Ingeneral，itisabsurdtomakethefactthatthethingsof
thisearthareobservedtochangeandnevertoremaininthesame
state，thebasisofourjudgementaboutthetruth。Forinpursuingthe
truthonemuststartfromthethingsthatarealwaysinthesamestate
andsuffernochange。Sucharetheheavenlybodies；forthesedonot
appeartobenowofonenatureandagainofanother，butare
manifestlyalwaysthesameandshareinnochange。
Further，ifthereismovement，thereisalsosomethingmoved，
andeverythingismovedoutofsomethingandintosomething；it
followsthatthatthatwhichismovedmustfirstbeinthatoutof
whichitistobemoved，andthennotbeinit，andmoveintothe
otherandcometobeinit，andthatthecontradictorystatements
arenottrueatthesametime，asthesethinkersasserttheyare。
Andifthethingsofthisearthcontinuouslyflowandmovein
respectofquantity-ifoneweretosupposethis，althoughitisnot
true-whyshouldtheynotendureinrespectofquality？Forthe
assertionofcontradictorystatementsaboutthesamethingseemsto
havearisenlargelyfromthebeliefthatthequantityofbodiesdoes
notendure，which，ouropponentshold，justifiestheminsayingthat
thesamethingbothisandisnotfourcubitslong。Butessence
dependsonquality，andthisisofdeterminatenature，thoughquantity
isofindeterminate。
Further，whenthedoctororderspeopletotakesomeparticular
food，whydotheytakeit？Inwhatrespectis’thisisbread’truer
than’thisisnotbread’？Andsoitwouldmakenodifferencewhether
oneateornot。Butasamatteroffacttheytakethefoodwhichis
ordered，assumingthattheyknowthetruthaboutitandthatitis
bread。Yettheyshouldnot，iftherewerenofixedconstantnature
insensiblethings，butallnaturesmovedandflowedforever。
Again，ifwearealwayschangingandneverremainthesame，what
wonderisitiftous，astothesick，thingsneverappearthesame？
Fortothemalso，becausetheyarenotinthesameconditionas
whentheywerewell，sensiblequalitiesdonotappearalike；yet，
forallthat，thesensiblethingsthemselvesneednotshareinany
change，thoughtheyproducedifferent，andnotidentical，sensations
inthesick。Andthesamemustsurelyhappentothehealthyifthe
afore-saidchangetakesplace。Butifwedonotchangebutremainthe
same，therewillbesomethingthatendures。
Asforthosetowhomthedifficultiesmentionedaresuggestedby
reasoning，itisnoteasytosolvethedifficultiestotheir
satisfaction，unlesstheywillpositsomethingandnolongerdemand
areasonforit；foritisonlythusthatallreasoningandall
proofisaccomplished；iftheypositnothing，theydestroy
discussionandallreasoning。Thereforewithsuchmenthereisno
reasoning。Butasforthosewhoareperplexedbythetraditional
difficulties，itiseasytomeetthemandtodissipatethecausesof
theirperplexity。Thisisevidentfromwhathasbeensaid。
Itismanifest，therefore，fromtheseargumentsthatcontradictory
statementscannotbetrulymadeaboutthesamesubjectatonetime，
norcancontrarystatements，becauseeverycontrarietydependson
privation。Thisisevidentifwereducethedefinitionsof
contrariestotheirprinciple。
Similarly，nointermediatebetweencontrariescanbepredicatedof
oneandthesamesubject，ofwhichoneofthecontrariesis
predicated。Ifthesubjectiswhiteweshallbewronginsayingit
isneitherblacknorwhite，forthenitfollowsthatitisandis
notwhite；forthesecondofthetwotermswehaveputtogetheris
trueofit，andthisisthecontradictoryofwhite。
Wecouldnotberight，then，inacceptingtheviewseitherof
HeraclitusorofAnaxagoras。Ifwewere，itwouldfollowthat
contrarieswouldbepredicatedofthesamesubject；forwhen
Anaxagorassaysthatineverythingthereisapartofeverything，he
saysnothingissweetanymorethanitisbitter，andsowithany
otherpairofcontraries，sinceineverythingeverythingispresent
