OnthePrinciplesofNature（Deprincipiisnaturae）byThomasAquinasNoticecarefullythatsomethingcanbealthoughitisnot，whereasanotherthingtrulyis。Thatwhichcanbeiscalledbeinginpotency；thatwhichalreadyis，iscalledbeinginact。Buttherearetwokindsofbeing：namelyessentialbeingorthesubstantialbeingofthething（as，forexample，tobeaman）
　　andthisistobeabsolutely。Theotherkindofbeingisaccidentalbeing（as，forexample，tobeawhiteman），andthisistobeafter—a—fashionorinsomequalifiedway。
　　Toeachofthesekindsofbeing（i。e。substantialbeingandaccidentalbeing）thereissomethingwhichisinpotency。Forthereissomethingwhichisinpotencytobeaman，namely，thespermandthemenstrualblood；andthereisalsosomethingwhichisinpotencytobeingwhite，namely，aman。Andthatwhichisinpotencytosubstantialbeingjustasmuchasthatwhichisinpotencytoaccidentalbeingcanbecalledmatter；as，forexample，thespermiswithrespecttothemanandtheman，inrespecttowhiteness。Butthereisadifference。Thematterwhichisinpotencytosubstantialbeingiscalledthematter’outofwhich’whereasthematterwhichisinpotencytoaccidentalbeingiscalledthematter’inwhich’。Again，inastrictwayofspeaking，thatwhichisinpotencytosubstantialbeingiscalledprimematter，however，thatwhichisinpotencytoaccidentalbeingiscalledthesubject：Thisiswhyitissaidthataccidentsareinasubject——andalsowhyitisnotsaidthatsubstantialformisinasubject。Anditisaccordingtothisnotionthat’matter’differsfrom’subject’becausethesubjectdoesnothaveitsbeingfromwhatcomestoitbuthasinitselfcompletebeing（as，forexample，amandoesnotderivehisbeingfromhiswhiteness）。Butmatter，ontheotherhand，doesderiveitsbeingfromwhatcomestoit，since，ofitself，ithasincompletebeing。Therefore，strictlyspeaking，（substantial）formgivesbeingtomatter，whereasaccidentsdonotgivebeingtoasubject，butrather，thesubjecttotheaccidents。
　　Sometimes，however（inpopularterminology），onetermisusedfortheother，thatis，’matter’for’subject’andvice—versa。
　　Again，justaseverythingwhichisinpotencycanbecalled’matter’inthesamewayeverythingbywhichsomethinghasbeing（eithersubstantiallyoraccidentally），canbecalled’form’；forexample，inmansinceheispotentiallywhite，hebecomesactuallywhitethroughwhiteness，andthesperm，sinceitispotentiallymanbecomesactuallymanthroughthesoul。Andbecauseitistheformwhichmakessomethingtobeinact，accordinglytheformiscalled’act’。Moreover，thatwhichbringsaboutsubstantialbeinginactiscalled’substantialform’，andthatwhichbringsaboutaccidentalbeinginactiscalled’accidentalform’。
　　Nowsincegeneration（coming—to—be）isamovementtowardsform，therearetwokindsofgenerationwhichcorrespondtothesetwokindsofforms：absolutecoming—to—becorrespondstosubstantialform—relativecoming—to—be（coming—to—be—in—a—certain—way），correspondstoaccidentalform。Forwheneversubstantialformisintroduced，wesaythatsomethingabsolutelybecomes（i。e。withoutqualification）——forexample，amanbecomesamanoramancomes—to—be。However，whenaccidentalformisintroduced，wedonotsaythatsomethingbecomesabsolutely——butratherthatitbecomesthis——forexample，whenamanbecomeswhitewedonotsaythathebecomesamanorthatamanhascome—to—bebutratherthatthemanbecomeswhiteorcomes—to—bewhite。Andthereisatwo—foldnotionofcorruption（passingaway）whichisopposedtothistwo—foldnotionofgeneration（coming—to—be）——namely，absolutepassing—awayandrelativepassingaway。Absolutegeneration（coming—to—be）andabsolutecorruption（passingaway）existonlywithinthegenusofsubstance。Ontheotherhandrelativegenerationandrelativecorruption（coming—to—be—andpassing—away—insomewayorother）arefoundinalloftheothergenera。Andbecausegenerationisakindofmovementfromnon—beingtobeingand，conversely，corruptionfrombeingtonon—being，itisnotfromjustanykindofnon—beingthatgenerationcomesbutfromnon—beingwhichisbeinginpotency——justas，forexample，thestatuecomesfrombronzewhichisstatueinpotency，notinact。
　　And，therefore，inorderthatgeneration（coming—to—be）comeabout，threethingsarenecessary：
