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Aristotleisawarethathisargumentsandconclusionsmayprovokethe
chargeofputtingrestrictionsonmathematics.Heanticipatesthechargeand
writesthat“ourreasoningwhichrejectstherealizationofinfinitydoesnot
deprivemathematiciansoftheirtheories;afterall,theyhavenoneedofsuch
aninfinityandtheydonotuseit;allmathematiciansneedisthatthesegment
theyconsider,whilebounded,beaslargeasnecessary,”7and,ofcourse,as
smallasnecessary,whichheaddsinmanyotherplaces.
Theancientsdistinguishedtwokindsofinfinity,potentialandactual.
Apotentialinfinityisthepossibilityofconsideringarbitrarilylargefinitesets.
Anactualinfinityisgreaterthananyfinite.
We,today,canunderstandthisdifference,butweforgetaboutitorignore
itmostofthetime.Euclidsaythat“foranygivennumberofprimenumbers
thereisalargerone.”Wesaythatthesetofprimesisinfinitewithoutpaying
muchattentiontothefactthatinthiswayweintroducenewentity,theactu-
allyinfinitesetofprimes.Ifitweren3tforthefactthatwedonotfearinfinity
becauseofourlackofsensivity,alackacquiredovercenturies,wemightenjoy
thislackoffearoftheinfinite.Inadditiontohavinggottenridofthefearofthe
infinitewehavealsogottenridofthefearoftreatingspaceasasetofpoints
andtimeasasetofmoments.Hencetheaporiaoftheflyingarrowdoesnot
reachourimaginationswiththeacutenesswishwhichitreachedtheimagina-
tionsoftheancients.Thislackofsensitivityisoneoftheclearlyperceivable
characteristicsofthemathematicsofourtime.
Ithinkthat1likeZenobeforehim1Aristotlewantedtoprojectthelogi-
calcontradictionwhichwouldpresumablyappearifweadmittedinourreason-
ingtheactualdivisionofthecontinuumintopoints.Wenowknowthat,from
alogicalpointofview,thisargumentdidnotsuffice;weknowthisbecause,
followingDedekind,wecanbuildcontinuamadeupofpointsandcanevengive
themthestatusofnumbers.ButwethinkthatforAristotleandhiscontempo-
rariesthedifficultiespresentedintheirreasoningswereenoughofadeterrent
tomakethemabandondoubtfulnotionsandtoadoptotherconventions.
Aconsequenceofthisstepwastheexclusionofthescienceofmotion
fromrigorousmathematicalarguments.Greekmathematicswasbydefinition
static.AristotlewroteinMetaphysics:“Itisasciencedealingwithmotionless
existences.”8EuclidleftussuchamathematicsinhisElements.
Euclidgeometrydealswithstraightlinesandcircles.Butapointdoesnot
moveonacircle.Nordoesitmoveonastraightline.True,thereissuperposition
ofsegmentsbutthisisaone-stepactivityratherthanapointbypointactivity.
Asimilarremarkappliestoarotationthroughadefiniteangle.
7Arystoteles,Fizyka,p.91.TranslatedbyAbeShenitzer.
8Arystoteles,Metafizyka[Metaphysics].Warszawa1985,p.284.TranslatedbyAbeShen-
itzer.
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