Fromthesefactswemaysufficientlyperceivethemeaningofthe
ancientswhosaidtheelementsofnatureweremorethanone；butthere
aresomewhospokeoftheuniverseasifitwereoneentity，though
theywerenotallalikeeitherintheexcellenceoftheirstatementor
initsconformitytothefactsofnature。Thediscussionofthemisin
nowayappropriatetoourpresentinvestigationofcauses，for。they
donot，likesomeofthenaturalphilosophers，assumebeingtobe
oneandyetgenerateitoutoftheoneasoutofmatter，butthey
speakinanotherway；thoseothersaddchange，sincetheygeneratethe
universe，butthesethinkerssaytheuniverseisunchangeable。Yet
thismuchisgermanetothepresentinquiry:Parmenidesseemsto
fastenonthatwhichisoneindefinition，Melissusonthatwhichis
oneinmatter，forwhichreasontheformersaysthatitislimited，
thelatterthatitisunlimited；whileXenophanes，thefirstof
thesepartisansoftheOneforParmenidesissaidtohavebeenhis
pupil，gavenoclearstatement，nordoesheseemtohavegrasped
thenatureofeitherofthesecauses，butwithreferencetothe
wholematerialuniversehesaystheOneisGod。Nowthesethinkers，as
wesaid，mustbeneglectedforthepurposesofthepresentinquiry-two
ofthementirely，asbeingalittletoonaive，viz。Xenophanesand
Melissus；butParmenidesseemsinplacestospeakwithmoreinsight。
For，claimingthat，besidestheexistent，nothingnon-existentexists，
hethinksthatofnecessityonethingexists，viz。theexistentand
nothingelseonthiswehavespokenmoreclearlyinourworkon
nature，butbeingforcedtofollowtheobservedfacts，and
supposingtheexistenceofthatwhichisoneindefinition，butmore
thanoneaccordingtooursensations，henowpositstwocausesandtwo
principles，callingthemhotandcold，i。e。fireandearth；andof
theseherangesthehotwiththeexistent，andtheotherwiththe
non-existent。
Fromwhathasbeensaid，then，andfromthewisemenwhohave
nowsatincouncilwithus，wehavegotthusmuch-ontheonehandfrom
theearliestphilosophers，whoregardthefirstprincipleascorporeal
forwaterandfireandsuchthingsarebodies，andofwhomsome
supposethatthereisonecorporealprinciple，othersthatthereare
morethanone，butbothputtheseundertheheadofmatter；andonthe
otherhandfromsomewhopositboththiscauseandbesidesthisthe
sourceofmovement，whichwehavegotfromsomeassingleandfrom
othersastwofold。
DowntotheItalianschool，then，andapartfromit，
philosophershavetreatedthesesubjectsratherobscurely，except
that，aswesaid，theyhaveinfactusedtwokindsofcause，andone
ofthese-thesourceofmovement-sometreatasoneandothersastwo。
ButthePythagoreanshavesaidinthesamewaythattherearetwo
principles，butaddedthismuch，whichispeculiartothem，that
theythoughtthatfinitudeandinfinitywerenotattributesofcertain
otherthings，e。g。offireorearthoranythingelseofthiskind，but
thatinfinityitselfandunityitselfwerethesubstanceofthethings
ofwhichtheyarepredicated。Thisiswhynumberwasthesubstance
ofallthings。Onthissubject，then，theyexpressedthemselves
thus；andregardingthequestionofessencetheybegantomake
statementsanddefinitions，buttreatedthemattertoosimply。For
theybothdefinedsuperficiallyandthoughtthatthefirstsubject
ofwhichagivendefinitionwaspredicablewasthesubstanceofthe
thingdefined，asifonesupposedthat’double’and’2’werethesame，
because2isthefirstthingofwhich’double’ispredicable。But
surelytobedoubleandtobe2arenotthesame；iftheyare，one
thingwillbemany-aconsequencewhichtheyactuallydrew。Fromthe
earlierphilosophers，then，andfromtheirsuccessorswecanlearn
thusmuch。
AfterthesystemswehavenamedcamethephilosophyofPlato，
whichinmostrespectsfollowedthesethinkers，buthad
pecullaritiesthatdistinguisheditfromthephilosophyofthe
Italians。For，havinginhisyouthfirstbecomefamiliarwithCratylus
andwiththeHeracliteandoctrinesthatallsensiblethingsare
everinastateoffluxandthereisnoknowledgeaboutthem，these
viewsheheldeveninlateryears。Socrates，however，wasbusying
himselfaboutethicalmattersandneglectingtheworldofnatureas
awholebutseekingtheuniversalintheseethicalmatters，and
fixedthoughtforthefirsttimeondefinitions；Platoacceptedhis
teaching，butheldthattheproblemappliednottosensiblethingsbut
toentitiesofanotherkind-forthisreason，thatthecommon
definitioncouldnotbeadefinitionofanysensiblething，asthey
werealwayschanging。Thingsofthisothersort，then，hecalled
Ideas，andsensiblethings，hesaid，wereallnamedafterthese，and
invirtueofarelationtothese；forthemanyexistedby
participationintheIdeasthathavethesamenameasthey。Onlythe
name’participation’wasnew；forthePythagoreanssaythatthings
existby’imitation’ofnumbers，andPlatosaystheyexistby
participation，changingthename。Butwhattheparticipationorthe
imitationoftheFormscouldbetheyleftanopenquestion。
Further，besidessensiblethingsandFormshesaystherearethe
objectsofmathematics，whichoccupyanintermediateposition，