　　namely，apotentialsomethingwhichisthematter，andnot—beinginactwhichistheprivation，andthatthroughwhichitbecomesinact，namely，theform。Letustakeanexample：whenastatue—ismadefrombronze，thebronzewhichisinpotencyfortheformofthestatueis’thematter’；
　　theprivationistheshapelessnessorthelackoftheform（ofstatueinthemoltenbronze）；theshapebywhichwecallitastatueistheform。
　　Theformofstatue，however，isnotthesubstantialform，becausethebronzebeforethecoming—to—beofthisform（ofstatue）hasbeinginact，anditsbeingdoesnotdependuponthisshape（ofstatue）whichisanaccidentalform。Allartificialformsareaccidentalforms。Forartonlyoperatesuponthosethingsalreadyconstitutedinbeingbynature。
　　Thereare，therefore，threeprinciplesofnature，andthesearematter，form，andprivation。Oneoftheseprinciples，namely，theform，isthattowardswhichcoming—to—bemoves：theothertwoareonthesideofthatfromwhichcoming—to—bearises。Hencematterandprivationareinthesamesubjectbutseenfromdifferentviewpoints。Foritisthesamesubjectwhichisbothbronzeandunshaped（withrespecttothestatue）beforetheadventoftheform——butitisforonereasonthatwecallitbronzeandforanotherreasonthatwecallitunshaped。Henceprivationiscalledaprinciple，notessentiallybutaccidentally，becauseitcoincideswiththematter；forexample，wesaythatadoctorbuildssomethingaccidentally，forthedoctorbuildssomethingnotinsofarasheisadoctor，butinsofarasheisabuilderandbuildercoincideswithdoctorinonesubject。Nowaccidentsareoftwokinds。Therearenecessaryaccidentswhicharenotseparatedfromthething，as，forexample，risibilityfromman；andtherearenon—necessaryaccidentswhichareseparated，suchaswhitenessfromman。Soalthoughprivationisanaccidentalprinciple，itdoesnotfollowthatitisnotnecessaryforcoming—to—be。Formatterisneverwithoutprivation：forinsofarasthematterisunderoneformithastheprivationofanotherformandviceversa。Forexample，infirethereistheprivationofairandinairtheprivationoffire。
　　Itshouldbenoticedthatalthoughcoming—to—bearisesfromnot—being，wedonotsaythatnegationisitsprinciple，butrather，privation；andthisisbecausenegationdoesnotdeterminethesubjectforitself。Not—seeingcanbesaidevenofnon—beingsas，forexample，"Chimerasdonotsee。"Likewiseitcanbesaidofbeingswhicharenotintendedbynaturetohavesight，suchasastone。Butprivationissaidonlyofadeterminatesubjectwhichisintendedbynaturetohaveagivenstate：thusblindness，forexample，isonlysaidofthosethingswhichareintendedbynaturetosee。Andbecausecoming—to—bedoesnotarisefromabsolutenon—beingbutfromnon—beingwhichisinacertainsubject，andnotinjustanysubjectbutinadeterminedone，（foritisnotfromjustanynon—burningthingthatfirecomesabout，butfromanon—burningthingwhichbynaturecanbecometheformoffire）——itisbecauseofthisthatprivationisaprinciple。Butinthis，privationasaprinciplediffersfromtheotherprinciplesbecausetheothersareprinciplesbothinbeingandbecoming。Forthatthisshouldbecomeastatueitisnecessarythattherebebronzeand，ultimately，theshapeofthestatue：and，moreover，onceitisastatue，itisagainnecessarythatbothoftheseexist。Butprivationisaprincipleinbecomingandnotinbeing，forwhilethestatueisbecomingitcannotbeastatue。Ifitwereastatue，itcouldnotbebecomingone，becausewhatisbecomingisonlyinsuccessivestages，asaretimeandmotion。Butfromthatwhichalreadyisastatue，thereisnottheprivationofstatueinit。Becauseaffirmationandnegationcannotexistsimultaneously，similarlyneithercanthestateandtheprivationofthatstate。Andsoprivationisanaccidentalprincipleinthesenseexplainedabove；theothertwoareessentialprinciples。
