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。