Why Stars Have No Feet- Explanation and Teleology in Aristotle’s Cosmology

7/25/2019 Why Stars Have No Feet- Explanation and Teleology in Aristotles Cosmology

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2009087. Bowen-Wildberg. 10_Leunissen. proef 1. 3-7-2009:11.22, page 215.

WHY SARS HAVE NO FEE:EXPLANAION AND ELEOLOGY IN

ARISOLES COSMOLOGY

M E.M.P.J. L*

.Introduction: Te scarcity ofteleological explanations in theDe caelo

Te most central eature o Aristotles conception o natural science ishis theory o natural teleology: everything that exists or comes to beby nature comes to be or changes, unless prevented, or a purposeand towards an end, and is present or the sake o that purpose orend. In the De caelo, which contains in the rst two books Aristotlesproblem-oriented exposition o his cosmology, traces o this teleologicalworldview are abundant. Te nature o the elements is claimed to be suchthat it provides them with an immanent capacity to exercise their specic

motions to reach their natural places. Lef to their own devices, the oursublunary elements would naturally move to their natural places and thusconstitute our separate, concentrically arranged spheres.1 eleology alsopermeates the heavenly domain o the stars and planets, as all celestialmotions are said to be trying to reach the most divine principle as anal cause (De caelo., b).

Although teleology as a natural tendency is thus without doubt animportant part o the makeup o Aristotles cosmology and celestialphysics, his general reliance on teleology toexplainthe different motionsand eatures o the heavenly bodies seems to be limited in comparisonwith the other physical treatises. For the whole o the De caelocontainsonly seven instances o explicit teleological explanations o cosmologi-cal phenomena, six o which are in the second book (there is only one

* Washington University in St Louis.1 Bodnr and Pellegrin () . For the teleological motion o the element earth

and or the notion o natural place as end, see the contribution by Matthen () in thisvolume (especially sections and ); or Aristotles account o the elements inDe caelo. and , see Gill (), especially section XX on elemental natural motion.


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instance o teleological explanation in book one, there are none in booksthree and our).2 Moreover, with one exception (De caelo., a),none o these explanations reer directly to nal causes. Instead, theyall proceed through the supposition o teleological principles, such asnature does nothing in vain, which in biology are only applied in veryspecic explanatory contexts, namely, in those cases where the discov-ery o nal causes is relatively difficult.3 Tis suggests that teleology isnot readily discernible in the case o the heavens. Aristotles use o tele-ological principles is all the more remarkable, because the teleologicalexplanations are the only ully-fledged physical explanations that Aristo-

tle offers in this treatise. By this I mean that the teleological explanationsare the only explanations in De caelo that address the nature andcauses o the various eatures and motions o the heavens and that buildupon some evidence rom observation. Aristotles cosmological treatiseconsists or the most part o statements o act and o arguments build-ing upon mathematical or numerical principles, which mainly addressthe number, shape, and possible motions o the heavenly bodies.4

2 For the teleological explanations and the principles used, see (a) De caelo .,a: Why is there no motion contrary to that in a circle? (teleological principle:nature does nothing in vain); (b) ., a: Why is there a plurality o motionso the heavens? (teleological principle: everything that has a unction is or the sake o

that unction); (c) ., a: Why do the heavens move in the direction they do?(teleological principle: nature always does what is best among the possibilities); (d) .,a: Why do stars not move on their ownor why have stars no organs or motion?(teleological principle: nature does nothing in vain); (e) ., a: Why do stars notmove on their own or why is there no harmony o the spheres? ( teleological principle:nature does nothing in vain); () ., b: Why do stars not move on their ownor why stars do not have a shape t or locomotion? (teleological principle: nature doesnothing in vain); (g)., ab: Why is there a difference in the complexity o themotions o the different heavenly bodies? (teleological principle: actions are or the sakeo something and the analogy with motions o sublunary beings).

3 eleological principles in Aristotles biology are generalizations pertaining to theobserved actions o actual and particular ormal natures o living beings, indicatingwhat nature always or never does in generation. It is my contention that propositionalprinciples o explanation, suchas Aristotles teleological principles, unction as the rame-work within which the explanation needs to take place (they both limit the amount andkinds o explanations possible, and license the explanations actually given) and are onlyused where reerences to nal causes are not immediately possible. Outside the rame-work set up by such principles, explanations lose their explanatory orce and ail to makesense altogether.