notpotentiallyonly，butactuallyandseparately。Andsimilarlyall
statementscannotbefalsenoralltrue，bothbecauseofmanyother
difficultieswhichmightbeadducedasarisingfromthisposition，and
becauseifallarefalseitwillnotbetruetosayeventhis，and
ifallaretrueitwillnotbefalsetosayallarefalse。
Everyscienceseekscertainprinciplesandcausesforeachof
itsobjects-e。g。medicineandgymnasticsandeachoftheother
sciences，whetherproductiveormathematical。Foreachofthese
marksoffacertainclassofthingsforitselfandbusiesitselfabout
thisasaboutsomethingexistingandreal，-nothoweverquareal；the
sciencethatdoesthisisanotherdistinctfromthese。Ofthesciences
mentionedeachgetssomehowthe’what’insomeclassofthingsand
triestoprovetheothertruths，withmoreorlessprecision。Someget
the’what’throughperception，othersbyhypothesis；sothatitis
clearfromaninductionofthissortthatthereisnodemonstration。
ofthesubstanceor’what’。
Thereisascienceofnature，andevidentlyitmustbedifferent
bothfrompracticalandfromproductivescience。Forinthecaseof
productivesciencetheprincipleofmovementisintheproducerand
notintheproduct，andiseitheranartorsomeotherfaculty。And
similarlyinpracticalsciencethemovementisnotinthething
done，butratherinthedoers。Butthescienceofthenatural
philosopherdealswiththethingsthathaveinthemselvesa
principleofmovement。Itisclearfromthesefacts，then，that
naturalsciencemustbeneitherpracticalnorproductive，but
theoreticalforitmustfallintosomeoneoftheseclasses。And
sinceeachofthesciencesmustsomehowknowthe’what’andusethis
asaprinciple，wemustnotfalltoobservehowthenatural
philosophershoulddefinethingsandhowheshouldstatethe
definitionoftheessence-whetherasakinto’snub’orratherto
’concave’。Forofthesethedefinitionof’snub’includesthematter
ofthething，butthatof’concave’isindependentofthematter；
forsnubnessisfoundinanose，sothatwelookforitsdefinition
withouteliminatingthenose，forwhatissnubisaconcavenose。
Evidentlythenthedefinitionoffleshalsoandoftheeyeandof
theotherpartsmustalwaysbestatedwithouteliminatingthematter。
Sincethereisascienceofbeingquabeingandcapableof
existingapart，wemustconsiderwhetherthisistoberegardedasthe
sameasphysicsorratherasdifferent。Physicsdealswiththe
thingsthathaveaprincipleofmovementinthemselves；mathematicsis
theoretical，andisasciencethatdealswiththingsthatareatrest，
butitssubjectscannotexistapart。Thereforeaboutthatwhichcan
existapartandisunmovablethereisasciencedifferentfrombothof
these，ifthereisasubstanceofthisnatureImeanseparableand
unmovable，asweshalltrytoprovethereis。Andifthereissuch
akindofthingintheworld，heremustsurelybethedivine，andthis
mustbethefirstandmostdominantprinciple。Evidently，then，
therearethreekindsoftheoreticalsciences-physics，mathematics，
theology。Theclassoftheoreticalsciencesisthebest，andof
thesethemselvesthelastnamedisbest；foritdealswiththehighest
ofexistingthings，andeachscienceiscalledbetterorworsein
virtueofitsproperobject。
Onemightraisethequestionwhetherthescienceofbeingqua
beingistoberegardedasuniversalornot。Eachofthe
mathematicalsciencesdealswithsomeonedeterminateclassofthings，
butuniversalmathematicsappliesaliketoall。Nowifnatural
substancesarethefirstofexistingthings，physicsmustbethefirst
ofsciences；butifthereisanotherentityandsubstance，separable
andunmovable，theknowledgeofitmustbedifferentandpriorto
physicsanduniversalbecauseitisprior。
Since’being’ingeneralhasseveralsenses，ofwhichoneis
’beingbyaccident’，wemustconsiderfirstthatwhich’is’inthis
