewerequanta，viz。becausethat
towhichmusicalnessandwhitenessbelongisaquantum，andsomeare
quantainthewayinwhichmovementandtimeareso；forthesealso
arecalledquantaofasortandcontinuousbecausethethingsofwhich
theseareattributesaredivisible。Imeannotthatwhichismoved，
butthespacethroughwhichitismoved；forbecausethatisaquantum
movementalsoisaquantum，andbecausethisisaquantumtimeisone。
’Quality’means(1)thedifferentiaoftheessence，e。g。manisan
animalofacertainqualitybecauseheistwo-footed，andthehorseis
sobecauseitisfour-footed；andacircleisafigureofparticular
qualitybecauseitiswithoutangles，-whichshowsthattheessential
differentiaisaquality-This，then，isonemeaningofquality-the
differentiaoftheessence，but(2)thereisanothersenseinwhichit
appliestotheunmovableobjectsofmathematics，thesenseinwhich
thenumbershaveacertainquality，e。g。thecompositenumberswhich
arenotinonedimensiononly，butofwhichtheplaneandthesolid
arecopies(thesearethosewhichhavetwoorthreefactors)；andin
generalthatwhichexistsintheessenceofnumbersbesidesquantity
isquality；fortheessenceofeachiswhatitisonce，e。g。thatof
isnotwhatitistwiceorthrice，butwhatitisonce；for6is
once6。
(3)Allthemodificationsofsubstancesthatmove(e。g。heatand
cold，whitenessandblackness，heavinessandlightness，andtheothers
ofthesort)invirtueofwhich，whentheychange，bodiesaresaid
toalter。(4)Qualityinrespectofvirtueandvice，andingeneral，
ofevilandgood。
Quality，then，seemstohavepracticallytwomeanings，andone
oftheseisthemoreproper。Theprimaryqualityisthedifferentiaof
theessence，andofthisthequalityinnumbersisapart；foritisa
differentiaofessences，buteithernotofthingsthatmoveornot
ofthemquamoving。Secondly，therearethemodificationsofthings
thatmove，quamoving，andthedifferentiaeofmovements。Virtueand
vicefallamongthesemodifications；fortheyindicatedifferentiaeof
themovementoractivity，accordingtowhichthethingsinmotion
actorareactedonwellorbadly；forthatwhichcanbemovedor
actinonewayisgood，andthatwhichcandosoinanother——the
contrary——wayisvicious。Goodandevilindicatequalityespeciallyin
livingthings，andamongtheseespeciallyinthosewhichhavepurpose。
Thingsare’relative’(1)asdoubletohalf，andtrebletoa
third，andingeneralthatwhichcontainssomethingelsemanytimesto
thatwhichiscontainedmanytimesinsomethingelse，andthatwhich
exceedstothatwhichisexceeded；(2)asthatwhichcanheatto
thatwhichcanbeheated，andthatwhichcancuttothatwhichcan
becut，andingeneraltheactivetothepassive；(3)asthe
measurabletothemeasure，andtheknowabletoknowledge，andthe
perceptibletoperception。
(1)Relativetermsofthefirstkindarenumericallyrelated
eitherindefinitelyordefinitely，tonumbersthemselvesorto1。E。g。
thedoubleisinadefinitenumericalrelationto1，andthatwhichis
’manytimesasgreat’isinanumerical，butnotadefinite，
relationto1，i。e。notinthisorinthatnumericalrelationtoit；
therelationofthatwhichishalfasbigagainassomethingelseto
thatsomethingisadefinitenumericalrelationtoanumber；that
whichisn+I/ntimessomethingelseisinanindefiniterelationto
thatsomething，asthatwhichis’manytimesasgreat’isinan
indefiniterelationto1；therelationofthatwhichexceedstothat
whichisexceededisnumericallyquiteindefinite；fornumberis
alwayscommensurate，and’number’isnotpredicatedofthatwhichis
notcommensurate，butthatwhichexceedsis，inrelationtothatwhich
isexceeded，somuchandsomethingmore；andthissomethingis
indefinite；foritcan，indifferently，beeitherequalornotequalto
thatwhichisexceeded-Alltheserelations，then，arenumerically
expressedandaredeterminationsofnumber，andsoinanotherway
aretheequalandthelikeandthesame。Forallrefertounity。Those
thingsarethesamewhosesubstanceisone；thosearelikewhose
qualityisone；thoseareequalwhosequantityisone；and1isthe
beginningandmeasureofnumber，sothatalltheserelationsimply
number，thoughnotinthesameway。
(2)Thingsthatareactiveorpassiveimplyanactiveorapassive
potencyandtheactualizationsofthepotencies；e。g。thatwhichis
capableofheatingisrelatedtothatwhichiscapableofbeing
heated，becauseitcanheatit，and，again，thatwhichheatsis
relatedtothatwhichisheatedandthatwhichcutstothatwhichis
cut，inthesensethattheyactuallydothesethings。Butnumerical
relationsarenotactualizedexceptinthesensewhichhasbeen
elsewherestated；actualizationsinthesenseofmovementtheyhave
not。Ofrelationswhichimplypotencysomefurtherimplyparticular
periodsoftime，e。g。thatwhichhasmadeisrelativetothatwhich
hasbeenmade，andthatwhichwillmaketothatwhichwillbemade。
Foritisinthiswaythatafatheriscalledthefatherofhisson；
fortheonehasactedandtheotherhasbeenactedoninacertain
way。Further，somerelativetermsimplyprivationofpotency，i。e。
’incapable’andtermsofthissort，e。g。’invisible’。
Relativetermswhichimplynumberorpotency，therefore，areall
relativebecausetheirveryessenceincludesinitsnatureareference
tosomethingelse，notbecausesomethingelseinvolvesareference
toit；but(3)thatwhichismeasurableorknowableorthinkableis
calledrelativebecausesomethingelseinvolvesareferencetoit。For
’thatwhichisthinkable’impliesthatthethoughtofitis