4 Bolton () calls this second type o arguments dialectical; see in particularsections and . o Boltons contribution to this volume. According to Bolton, thedialectical arguments in the De caelo rely on mathematical, numerological, or evenmythological starting points rather than on perceptual phenomena, and they establishonly what is reasonable () rather than what is necessary and true. While I agree


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Te purpose o the present paper is to shed light on the specicnature o the teleological explanations in Aristotles cosmology and onthe problems related to their application within this particular branch othe science o nature.5 In particular, I shall argue that the way in whichAristotle uses teleological principles to explain heavenly phenomenabuilds upon their very successul usage in biology,6 and is thus consistentwith his treatment o cosmology as a natural science. In section , I shallsay more about the scientic status o cosmology. Next, in sections and, I shall discuss two representative examples o teleological explanationsrom the second book o theDe caelo.

.Cosmology as science of nature

Te approach to the study o the heavens taken by Aristotles predecessorsand contemporaries had predominantly been mathematical in nature. (Inthe De caelo, Aristotle reers to them as mathematicians concerned with

with Boltons analysis o the nature o the bulk o the arguments used in the De caelo,I do not believe thatallarguments in it are dialectical. I submit that a minority o thearguments, i.e., the teleological ones, are not dialectical, but scientic in nature. Teteleological arguments lay out explanations that are proper to the natural sciences and

make useo principles that are rmlygrounded in theempirical evidence o thesublunarydomain. Te act that the heavenly domain is empirically underdetermined limits theexplanatory orce o these explanations (hence Aristotles warning that the explanationswhich he will offer are at most reasonable), but this does not mean that the explanationsthemselves are not scientic (): rather, they generate the best causal accounts othe eatures and motions o the heavenly bodies that Aristotle can offer.

5 Te issues that I should like to discuss in this paper have received relatively littleattention in the scholarly literature on Aristotle. Scholars who have studied teleology inAristotles cosmologyhave ocused almost exclusively on the role o the Prime Moveras anal cause in AristotlesPhysicaandMetaphysica. See, in particular, Kahn (). Otherstudies on cosmology have either lef out the question o teleology completely (Falcon), or have subsumed it under the normal use o teleology (Johnson ). On theother hand, Leggatt, in his commentary on De caelo, claims that Aristotle consciouslyplayed down the role o teleology in his cosmological treatise, because o his allegeddissatisaction with the type o intentional and psychological teleological explanationsdeployed byPlato in the imaeus: see Leggatt (), , . Hence, Leggatt offerslittle analysis o the teleological explanations actually provided in this treatise, because hebelieves them to be o little importance.

6 Te possible relative chronology o Aristotles works (according to which the Decaelois an early work and the biological works are late) does not affect my claim: sincenone o these treatises were published during Aristotles lie time, he may well haveadjusted and revised them continuously in the light o new discoveries or conceptualdistinctions made. For a deense o this view (based on a pedagogical interpretation othe cross-reerences in Aristotle), see Burnyeat () .


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where is best rendered by astronomyor simply as mathematicians.)7 Te theory reportedly put orward byEudoxus and revised by Callippus represented the apparent motionso the stars and planets as outcomes o systems o concentric rotatingspheres. Tis theory as reported did not explain the physical mechanicsand causes underlying those motions, perhaps because neither Eudoxusnor Callippus was concerned with those issues. In Phys. ., ba, Aristotle distinguishes this theoretical manner o studying theheavens () rom the proper study o nature by pointing outthat astronomerslike mathematiciansdo not study the properties o

bodiesquaproperties o those bodies, butquaseparable rom them.8

For Aristotle, however, just as or Plato, the study o the heavens ispart o the investigation o nature,9 and thus the heavenly bodies andtheir eatures will have to be studied in a manner that takes their naturesully into accountnature both in the sense o orm and o matter. Tisphysical approach to the study o the heavens is evidenced, or instance,in Aristotles claim that each o the spheres in his system is corporeal, andthus not simply a mathematical construct (De caelo., a):

.

For each sphere is some kind o body.