　　Fromwhathasalreadybeensaid，itisevidentthatmatterdiffersfromformandfromprivationaccordingtodefinition。Formatteristhatinwhichbothformandprivationareunderstood，justasbothashapeandalackofashapeareunderstoodinthebronze。Andsometimesthewayinwhichwenamethematterinvolvesthenotionofprivationandsometimesitdoesnotinvolvethenotionofprivation；forexample，bronze，althoughitisthematterofthestatuedoesnotinvolvethenotionofprivationbecausewhenIsay"bronze"，thelackofaformorthelackofashapeisnotincludedinmyconcept。Ontheotherhand，flour，sinceitisthematterwithrespecttobreaddoesinvolveinitselftheprivationoftheformofbread，becausewhenIsay"flour"thelackofformorthedisorganizationopposedtotheformofbreadissignified。Andbecauseincoming—to—bethematterorthesubjectremains，buttheprivationdoesnot，andneitherdoesthecompositeofmatterandprivation，accordingly，matterwhichdoesnotinvolvethenotionofprivationremains；however，thatmatterwhichdoesinvolvethenotionofprivation，istransitory。
　　Itshouldalsobenotedthatsomematterhasacompositionofform；forexample，althoughthebronzeisthematterwithrespecttothestatue，nevertheless，thebronzeitselfisacompositeofmatterandform。Therefore，bronzecannotbecalledprimematterbecauseithasamatter。Onlythatmatterwhichcanbeunderstoodwithoutanyformandprivation，butwhichisthesubjectofbothformandprivation，iscalledprimematterbecausethereisnotanyothermatterpriortoit。Andthisprimematterisalsocalled"hyle"。
　　Becauseallknowledgeandeverydefinitionisthroughtheform，therefore，primemattercannotbeknownordefinedbyitself，butbythecomposite：andsowesaythatprimematteristhatwhichisrelatedtoallformsandallprivationslikethebronzeisrelatedtothestatueandtotheprivationofsomefigure。
　　Andprimematterheremeansprimeinanabsoluteway。Forsomethingcanalsobecalledprimarywithrespecttoacertaingenus，suchaswaterbeingtheprimematterinthegenusofliquids。Nevertheless，waterisnotprimeinanabsoluteway，becauseitisacompositeofmatterandform；henceithasamatterpriortoit。
　　Againitshouldbenotedthatbothprimematterandformneithercome—to—benorpass—awaybecauseallcoming—to—beisfromsomethingtosomething。Nowthatfromwhichthecoming—to—beisfromisthematter；andthattowhichthecoming—to—beistoistheform。Therefore，ifthematterortheformalsocome—to—be，therewouldbeamatterofthematterandaformoftheformadinfinitum。Hence，strictlyspeaking，onlythecompositecomes—to—be。
　　Againitshouldbenotedthatprimematterissaidtobenumericallyoneinallthings。
　　But"numericallyone"canbesaidintwoways：firstofall，ofthatwhichhasaonedeterminedforminnumberas，forexample，Socrates。Nowprimematterisnotsaidtobenumericallyoneinthiswaysince，initself，itdoesnothaveanyoneform。Secondly，somethingcanalsobesaidtobenumericallyonewhichiswithoutthedispositionswhichwouldmakeitdifferaccordingtonumber。Anditisinthiswaythatprimematterissaidtobenumericallyone，becauseitsconceptinvolvesthelackofallofthedispositionswhichaccountfordifferentiationinnumber。
　　Andfinallyitshouldbenotedthatalthoughtheconceptofprimematterdoesnotincludeanyformorprivation，justasintheconceptofbronzethereisincludedneitherashapenorthelackofashape，neverthelessprimematterisneverwithoutsomeformandprivation。Forsometimesitisunderoneformandsometimesunderanotherform。Butprimemattercannotexistbyitselfalone，becausebyitsverydefinitionitdoesnothaveanyform，andsodoesnothaveanyactualexistence，sincebeinginactisonlythroughtheform。
　　Butprimematterisonlyinpotency。And，therefore，anythingwhatsoeverthatexistsinactcannotbecalledprimematter。
　　Fromwhathasbeensaiditisevidentthattherearethreeprinciplesofnature，namely，matter，form，andprivation。Butthesethreearenotsufficienttoexplaincoming—to—be。Forwhateverisinpotencycannotreduceitselftoact：forexample，thebronzewhichisastatueinpotencydoesnotmakeitselfastatue，butrequiresanagentwhichdrawsoutfrompotencytoacttheformofthestatue。Neithercantheformdrawitselfintoactfrompotency。
　　AndhereIamspeakingoftheformgeneratedwhichwecallthetermofgeneration。Fortheformdoesnotexistunlessitexistsinfact：theagent，however，existsinbecoming，thatis，whilethethingiscoming—to—be。
　　Besidesthematterandtheform，therefore，theremustexistsomeotherprinciplewhichacts，andthisiscalledtheefficientcauseor，themovingcause，ortheagent，ortheprinciplefromwhencethemovementexists。