sense。Evidentlynoneofthetraditionalsciencesbusiesitself
abouttheaccidental。Forneitherdoesarchitectureconsiderwhatwill
happentothosewhoaretousethehousee。g。whethertheyhavea
painfullifeinitornot，nordoesweaving，orshoemaking，orthe
confectioner’sart，dothelike；buteachofthesesciences
considersonlywhatispeculiartoit，i。e。itsproperend。Andasfor
theargumentthat’whenhewhoismusicalbecomesletteredhe’llbe
bothatonce，nothavingbeenbothbefore；andthatwhichis，not
alwayshavingbeen，musthavecometobe；thereforehemusthaveat
oncebecomemusicalandlettered’，-thisnoneoftherecognized
sciencesconsiders，butonlysophistic；forthisalonebusiesitself
abouttheaccidental，sothatPlatoisnotfarwrongwhenhesaysthat
thesophistspendshistimeonnon-being。
Thatascienceoftheaccidentalisnotevenpossiblewillbe
evidentifwetrytoseewhattheaccidentalreallyis。Wesaythat
everythingeitherisalwaysandofnecessitynecessitynotinthe
senseofviolence，butthatwhichweappealtoindemonstrations，
orisforthemostpart，orisneitherforthemostpart，noralways
andofnecessity，butmerelyasitchances；e。g。theremightbecold
inthedogdays，butthisoccursneitheralwaysandofnecessity，nor
forthemostpart，thoughitmighthappensometimes。Theaccidental，
then，iswhatoccurs，butnotalwaysnorofnecessity，norforthe
mostpart。Nowwehavesaidwhattheaccidentalis，anditis
obviouswhythereisnoscienceofsuchathing；forallscienceisof
thatwhichisalwaysorforthemostpart，buttheaccidentalisin
neitheroftheseclasses。
Evidentlytherearenotcausesandprinciplesoftheaccidental，
ofthesamekindasthereareoftheessential；foriftherewere，
everythingwouldbeofnecessity。IfAiswhenBis，andBiswhenC
is，andifCexistsnotbychancebutofnecessity，thatalsoofwhich
Cwascausewillexistofnecessity，downtothelastcausatumasit
iscalledbutthiswassupposedtobeaccidental。Thereforeall
thingswillbeofnecessity，andchanceandthepossibilityofa
thing’seitheroccurringornotoccurringareremovedentirelyfrom
therangeofevents。Andifthecausebesupposednottoexistbut
tobecomingtobe，thesameresultswillfollow；everythingwill
occurofnecessity。Forto-morrow’seclipsewilloccurifAoccurs，
andAifBoccurs，andBifCoccurs；andinthiswayifwesubtract
timefromthelimitedtimebetweennowandto-morrowweshallcome
sometimetothealreadyexistingcondition。Thereforesincethis
exists，everythingafterthiswilloccurofnecessity，sothatall
thingsoccurofnecessity。
Astothatwhich’is’inthesenseofbeingtrueorofbeingby
accident，theformerdependsonacombinationinthoughtandisan
affectionofthoughtwhichisthereasonwhyitistheprinciples，
notofthatwhich’is’inthissense，butofthatwhichisoutsideand
canexistapart，thataresought；andthelatterisnotnecessarybut
indeterminateImeantheaccidental；andofsuchathingthe
causesareunorderedandindefinite。
Adaptationtoanendisfoundineventsthathappenbynatureor
astheresultofthought。Itis’luck’whenoneoftheseevents
happensbyaccident。Forasathingmayexist，soitmaybeacause，
eitherbyitsownnatureorbyaccident。Luckisanaccidentalcause
atworkinsucheventsadaptedtoanendasareusuallyeffectedin
accordancewithpurpose。Andsoluckandthoughtareconcernedwith
thesamesphere；forpurposecannotexistwithoutthought。The
causesfromwhichluckyresultsmighthappenareindeterminate；andso
luckisobscuretohumancalculationandisacausebyaccident，but
intheunqualifiedsenseacauseofnothing。Itisgoodorbadluck
whentheresultisgoodorevil；andprosperityormisfortunewhenthe
scaleoftheresultsislarge。
Sincenothingaccidentalispriortotheessential，neitherare
accidentalcausesprior。If，then，luckorspontaneityisacauseof
thematerialuniverse，reasonandnaturearecausesbeforeit。