Tereore, i or Aristotle cosmology is part o the science o nature,and i scientic knowledge involves the knowledge o all our causes,10 amerely mathematical approach (such as avored by the astronomers andby Aristotle himsel in many o the arguments in the De caelo) will notbe sufficient to generate complete knowledge concerning the heavens,or the ollowing reasons. By its very nature, mathematical reasoningcannot yield understanding o nal causes (there are no nal causes

7 SeeDe caelo., a ( ; what themathematicians sayin astrologia also testiesto this), ., ab; ., a.

8 C.Meta. .,ba; ., ba and .,bawhereAristotle describesas not dealing with perceptible magnitudes or with theheavens above. C. SimpliciusIn phys. ., . (on the Greek conception oas being part o mathematics, not physics); Mueller () .

9 Aristotle emphatically introduces his study o the heavens as a part o the study onature: see or instance De caelo ., a ( ), ., b ( ), andMeteor. ., a.

10 See e.g.Phys. ., a, b;An. post. ., b and ., a: c. also Falcon () .


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in mathematics, because there is no change or good in that domain). 11

Hence, astronomy only yields understanding o the shape and size o theheavenly bodies, and o their distances rom each other and rom theearth. Tis gives important inormation about the quantitative propertieso the heavenly bodies and their motions, especially i combined witharguments drawing rom principles o physics. However, as a naturalphilosopher, Aristotle is also interested in the nature o the heavenlybodies, in their material composition, and in the causes o their motions(i.e., in their material, ormal, efficient, and nal causes). Te openingwords o theDe caeloare signicant:

, ,

Te science o nature is patently concerned or the most part with bodiesand magnitudes, the affections and motions o these, and urther, with allthe principles that belong to this kind o substance. (., a)

Because the natural sciences are concerned with all our types o causes,and especially since the understanding o nal causes is crucial (becausethe natural sciences are concerned with things that undergo change),Aristotle needs an additional strategy to extend scientic knowledge ashe understands it to the domain o the heavens. Tis strategy involvesthe application o teleological principles o the sort he employs in hisbiology precisely as a heuristic or nding nal causes where they are notimmediately observable. In short, Aristotle uses teleological principlesto discover purposes and unctions among the heavenly phenomena,and thereby tries to turn his study o the heavens into a proper naturalscience.12

11 Meta. ., ab.12 Aristotles treatment o cosmology as part o the study o nature also explains

why the teleological explanations are mainly ound in the second book o the De caelo.For it is this book that deals most specically with the heavenly bodies quasubjectso motion, that is, with the plurality, direction, and complexity o their motions, thephysical mechanisms underlying those motions, and the shape o the heavenly bodiesrequired to perorm those motions. On the other hand, we nd no teleological accountsregarding Aristotles views on the nature o the heavens as a whole (or instance, or sucheatures as the heavens size, uniqueness, or eternitytopics that are dealt with primarilyin book I), or regarding the motions and eatures o the our terrestrial elements (dealtwith in books ), which are not part o cosmology properly speaking. Aristotles useo causal language in the De caeloalso reveals that the second book is more concernedwith Aristotles own attempts to provide physical explanations than any o the otherbooks: o the occurrences o the term in the whole o the De caelo, can


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For Aristotle, scientic research comprises two stages o enquiry: therst stage consists in the systematic collection o observations o the phe-nomena, and the second one in the attempt to detect correlations and togive causal explanations o the phenomena. However, as Aristotle makesclear several times in theDe caelo(see his introductions to teleologicalexplanations discussed below in section ), it is not at all an easy under-taking to give physical explanations o cosmological phenomena. Tecentral problem is the limitednessor even lacko empirical evidence:the observations o the heavens we have are too ew, and the objects oobservation are too ar away to offer any certain evidence.13 Te only

observation that seems to be rock solid is that o the rotation o the heav-ens (De caelo., a -: we see the heavens turning about in a circle). Notwithstanding themany methodological caveats we nd inDe caelo(I shall discuss themin section below), Aristotle remains condent that it is still possible togive explanations o cosmological phenomena that go beyond the mereact that heavens rotate, and also beyond the conclusions (mathemati-cal or numerical) that reasoning yields about numbers, sizes, shapes, anddistances, or instance.

My contention is that Aristotles use o teleological principles, by anal-ogy with their use in the biological domain,14 orms an important part

o his strategy to increase the possibility o gaining scientic knowledgeo the heavens. Tus, when Aristotle does proceed to give physical orscientic explanations, he is unremittingly teleological in his approach.Te explanations thus presented will not qualiy as demonstrations in astrict sense (i.e., not as demonstrations as described in Analytica poste-riora or De partibus animalium),15 because they do not set out to demon-strate the truth but merely the reasonableness o certain causal scenar-ios. However, they go a long way in taking away some o the puzzlement

be ound in book (as opposed to in book , in book , and in book ), and othe occurrences o the term, can be ound in the second book (as opposed tonone in the rst and the third book, and in the ourth), while the reerences to causesand explanations in the ourth book are ofen (i.e., in ., a; ., a, a,a and a;., a)although not exclusivelyused in descriptions o viewsentertained by Aristotles predecessors.