　　Andbecause，asAristotlepointsoutinBk。IIoftheMetaphysics，everythingwhichacts，actsonlywhenintendingsomething，afourthprinciplemustalsobeposited——namely，thatwhichisintendedbytheagent，andthisiscalledtheend。Anditshouldbenotedthatalthougheveryagentwhethernaturalorvoluntaryintendsanend，neverthelessitdoesnotfollowthateveryagentknowstheendordeliberatesabouttheend。Fortoknowtheendisnecessaryonlyinthosethingswhoseactionsarenotdeterminedbutwhichcanmovetowardsopposites，asisthecasewithvoluntaryagents；
　　forthese（voluntaryagents）itisnecessarythattheyknowtheendthroughwhichtheydeterminetheiractions。Innaturalagents，however，theiractionsaredetermined，henceitisnotnecessarytochoosethosethings（means）
　　whicharefortheend。WemayusetheexamplegivenbyAvicennaofthecithara（amusicalinstrumentresemblingalyre）playerwhodoesnothavetodeliberateabouteachnoteofachordsincethenotesaredeterminedwithinit，forshouldsomeonedeliberate，therewouldbeadelaybetweenthenoteswhichwouldbediscordant。Allofthiscanbeseenmoreclearlywithrespecttovoluntaryagentswhodeliberatethanwithnaturalagents——and，accordingly，itisevidentafortiorithatifthevoluntaryagentwhosedeliberationismoreevident，doesnotalwaysdeliberate，thencertainlyneitherdoesthenaturalagent。Itisthereforepossibleforanaturalagenttointendanendwithoutdeliberationandthisintendingisnothingotherthanhavinganaturalinclinationtowardssomething。
　　Fromwhathasbeensaiditisevidentthattherearefourcauses，namely，thematerial，theefficient，theformal，andthefinal。Nowalthoughprincipleandcausearespokenofinaquasi—convertibleway，asissaidinBk。VoftheMetaphysics，nevertheless，inthePhysics，Aristotlesetsdownfourcausesandthreeprinciples。Furthermore，heacceptsascausesjustasmuchextrinsicasintrinsicones。Matterandformarecalledintrinsiccausesofthethingduetothefactthattheyaretheconstitutivepartsofthething。Theefficientandthefinalcausesarecalledextrinsiccausesbecausetheyareoutsideofthething。Butheacceptsonlytheintrinsiccausesasprinciples。
　　Moreover，privationisnotnamedamongthecausesbecauseitisanaccidentalprinciple，aswassaidearlier。Andwhenwespeakofthefourcauses，wemeantheessentialcausestowhich，however，accidentalcausesarereducedbecauseeverythingwhichisaccidentalisreducedtothatwhichisessential。
　　ButalthoughAristotleconsidersprinciplesasintrinsiccausesinBk。IofthePhysics，nevertheless，ashesaysinBk。XIoftheMetaphysics（thisistodayBk。XII，1170b22—30），"principle"isproperlysaidofextrinsiccausesand"elements"ofthosecauseswhicharethepartsofthething，thatis，oftheinstrinsiccauses。However"cause"isusedwithrespecttoboth，althoughsometimesonetermisusedfortheother；foreverycausecanbecalledaprincipleandeveryprinciple，acause。But，thenotionofcauseseemstoaddsomethingoverandabovewhatiscommonlycalledprinciple，becausethatwhichisfirst，whetherornotsomethingposteriorfollowsfromit，canbecalledaprinciple，justastheartisaniscalledtheprincipleoftheknifebecauseaknifecomesintobeingasaresultofhisactivity：
　　butwhensomethingismovedfromblacknesstowhiteness，blacknessiscalledtheprincipleofthatmovement（anduniversally，everythingfromwhichamovementbeginsiscalledaprinciple），nevertheless，blacknessisnotthatfromwhichthebeingofwhitenessfollows。But"cause"issaidonlyofthatthingwhichisfirstfromwhichaposteriorthingfollowsinbeing（thatis，withrealdependence）。Hence，acauseisthatfromthebeingofwhichanotherbeingfollows。Accordingly，thatwhichisfirstfromwhichthemovementbeginscannotbecalledacauseessentially（perse）evenifitiscalledaprinciple。Thisisthereasonprivationisplacedamongtheprinciplesbutnotamongthecauses，becauseprivationisthatfromwhichthecoming—to—bebegins。Butprivationcanalsobecalledacauseperaccidens，insofarasitcoincideswiththematter，aswasexplainedearlier。
