Butevidentlythereisafirstprinciple，andthecausesofthings
areneitheraninfiniteseriesnorinfinitelyvariousinkind。For
neithercanonethingproceedfromanother，asfrommatter，ad
infinitum(e。g。fleshfromearth，earthfromair，airfromfire，and
soonwithoutstopping)，norcanthesourcesofmovementforman
endlessseries(manforinstancebeingactedonbyair，airbythe
sun，thesunbyStrife，andsoonwithoutlimit)。Similarlythe
finalcausescannotgoonadinfinitum，-walkingbeingforthesake
ofhealth，thisforthesakeofhappiness，happinessforthesakeof
somethingelse，andsoonethingalwaysforthesakeofanother。And
thecaseoftheessenceissimilar。Forinthecaseof
intermediates，whichhavealasttermandatermpriortothem，the
priormustbethecauseofthelaterterms。Forifwehadtosaywhich
ofthethreeisthecause，weshouldsaythefirst；surelynotthe
last，forthefinaltermisthecauseofnone；noreventhe
intermediate，foritisthecauseonlyofone。(Itmakesnodifference
whetherthereisoneintermediateormore，norwhethertheyare
infiniteorfiniteinnumber。)Butofserieswhichareinfinitein
thisway，andoftheinfiniteingeneral，allthepartsdowntothat
nowpresentarealikeintermediates；sothatifthereisnofirst
thereisnocauseatall。
Norcantherebeaninfiniteprocessdownwards，withabeginning
intheupwarddirection，sothatwatershouldproceedfromfire，earth
fromwater，andsoalwayssomeotherkindshouldbeproduced。For
onethingcomesfromanotherintwoways-notinthesenseinwhich
’from’means’after’(aswesay’fromtheIsthmiangamescomethe
Olympian’)，buteither(i)asthemancomesfromtheboy，bytheboy’s
changing，or(ii)asaircomesfromwater。By’asthemancomesfrom
theboy’wemean’asthatwhichhascometobefromthatwhichis
comingtobe’or’asthatwhichisfinishedfromthatwhichisbeing
achieved’(forasbecomingisbetweenbeingandnotbeing，sothat
whichisbecomingisalwaysbetweenthatwhichisandthatwhichis
not；forthelearnerisamanofscienceinthemaking，andthisis
whatismeantwhenwesaythatfromalearneramanofscienceis
beingmade)；ontheotherhand，comingfromanotherthingaswater
comesfromairimpliesthedestructionoftheotherthing。Thisiswhy
changesoftheformerkindarenotreversible，andtheboydoesnot
comefromtheman(foritisnotthatwhichcomestobesomethingthat
comestobeasaresultofcomingtobe，butthatwhichexistsafter
thecomingtobe；foritisthusthattheday，too，comesfromthe
morning-inthesensethatitcomesafterthemorning；whichisthe
reasonwhythemorningcannotcomefromtheday)；butchangesofthe
otherkindarereversible。Butinbothcasesitisimpossiblethatthe
numberoftermsshouldbeinfinite。Fortermsoftheformerkind，
beingintermediates，musthaveanend，andtermsofthelatterkind
changebackintooneanother，forthedestructionofeitheristhe
generationoftheother。
Atthesametimeitisimpossiblethatthefirstcause，being
eternal，shouldbedestroyed；forsincetheprocessofbecomingisnot
infiniteintheupwarddirection，thatwhichisthefirstthingby
whosedestructionsomethingcametobemustbenon-eternal。
Further，thefinalcauseisanend，andthatsortofendwhich
isnotforthesakeofsomethingelse，butforwhosesakeeverything
elseis；sothatifthereistobealasttermofthissort，the
processwillnotbeinfinite；butifthereisnosuchterm，therewill
benofinalcause，butthosewhomaintaintheinfiniteseries
eliminatetheGoodwithoutknowingit(yetnoonewouldtrytodo
anythingifhewerenotgoingtocometoalimit)；norwouldthere
bereasonintheworld；thereasonableman，atleast，alwaysacts
forapurpose，andthisisalimit；fortheendisalimit。
Buttheessence，also，cannotbereducedtoanotherdefinition