13 C.Meteor. . andAn. pr. ..14 PaceFalcon () , who argues that Aristotle is reluctant to extend the results

achieved in the study o plants and animals to the imperishable creatures populating thecelestial world.

15 C. Lloyd () .


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pertaining to the heavenly realm and thus in making sense o the heav-enly phenomena. And as Aristotle has indicated elsewhere,16 makingsense in such difficult circumstances entails giving an account o theheavens that is ree o impossibilities.

Let us nally turn to some examples o the actual teleological expla-nations Aristotle provides in the De caelo. Broadly speaking, Aristotlegives two kinds o teleological explanations. Te rst kind consists oexplanations that stand on their own (that is, they do not orm part oan interrelated sequence o arguments), and set out to explain the pres-enceo certain eatures and motions o the heavens. 17 In these cases (i.e.,

.,a; ., aand ., ab),Aristotleexplains thepresence o some observed act by reerence to the good it serves withinthe heavens as a whole. Te basic teleological idea is that whatever canbe seen to be present, must be there to serve some good.

Te second kind consists o those teleological explanations that ex-plain theabsenceo heavenly eatures (this kind is used in ., a; ., a; ., a and ., b). Tey usuallyollow afer a series o mathematical or numerical arguments ollowingthe style o the astronomers. While the latter point out that it is, orinstance, mathematically impossible or some motion or eature to bepresent, the teleological explanation is set up to provide a counteractual

argument claiming that those motions or eatures in reality could notexist in the heavenly realm, because i they did, they would be in vain.Te teleological principle invoked in all o these cases is that nature doesnothing in vain.

In the next two sections, I shall discuss an example rom each group.

.Explaining why there is aplurality of motions of the heavens (Example )

Te rst example o a teleological explanation that I should like to discusspertains to the plurality o the heavenly motions: different heavenlybodies are observed to move in different directionswhy is it that they do

16 Meteor. ., a: We consider a satisactory explanation o phenomena inac-cessible to observation to have been given when we reduce them to what is possible.

17 Evidently there are no teleological explanations o the generation o the heavenlybodies as they are eternal and not generated. Cosmological teleological explanations arethus naturally restricted to the explanation o the eatures and motions belonging (or notbelonging) to the eternal heavenly bodies.


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not all move in the same direction? Aristotle introduces his explanationas ollows (De caelo., a):

, , -, , . . .

Since there is no motion in a circle contrary to motion in a circle, we mustexamine why there are severallocomotions, thoughwe must try to conductthe inquiry rom ar offar off not so much in their location, but rather

by virtue o the act that we have perception o very ew o the attributesthat belong to them [i.e., the motions]. Nonetheless, let us speak o thematter. Te explanation concerning these things must be grasped rom theollowing [considerations].

Tis text shows that Aristotle is very well aware o the act that it isproblematic and difficult to offer explanations o what is present in theheavens, given the lack o empirical evidence: we are simply too arremoved rom the objects o inquiry in distance.18

It is signicant that Aristotle is nevertheless condent that there isa way o answering this particular question, and that this answer ol-lows rom a teleologicalconsideration. As we will see shortly, the con-siderations rom which the explanation must be grasped is the sup-position o the teleological principle that everything that has a unc-tion must exist or the sake o that unction. By positing a teleologi-cal principle and, hence, by setting a ramework within which one cansearch or the possible unctions o those very eatures that have been

18 C. Burnyeat () , who observes that De caelo contains an unusuallyhigh number o occurrences o words like and which express epistemicmodesty: this or that is a reasonable thing to believe. I should like to add to thisobservation that words o epistemic modesty are even more abundant in book wherethe explanation o the presence and absence o heavenly eatures properly speaking isat stake (I counted only two occurrences o the word and none o the word in De caelo ; in De caelo , I counted occurrences o the word and two o the word). On the signicance o words like and cognates,see also the contribution by Bolton () in this volume. Note also that Bolton readsdisclaimers like the one quoted above as marking the inerior dialectical argumentsAristotle provides throughout De caelo (see in particular section .). In my reading,these introductions indicate that Aristotle, afer having offered dialectical or astronomy-style arguments earlier, now intends to offer genuine physical or scientic explanations,but that they will necessarily be o a weaker kind and, hence, only amount to what isreasonable.