　　Moreover，theterm"element"isusedproperlyonlyofthecausesfromwhichthecompositionofthethingresults——which，properlyspeaking，arematerialcauses。Andagain，notfromjustanymaterialcausewhatsoeverbutfromthatfromwhichresultstheprimarycompositionofthething；forexample，wedonotsaythatthelimbsaretheelementsofthemanbecausethelimbsarethemselvescomposedofotherthings。Butwedocallearthandwaterelementsbecausethesearenotcomposedofotherbodies——butfromtheseelementsresultstheprimarycompositionofnaturalbodies。ThusAristotleinBk。VoftheMetaphysicssaysthat"anelementisthatfromwhichathingisprimarilycomposed，andisinthething，andisnotdividedaccordingtotheform"。Theexplanationofthefirstpartofthisdefinitionnamely，"thatfromwhichathingisprimarilycomposed"，isalreadyclearfromwhathasbeensaidabove。Thesecondpart，namely，"andisinthething"，isplacedinthedefinitioninordertodifferentiate（theelementfrom）
　　thatothermatter（primematter）whichtotallypasses—awaythroughcoming—to—be：
　　forexample，thebreadisthematterofblood，butbloodonlycomes—to—beifthebreadpasses—away；hencethebreaddoesnotremaininthebloodandsothebreadcannotbecalledanelementofblood。Butforittobeanelementitmustremaininsomeway，sinceitdoesnotentirelypass—away，asissaidinthetreatiseOnGeneration。Thethirdpartofthedefinition，namely，"andisnotdividedaccordingtotheform"isplacedinthedefinitiontodifferentiatetheelementfromthosethingswhichhavediversepartsinform，thatis，inspecies；forexample，thehand，whosepartsarefleshandbone，butwhichdifferaccordingtospecies；
　　forexample，anypartwhatsoeverofwateriswater。Itisnotnecessarytothebeingoftheelementtobenotdividedaccordingtoquantity，itissufficientifitbenotdividedaccordingtospecies。Ifsomethingisalsonotdividedinanyway，itiscalledanelement，aslettersaresaidtobetheelementsofwords。Accordingly，itisevidentfromwhathasbeensaidthat"principle"insomewayinwhichitisusedimpliesmorethan"cause"，and"cause"，morethan"element"——andthisiswhattheCommentator（Averroes）saysinhiscommentaryonBk。VoftheMetaphysics。
　　Havingseenthattherearefourgeneraofcauses，itshouldbenotedthatitisnotimpossibleforasamethingtohaveseveralcauses，suchasthestatuewhosecauseisbronzeandtheartisan，buttheartisanastheefficientcause，bronzeasthematerialcause。Norisitimpossiblethatasamethingbethecauseofcontraries，justasthehelmsmanisthecauseofthesafetyoftheshipandofitssinking；butofthelatterbyhisabsence，andoftheformerbyhispresence。
　　Itshouldalsobenotedthatitispossiblethatasamethingbecauseandcausedwithrespecttothesamethingbutindifferentways：forexample，walkingisthecauseofhealthinthewayofefficientcausality，buthealthisthecauseofwalkinginthewayoffinalcausality，forsometimeswalkingisdoneforthesakeofhealth。Anotherexampleisthatthebodyisthematterofthesoul，whilethesoulistheformofthebody。Theefficientcauseiscalledacausewithrespecttotheend，fortheendcanonlyexistinactthroughtheoperationoftheagent：buttheendiscalledthecauseoftheefficientcause，fortheefficientcauseoperatesonlythroughtheintentionoftheend。Hencetheefficientcauseiscauseofthatwhichistheend，as，forexample，walkingforthesakeofhealth；neverthelesstheefficientcausedoesnotmaketheend，thatis，itdoesnotmaketheendtobeafinalcause。Adoctor，forexample，makeshealthtobeinact，nevertheless，hedoesnotmakehealthbeanend。Theend，however，isnotthecauseofthatwhichistheefficientcause，butitisthecausethatanefficientcausebeanefficientcause。Forhealthdoesnotmakethedoctortobeadoctor（andIamspeakingofthehealthresultingfromtheoperationofthedoctor）butitdoesmakethedoctorbeanefficientcause。
　　Similarlytheendmakesthematterbethematerialcauseandtheformbetheformalcause，sincethematterreceivestheformonlyforanend，andtheformperfectsthematteronlyforandend。Hencetheendiscalledthecauseofcausesbecauseitisthecauseofthecausalityinallcauses。
　　Alsomatteriscalledthecauseoftheforminsofarastheformexistsonlyinmatter；andsimilarlytheformisthecauseofthematter，insofarasmatterhasbeinginactonlythroughtheform。FormatterandformaresaidtobemutuallyrelatedasissaidinBk。IIofthePhysics。Fortheyaresaidinrelationtothecomposite，asarepartsinrelationtothewhole，andthesimpleinrelationtothecomposite。