whichisfullerinexpression。Fortheoriginaldefinitionisalways
moreofadefinition，andnotthelaterone；andinaseriesin
whichthefirsttermhasnottherequiredcharacter，thenexthas
notiteither。Further，thosewhospeakthusdestroyscience；forit
isnotpossibletohavethistillonecomestotheunanalysableterms。
Andknowledgebecomesimpossible；forhowcanoneapprehendthings
thatareinfiniteinthisway？Forthisisnotlikethecaseofthe
line，towhosedivisibilitythereisnostop，butwhichwecannot
thinkifwedonotmakeastop(forwhichreasononewhoistracing
theinfinitelydivisiblelinecannotbecountingthepossibilities
ofsection)，butthewholelinealsomustbeapprehendedby
somethinginusthatdoesnotmovefromparttopart-Again，nothing
infinitecanexist；andifitcould，atleastthenotionofinfinity
isnotinfinite。
Butifthekindsofcauseshadbeeninfiniteinnumber，then
alsoknowledgewouldhavebeenimpossible；forwethinkweknow，
onlywhenwehaveascertainedthecauses，thatbutthatwhichis
infinitebyadditioncannotbegonethroughinafinitetime。
Theeffectwhichlecturesproduceonahearerdependsonhis
habits；forwedemandthelanguageweareaccustomedto，andthat
whichisdifferentfromthisseemsnotinkeepingbutsomewhat
unintelligibleandforeignbecauseofitsunwontedness。Foritis
thecustomarythatisintelligible。Theforceofhabitisshownbythe
laws，inwhichthelegendaryandchildishelementsprevailoverour
knowledgeaboutthem，owingtohabit。Thussomepeopledonotlisten
toaspeakerunlesshespeaksmathematically，othersunlesshegives
instances，whileothersexpecthimtociteapoetaswitness。Andsome
wanttohaveeverythingdoneaccurately，whileothersareannoyedby
accuracy，eitherbecausetheycannotfollowtheconnexionofthought
orbecausetheyregarditaspettifoggery。Foraccuracyhas
somethingofthischaracter，sothatasintradesoinargumentsome
peoplethinkitmean。Henceonemustbealreadytrainedtoknowhowto
takeeachsortofargument，sinceitisabsurdtoseekatthesame
timeknowledgeandthewayofattainingknowledge；anditisnot
easytogetevenoneofthetwo。
Theminuteaccuracyofmathematicsisnottobedemandedinall
cases，butonlyinthecaseofthingswhichhavenomatter。Hence
methodisnotthatofnaturalscience；forpresumablythewholeof
naturehasmatter。Hencewemustinquirefirstwhatnatureis:for
thusweshallalsoseewhatnaturalsciencetreatsof(andwhether
itbelongstoonescienceortomoretoinvestigatethecausesandthe
principlesofthings)。
WEmust，withaviewtothesciencewhichweareseeking，first
recountthesubjectsthatshouldbefirstdiscussed。Theseinclude
boththeotheropinionsthatsomehaveheldonthefirstprinciples，
andanypointbesidesthesethathappenstohavebeenoverlooked。
Forthosewhowishtogetclearofdifficultiesitisadvantageous
todiscussthedifficultieswell；forthesubsequentfreeplayof
thoughtimpliesthesolutionofthepreviousdifficulties，anditis
notpossibletountieaknotofwhichonedoesnotknow。Butthe
difficultyofourthinkingpointstoa’knot’intheobject；forinso
farasourthoughtisindifficulties，itisinlikecasewiththose
whoarebound；forineithercaseitisimpossibletogoforward。
Henceoneshouldhavesurveyedallthedifficultiesbeforehand，both
forthepurposeswehavestatedandbecausepeoplewhoinquirewithout
firststatingthedifficultiesarelikethosewhodonotknowwhere
theyhavetogo；besides，amandoesnototherwiseknowevenwhether
hehasatanygiventimefoundwhatheislookingforornot；for
theendisnotcleartosuchaman，whiletohimwhohasfirst
discussedthedifficultiesitisclear。Further，hewhohasheard
