Butevidentlythereisafirstprinciple，andthecausesofthings
　　areneitheraninfiniteseriesnorinfinitelyvariousinkind。For
　　neithercanonethingproceedfromanother，asfrommatter，ad
　　infinitume。g。fleshfromearth，earthfromair，airfromfire，and
　　soonwithoutstopping，norcanthesourcesofmovementforman
　　endlessseriesmanforinstancebeingactedonbyair，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’，buteitheriasthemancomesfromtheboy，bytheboy’s
　　changing，oriiasaircomesfromwater。By’asthemancomesfrom
　　theboy’wemean’asthatwhichhascometobefromthatwhichis
　　comingtobe’or’asthatwhichisfinishedfromthatwhichisbeing
　　achieved’forasbecomingisbetweenbeingandnotbeing，sothat
　　whichisbecomingisalwaysbetweenthatwhichisandthatwhichis
　　not；forthelearnerisamanofscienceinthemaking，andthisis
　　whatismeantwhenwesaythatfromalearneramanofscienceis
　　beingmade；ontheotherhand，comingfromanotherthingaswater
　　comesfromairimpliesthedestructionoftheotherthing。Thisiswhy
　　changesoftheformerkindarenotreversible，andtheboydoesnot
　　comefromthemanforitisnotthatwhichcomestobesomethingthat
　　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
　　eliminatetheGoodwithoutknowingityetnoonewouldtrytodo
　　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
　　thinkifwedonotmakeastopforwhichreasononewhoistracing
　　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
　　thusweshallalsoseewhatnaturalsciencetreatsofandwhether
　　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-1whethertheinvestigationofthe
　　causesbelongstooneortomoresciences，and2whethersucha
　　scienceshouldsurveyonlythefirstprinciplesofsubstance，or
　　alsotheprinciplesonwhichallmenbasetheirproofs，e。g。whether
　　itispossibleatthesametimetoassertanddenyoneandthesame
　　thingornot，andallothersuchquestions；and3ifthescience
　　inquestiondealswithsubstance，whetheronesciencedealswithall
　　substances，ormorethanone，andifmore，whetherallareakin，or
　　someofthemmustbecalledformsofWisdomandtheotherssomething
　　else。And4thisitselfisalsooneofthethingsthatmustbe
　　discussed-whethersensiblesubstancesaloneshouldbesaidtoexistor
　　othersalsobesidesthem，andwhethertheseothersareofonekind
　　orthereareseveralclassesofsubstances，asissupposedbythose
　　whobelievebothinFormsandinmathematicalobjectsintermediate
　　betweentheseandsensiblethings。Intothesequestions，then，aswe
　　say，wemustinquire，andalso5whetherourinvestigationis
　　concernedonlywithsubstancesoralsowiththeessentialattributes
　　ofsubstances。Further，withregardtothesameandotherandlikeand
　　unlikeandcontrariety，andwithregardtopriorandposteriorandall
　　othersuchtermsaboutwhichthedialecticianstrytoinquire，
　　startingtheirinvestigationfromprobablepremisesonly，-whose
　　businessisittoinquireintoallthese？Further，wemustdiscussthe
　　essentialattributesofthesethemselves；andwemustasknotonly
　　whateachoftheseis，butalsowhetheronethingalwayshasone
　　contrary。Again6，aretheprinciplesandelementsofthingsthe
　　genera，orthepartspresentineachthing，intowhichitis
　　divided；and7iftheyarethegenera，aretheythegenerathat
　　arepredicatedproximatelyoftheindividuals，orthehighest
　　genera，e。g。isanimalormanthefirstprincipleandthemore
　　independentoftheindividualinstance？And8wemustinquireand
　　discussespeciallywhetherthereis，besidesthematter，anything
　　thatisacauseinitselfornot，andwhetherthiscanexistapart
　　ornot，andwhetheritisoneormoreinnumber，andwhetherthere
　　issomethingapartfromtheconcretethingbytheconcretethingI
　　meanthematterwithsomethingalreadypredicatedofit，orthere
　　isnothingapart，orthereissomethinginsomecasesthoughnotin
　　others，andwhatsortofcasestheseare。Again9weaskwhetherthe
　　principlesarelimitedinnumberorinkind，boththoseinthe
　　definitionsandthoseinthesubstratum；and10whetherthe
　　principlesofperishableandofimperishablethingsarethesameor
　　different；andwhethertheyareallimperishableorthoseof
　　perishablethingsareperishable。Further11thereisthequestion
　　whichishardestofallandmostperplexing，whetherunityand
　　being，asthePythagoreansandPlatosaid，arenotattributesof
　　somethingelsebutthesubstanceofexistingthings，orthisisnot
　　thecase，butthesubstratumissomethingelse，-asEmpedoclessays，
　　love；assomeoneelsesays，fire；whileanothersayswaterorair。
　　Again12weaskwhethertheprinciplesareuniversalorlike
　　individualthings，and13whethertheyexistpotentiallyor
　　actually，andfurther，whethertheyarepotentialoractualinany
　　othersensethaninreferencetomovement；forthesequestionsalso
　　wouldpresentmuchdifficulty。Further14，arenumbersandlinesand
　　figuresandpointsakindofsubstanceornot，andiftheyare
　　substancesaretheyseparatefromsensiblethingsorpresentin
　　them？Withregardtoallthesemattersnotonlyisithardtoget
　　possessionofthetruth，butitisnoteasyeventothinkoutthe
　　difficultieswell。