　　Butbecauseeverycause，insofarasitisacause，isnaturallypriortowhatiscaused，itshouldbenotedthat"prior"issaidintwoways，asAristotlesaysinBk。XVIofOnAnimals（c。f。OntheGenerationofAnimalsII，6，742a21）。Throughthisdiversity，somethingcanbecalledbothpriorandposteriorandcauseandcausedwithrespecttothesamething。
　　Forsomethingiscalledpriortoanotheringenerationandtimeorpriorinsubstanceandcompleteness。Therefore，sincetheoperationofnatureisfromtheimperfecttotheperfectandfromtheincompletetothecomplete，theimperfectispriortotheperfectaccordingtogenerationandtime，buttheperfectispriortotheimperfectaccordingtosubstance：forexample，itcanbesaidthatthemanispriortotheboyinsubstanceandcompleteness，buttheboyispriortothemaningenerationandtime。But，althoughinthingscapableofcoming—to—be，theimperfectispriortotheperfectandpotencyispriortoact——consideringthatinanysubjectthatwhatispriorisimperfectratherthanperfectandinpotencyratherthaninact——nevertheless，absolutelyspeaking，itisnecessarythatwhatisinactandperfectbeprior；becausewhatreducespotencytoactisinactandwhatperfectstheimperfectisperfect。Thematterispriortotheformingenerationandtime，forthattowhichsomethingcomesispriortothatwhichcomestoit。Buttheformispriortothematterinsubstanceandcompletebeingbecausethematterhascompletebeingonlythroughtheform。Similarlytheefficientcauseispriortotheendingenerationandtime，sincethemovementtowardstheendisbroughtaboutbytheefficientcause；buttheendispriortotheefficientcause，insofarasitisefficientcause，insubstanceandcompleteness，sincetheactionoftheefficientcausebringsaboutcompletenessonlythroughtheend。Accordingly，thesetwocauses，thematerialandtheefficientarepriorbywayofgeneration；
　　buttheformandtheendarepriorbywayofperfection。
　　Anditshouldbenotedthattherearetwokindsofnecessity，namely，absolutenecessityandconditionalnecessity。Thatnecessityisabsolutewhichproceedsfrompriorcausesintheorderofgeneration，andthesearethematerialandtheefficientcauses；forexamplethenecessityofdeathwhichcomesaboutfrommatter，namelyfromthedispositionofcontrarycomponents——anditiscalledabsolutebecausethereisnoimpedimenttoit。Thisnecessityisalsocalledthenecessityofmatter。Ontheotherhand，conditionalnecessityproceedsfromcauseswhichareposterioringeneration，namely，fromtheformandtheend；forexample，wesaythatitisnecessarythattherebeconceptionifamanistobegenerated。Andthisnecessityisalsocalledconditional，becauseitisnotabsolutelynecessarythatthiswomanconceivebutonlyunderthiscondition，namely，ifamanistobegenerated。Andthisnecessityiscalledthenecessityoftheend。
　　Anditshouldbenotedthatthreeofthecauses，namely，theform，theendandtheefficientcause，cancoincideinonethingasisevidentinthecoming—to—beoffire。
　　Forfirebringsfiretobe，thereforefireistheefficientcauseinsofarasitbringstobe；andagain，fireistheforminsofarasitmakestobeinactwhatbeforewasinpotency；andagainitistheendinsofarasitistheintentionoftheagentandinsofarastheoperationoftheagentisterminatedinit。Buttherearetwokindsofends，namely，theendofthegenerationandtheendofthethinggenerated，suchasisevidentinthegenerationofaknife：fortheformofaknifeistheendofthegeneration，butcutting，whichistheoperationoftheknife，istheendofthethinggenerated，thatis，theknife。However，sometimestheendofthegenerationcoincideswiththeothertwoabove—mentionedcauses（theformandtheefficientcause），namely，whenthegenerationisofwhatissimilarinspecies；forexample，whenamangeneratesamanoranolivetreegeneratesanolivetreewhich（coincidenceofform，efficientcause，andend）cannotbeunderstoodoftheendofthethinggenerated。
　　Neverthelessitshouldbenotedthattheendisidenticalwiththeformnumerically，becauseitisthesamesomethingnumericallywhichistheformgeneratedandistheendofgeneration。Buttheendofthegenerationisnotidenticalwiththeefficientcauseinthesamenumberbutinthesamespecies。Foritisimpossiblethatthemakerandthethingmadebenumericallythesame，buttheycanbespecificallythesame；forexample，whenamangeneratesaman，themangeneratingandthemangeneratedaredifferentbynumberbutofthesamespecies。However，themattercannotcoincidewiththeothercausesbecausethematterbythefactthatitisabeinginpotency，hasthenotionofimperfection；buttheothercauses，sincetheyareinact，involvethenotionofperfection；moreover，theperfectandtheimperfectdonotcoincideinthesamething。