allthecontendingarguments，asiftheywerethepartiestoacase，
mustbeinabetterpositionforjudging。
Thefirstproblemconcernsthesubjectwhichwediscussedinour
prefatoryremarks。Itisthis-(1)whethertheinvestigationofthe
causesbelongstooneortomoresciences，and(2)whethersucha
scienceshouldsurveyonlythefirstprinciplesofsubstance，or
alsotheprinciplesonwhichallmenbasetheirproofs，e。g。whether
itispossibleatthesametimetoassertanddenyoneandthesame
thingornot，andallothersuchquestions；and(3)ifthescience
inquestiondealswithsubstance，whetheronesciencedealswithall
substances，ormorethanone，andifmore，whetherallareakin，or
someofthemmustbecalledformsofWisdomandtheotherssomething
else。And(4)thisitselfisalsooneofthethingsthatmustbe
discussed-whethersensiblesubstancesaloneshouldbesaidtoexistor
othersalsobesidesthem，andwhethertheseothersareofonekind
orthereareseveralclassesofsubstances，asissupposedbythose
whobelievebothinFormsandinmathematicalobjectsintermediate
betweentheseandsensiblethings。Intothesequestions，then，aswe
say，wemustinquire，andalso(5)whetherourinvestigationis
concernedonlywithsubstancesoralsowiththeessentialattributes
ofsubstances。Further，withregardtothesameandotherandlikeand
unlikeandcontrariety，andwithregardtopriorandposteriorandall
othersuchtermsaboutwhichthedialecticianstrytoinquire，
startingtheirinvestigationfromprobablepremisesonly，-whose
businessisittoinquireintoallthese？Further，wemustdiscussthe
essentialattributesofthesethemselves；andwemustasknotonly
whateachoftheseis，butalsowhetheronethingalwayshasone
contrary。Again(6)，aretheprinciplesandelementsofthingsthe
genera，orthepartspresentineachthing，intowhichitis
divided；and(7)iftheyarethegenera，aretheythegenerathat
arepredicatedproximatelyoftheindividuals，orthehighest
genera，e。g。isanimalormanthefirstprincipleandthemore
independentoftheindividualinstance？And(8)wemustinquireand
discussespeciallywhetherthereis，besidesthematter，anything
thatisacauseinitselfornot，andwhetherthiscanexistapart
ornot，andwhetheritisoneormoreinnumber，andwhetherthere
issomethingapartfromtheconcretething(bytheconcretethingI
meanthematterwithsomethingalreadypredicatedofit)，orthere
isnothingapart，orthereissomethinginsomecasesthoughnotin
others，andwhatsortofcasestheseare。Again(9)weaskwhetherthe
principlesarelimitedinnumberorinkind，boththoseinthe
definitionsandthoseinthesubstratum；and(10)whetherthe
principlesofperishableandofimperishablethingsarethesameor
different；andwhethertheyareallimperishableorthoseof
perishablethingsareperishable。Further(11)thereisthequestion
whichishardestofallandmostperplexing，whetherunityand
being，asthePythagoreansandPlatosaid，arenotattributesof
somethingelsebutthesubstanceofexistingthings，orthisisnot
thecase，butthesubstratumissomethingelse，-asEmpedoclessays，
love；assomeoneelsesays，fire；whileanothersayswaterorair。
Again(12)weaskwhethertheprinciplesareuniversalorlike
individualthings，and(13)whethertheyexistpotentiallyor
actually，andfurther，whethertheyarepotentialoractualinany
othersensethaninreferencetomovement；forthesequestionsalso
wouldpresentmuchdifficulty。Further(14)，arenumbersandlinesand
figuresandpointsakindofsubstanceornot，andiftheyare
substancesaretheyseparatefromsensiblethingsorpresentin
them？Withregardtoallthesemattersnotonlyisithardtoget
possessionofthetruth，butitisnoteasyeventothinkoutthe
difficultieswell。