differingfromsensiblethingsinbeingeternalandunchangeable，from
Formsinthattherearemanyalike，whiletheFormitselfisineach
caseunique。
SincetheFormswerethecausesofallotherthings，hethought
theirelementsweretheelementsofallthings。Asmatter，thegreat
andthesmallwereprinciples；asessentialreality，theOne；forfrom
thegreatandthesmall，byparticipationintheOne，comethe
Numbers。
ButheagreedwiththePythagoreansinsayingthattheOneis
substanceandnotapredicateofsomethingelse；andinsayingthat
theNumbersarethecausesoftherealityofotherthingsheagreed
withthem；butpositingadyadandconstructingtheinfiniteoutof
greatandsmall，insteadoftreatingtheinfiniteasone，is
peculiartohim；andsoishisviewthattheNumbersexistapart
fromsensiblethings，whiletheysaythatthethingsthemselvesare
Numbers，anddonotplacetheobjectsofmathematicsbetweenFormsand
sensiblethings。HisdivergencefromthePythagoreansinmakingthe
OneandtheNumbersseparatefromthings，andhisintroductionof
theForms，wereduetohisinquiriesintheregionofdefinitionsfor
theearlierthinkershadnotinctureofdialectic，andhismakingthe
otherentitybesidestheOneadyadwasduetothebeliefthatthe
numbers，exceptthosewhichwereprime，couldbeneatlyproducedout
ofthedyadasoutofsomeplasticmaterial。Yetwhathappensisthe
contrary；thetheoryisnotareasonableone。Fortheymakemany
thingsoutofthematter，andtheformgeneratesonlyonce，butwhat
weobserveisthatonetableismadefromonematter，whiletheman
whoappliestheform，thoughheisone，makesmanytables。Andthe
relationofthemaletothefemaleissimilar；forthelatteris
impregnatedbyonecopulation，butthemaleimpregnatesmany
females；yettheseareanaloguesofthosefirstprinciples。
Plato，then，declaredhimselfthusonthepointsinquestion；it
isevidentfromwhathasbeensaidthathehasusedonlytwocauses，
thatoftheessenceandthematerialcausefortheFormsarethe
causesoftheessenceofallotherthings，andtheOneisthecauseof
theessenceoftheForms；anditisevidentwhattheunderlying
matteris，ofwhichtheFormsarepredicatedinthecaseofsensible
things，andtheOneinthecaseofForms，viz。thatthisisadyad，
thegreatandthesmall。Further，hehasassignedthecauseofgood
andthatofeviltotheelements，onetoeachofthetwo，aswesay
someofhispredecessorssoughttodo，e。g。EmpedoclesandAnaxagoras。
Ourreviewofthosewhohavespokenaboutfirstprinciplesand
realityandofthewayinwhichtheyhavespoken，hasbeenconciseand
summary；butyetwehavelearntthismuchfromthem，thatofthosewho
speakabout’principle’and’cause’noonehasmentionedanyprinciple
exceptthosewhichhavebeendistinguishedinourworkonnature，
butallevidentlyhavesomeinklingofthem，thoughonlyvaguely。
Forsomespeakofthefirstprincipleasmatter，whetherthey
supposeoneormorefirstprinciples，andwhethertheysupposethisto
beabodyortobeincorporeal；e。g。Platospokeofthegreatand
thesmall，theItaliansoftheinfinite，Empedoclesoffire，earth，
water，andair，Anaxagorasoftheinfinityofthingscomposedof
similarparts。These，then，haveallhadanotionofthiskindof
cause，andsohaveallwhospeakofairorfireorwater，orsomething
denserthanfireandrarerthanair；forsomehavesaidtheprime
elementisofthiskind。
Thesethinkersgraspedthiscauseonly；butcertainothershave
mentionedthesourceofmovement，e。g。thosewhomakefriendshipand
strife，orreason，orlove，aprinciple。
Theessence，i。e。thesubstantialreality，noonehasexpressed
distinctly。ItishintedatchieflybythosewhobelieveintheForms；
fortheydonotsupposeeitherthattheFormsarethematterof
sensiblethings，andtheOnethematteroftheForms，orthattheyare
thesourceofmovementfortheysaythesearecausesratherof
immobilityandofbeingatrest，buttheyfurnishtheFormsasthe
essenceofeveryotherthing，andtheOneastheessenceoftheForms。
Thatforwhosesakeactionsandchangesandmovementstake
place，theyasserttobeacauseinaway，butnotinthisway，i。e。
notinthewayinwhichitisitsnaturetobeacause。Forthose
whospeakofreasonorfriendshipclassthesecausesasgoods；theydo
notspeak，however，asifanythingthatexistseitherexistedor
cameintobeingforthesakeofthese，butasifmovementsstarted
fromthese。InthesamewaythosewhosaytheOneortheexistentis
thegood，saythatitisthecauseofsubstance，butnotthat
substanceeitherisorcomestobeforthesakeofthis。Therefore
itturnsoutthatinasensetheybothsayanddonotsaythegood
isacause；fortheydonotcallitacausequagoodbutonly
incidentally。
Allthesethinkersthen，astheycannotpitchonanothercause，
seemtotestifythatwehavedeterminedrightlybothhowmanyandof
whatsortthecausesare。Besidesthisitisplainthatwhenthe
causesarebeinglookedfor，eitherallfourmustbesoughtthusor
theymustbesoughtinoneofthesefourways。Letusnextdiscussthe
possibledifficultieswithregardtothewayinwhicheachofthese
thinkershasspoken，andwithregardtohissituationrelativelyto
thefirstprinciples。