　　Accordingly，havingseenthattherearefourcauses，namely，theefficient，thematerial，theformal，andthefinalitshouldbeknownthatthesesamecausesaredividedinmanyways。Therecanbepriorcauseandposteriorcause，aswhenwesaythatboththeartandthedoctorarethecauseofhealth，buttheartisthepriorcauseandthedoctortheposteriorcause。Andthesamedivisionholdsfortheformalcauseandtheothercauses。Andnoticecarefullythatweshouldalwaysleadbackaquestiontothefirstcause。
　　Forexample，ifweask"whyisthismanhealthy？"theansweris"Becausethedoctorhealedhim"Andsoweshouldaskagain，"Bywhatmeansdidthedoctorhealhim？"——"Throughtheactofhealingwhichhepossesses。"
　　Itshouldalsobenotedthatposteriorcauseisalsocalledproximatecauseandpriorcause，remotecause。Hencethesetwodivisionsofcauses——priorandposterior，remoteandproximate——signifythesamething。However，itshouldbeobservedthatalwayswhatismoreuniversaliscalledremotecause，whatismoreparticulariscalledproximatecause。Forexample，wesaythattheproximateformofmanishisdefinition，namely，rationalmortalanimal；butanimalismoreremoteandsubstanceagainmoreremote。Andsimilarlytheproximatematterofthestatueisbronze，buttheremotematterismetalandtheagainmoreremoteisbody。
　　Again，（accordingtoanotherdivision）ofcauses，someareessentialandsomeareaccidental。
　　Acauseiscalledessentialwhichisthecauseofsomethinginsofarasitisthiskindofthing——forexample，thebuilderisthecauseofthehouseandthewoodisthematterofthebench。Acauseiscalledaccidentalwhichhappens（tocoincidewith）anessentialcause—forexample，whenwesaythatthegrammarian；builds（ahouse）。Forthegrammarianiscalledacauseofthebuildingaccidentally，forhedoessonotinsofarasheisgrammarian，butinsofarasheisbuilderandithappensthathebeagrammarian。Andthecaseissimilarintheothercauses。
　　Again，（accordingtoanotherdivision）ofcauses，certainonesaresimple，othersarecomposite。
　　Acauseiscalledsimplewhenwhatistheessentialcauseisalonecalledcauseoralsowhenwhatistheaccidentalcauseisalonecalledcause——forexampleifwesaythatthebuilderisthecauseofthehouseand，similarly，ifwesaythedoctoristhecauseofthehouse。Howeveracauseiscalledcompositewhenbotharesaidtobecauses——forexample，ifwesaythedoctor—builderisthecauseofthehouse。AcausecanalsobecalledsimpleinthewayinwhichAvicennaexplainsit：thatwhichcauseswithoutbeingunitedtoanother，asthebronzeofstatue——forthestatueisofbronzewithouttheadditionofanyothermatter——andjustasitissaidthatthedoctorproduceshealthorthatfireproducesheat。Howeverhecallsacausecompositewhenmanythingsmustcometogetherinthatwhichisacause，justasonemanisnotthecauseofthemovementoftheshipbutmanyandasonestoneisnotthematterofthehouse，butmany。
　　Again，（accordingtoanotherdivision）ofcauses，someareactualandothersarepotential。
　　Anactualcauseisonewhichactuallycausesathing，asthebuilderwhenheisbuilding，orthebronzewhenastatueismadeofit。Apotentialcauseisonewhich，althoughitisnotcausingthethinginact，neverthelesscancauseit，asthebuilderwhileheisnotbuilding。Anditshouldbenotedthatinspeakingofactualcausesitisnecessarythatthecauseandthecausedexistsimultaneously，suchthatifoneis，theothermustalsobe。Forifabuilderbeinact，itisnecessarythathebuild。Andifthereisbuildinginact，theremustbeabuilderinact。Butthisisnotnecessaryincauseswhichareonlypotential。Anditshouldbenotedmoreoverthatauniversalcauseisrelatedtoauniversaleffect，whileasingularcauseisrelatedtoasingulareffect，justaswesaythatbuilderisthecauseofhouseandthisbuilderisthecauseofthishouse。
　　Itshouldalsobenotedthatinspeakingoftheintrinsicprinciple，namely，matterandform，thereisanagreementanddifferenceofprinciplesaccordingtotheagreementanddifferenceofwhatresultsfromtheprinciples。Forcertainthingsarenumericallythesame，suchasSocratesandthisman（inpointingatSocrates）。Otherthingsarenumericallydiversebutthesameinspecies，suchasSocratesandPlato，whoalthoughtheyagreeasmen（humanspecies）
　　nevertheless，differbynumber。Alsocertainthingsdifferaccordingtospeciesbutwearethesameaccordingtogenus；forexample，manandassarebothinthegenusanimal。Againcertainthingsarediverseingenusbutarethesameonlyaccordingtoanalogy；suchassubstanceandquantity，whichdonotagreeinanygenusbutwhicharebroughttogetheronlyaccordingtoanalogy。Fortheyarefoundtogetheronlyinthatwhichisbeing；being，howeverisnotagenus，sinceitisnotpredicatedunivocally，butanalogously。
　　Inordertounderstandthis，however，itshouldbeknownthatsomethingispredicatedofmanyinthreeways：univocally，equivocallyandanalogously。Aunivocalpredicationoccurswhenonethingispredicatedaccordingtothesamenameandaccordingtothesamenature，thatis，thesamedefinition，as"animal"
　　ispredicatedof"man"and"ass"。Forbothofthesearecalled"animal"
　　andeachofthemisalivingsubstancecapableofsensation，whichisthedefinitionofanimal。Equivocalpredicationoccurswhensomethingispredicatedofothersaccordingtothesamenameandaccordingtodifferentnatures，as"dog"issaidofa"barkinganimal"anda"stellerconstellation"，whichthingsagreeonlyinnameandnotindefinitionorsignification；forthatwhichissignifiedbythenameisthedefinition，asissaidinBk。IV
　　oftheMetaphysics。Ananalogicalpredicationoccurswhenonethingispredicatedofmany，whichareofdifferentnatures，butofwhichonesomethingisattributedtothem，as"healthy"issaidofthe"animalbody"，andof"urine"，andofthe"medicine"but"healthy"doesnotsignifyexactlythesamethinginallofthem。For"healthy"issaidof"urine"asofasignofgoodhealth，of"thebody"，asofitssubject，of"themedicine"
　　asofacause。Nevertheless，allofthesenaturesareattributedtoaoneend，namely，health。Forsometimesthosethingswhicharebroughttogetheraccordingtoanalogy，thatisinproportion，orcomparison，oragreement，areattributedtooneend，asisevidentintheaboveexample；sometimesinoneagent，as"doctor"issaidbothofonewhooperatesthroughartandofonewhooperateswithoutart，suchasthemidwife——andthesamealsoholdsforinstruments，butthroughattributiontoaoneagentwhichistheartofmedicine。Alsosometimestheanalogyisbasedthroughattributiontoaonesubjectaswhen"being"issaidofsubstanceandofquantityandofquality，andoftheotherpredicaments。Foritisnotforexactlythesamereasonthatsubstanceissaidofbeing，andquantity，andtheothers——butallofthemarecalledbeingbythefactthattheyareattributedtosubstance，whichisthesubjectoftheothers。And，therefore，beingissaidprimarilyofsubstanceandsecondarilyoftheothers。Accordingly，beingisnotthegenusofsubstanceandquantitybecausenogenusispredicatedprimarilyandsecondarilyofitsspecies。Beingispredicatedanalogously。Anditisinthislightthatwesaythatsubstanceandquantitydifferingenus，butarethesameaccordingtoanalogy。
　　Wherefore，ofthosethingswhicharenumericallyone，boththeformandthematterarenumericallyone，asinthecaseofTulliusandofCicero。Moreover，ofthosethingswhicharethesamespecifically，butdifferbynumber，boththematterandtheformarenotthesamenumericallybutspecificallyasinthecaseofSocratesandofPlato。Andsimilarly，ofthosethingswhicharethesamegenerically，theirprinciplesaregenericallythesame，asinthecaseofthesoulandthebodyofanassandofahorsewhichdifferspecificallybutarethesamegenerically。Anditisalsosimilarforthosethingswhichagreeonlyaccordingtoanalogy，fortheirprinciplesaresimilaronlyaccordingtoanalogyorproportion。Formatter，form，andprivation，orpotencyandactareprinciplesofsubstanceandoftheothergenera。Nevertheless，thematterofsubstanceandofquantity（andsimilaritywithrespecttoformandprivation）differgenerically，butagreeonlyaccordingtoaproportionwhichconsistsinthis——justasthematterofsubstanceisrelatedtosubstanceinthenatureofmatter，soisthematterofquantityrelatedtoquantity。However，justassubstanceisthecauseofalltheothergenera，sotheprinciplesofsubstancearetheprinciplesofalltheothergenera。