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observed, one might be able to nd the explanation o why those ea-tures are present. On the other hand, the implication also seems to bethat this kind o knowledge cannot be gained by other means: observa-tion is certainly ruled out (observation in this case will only yield knowl-edge o the act that there are several motions, not o the reason why),but also mathematical arguments are not what is called or in these situ-ations, again because they cannot yield the reason why there are severalmotions.

Interestingly, the other two teleological explanations that stand ontheir own and explain the presence o heavenly phenomena are also

immediately preceded by a discussion o the methodological problemsrelated to this very enterprise o providing explanations in the strongsense or phenomena at such a remove (seeDe caelo., ba;., b and a). In all these methodological introduc-tions, Aristotle expresses his conviction that, even though the empiricalevidence is scanty, it is still possible to state the phenomena; and thatgiven all the limitations, the explanations offered are the best ones pos-sible.19 Te explanations that ollow these introductions are all teleolog-ical in nature, which shows that Aristotle has strong condence in theexplanatory orce o teleology also in these difficult cases.20

Returning to our example romDe caelo., the teleological principle

rom which the explanation o why there are several locomotions o theheavens must be grasped, is the ollowing (De caelo., a):

, , .

Each thing that has a unction is or the sake o that unction.

19 PaceGuthrie () .20 Tis point is also made by Lloyd () , with regard to the explanations in

De caelo . and .: Tus it is surely signicant that both on the problem o whythe heavens revolve in one direction rather than in the otherin .and on thedifficulty o the complexities o the motions o the non-xed starsin .his positivespeculations invoke teleology. I disagree, however, with Lloyds interpretation o thesignicance o this connection between Aristotles methodological disclaimers on theone hand and his use o teleology on the other. According to Lloyd () , ,, , Aristotles main interest in cosmology ollows rom his concern to establishhis teleology, and especially the orderliness o the heavens. However, I do not believe thatAristotles epistemological hesitations are not genuine here, or that Aristotles concernor the establishment o teleology is all that prominent in the De caelo. On the contrary,I believe that Aristotle uses his teleology, already rmly established on the basis o theabundance o empirical evidence discussed in his biological works, to extendwherepossiblehis knowledge o the heavens.


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Tis is a common principle in Aristotles biology (see, e.g.,De part. an.., b), where it is claimed that each part o the body is or thesake o the perormance o some unction. By stating it here, Aristotlemakes explicit that in his view, teleology extends to the heavenly domainand, hence, that some o the puzzling cosmological phenomena can beexplained by reerence to teleology. Aristotle also mustreer to teleologyhere, since material causes alone cannot account or the differences inlocomotions in the heavens (or all spheres are made rom the samematerial, which is aether).21 Te assumption that everything that hasa unction is present or the sake o that unction allows a series o

inerences that ultimately yield the explanation o why there are severalmotions o the heavens: i this principle applies, then each o the motionsmust serve its own unction.

Aristotle continues his explanation by identiying the unction o therst motion, in the ollowing way (De caelo., a):

. 22 . ( ), , .

Te activity o god is immortality, and that is everlasting lie. In conse-quence, it is necessary that eternal motion belongs to the divine. Since theheavens are o this sort (or this body is a divine thing), or that reason the

heavens have a circular body that moves naturally in a circle orever.

Te reasoning is that, i the unction o the divine is immortality, andi the heavens are divine, then the unction o heaven is immortality.Furthermore, i being immortal is the dening unction o heaven, then itis a necessary prerequisite or it to possess an eternal motion. Tat is, orheaven as a whole to be able to perorm its dening unction or its activityo being immortal, it has to perorm at least one kind o eternal motion.And the only kind o motion capable o uniorm eternal continuity ismotion in a circle.

Tis explanation, curious as it may sound, resembles a particular typeo explanation that Aristotle requently offers in his biological works.

21 C. Simplicius (quoting Alexander),In de caelo.: it is not possible to makeeither natural or material necessity responsible or these things, since both spheres havethe same matter, but it is necessary to give an account o the difference in terms o somedivine governance or ordering. For an analysis and deense o Aristotles arguments orthe existence o aether, see Hankinson () in this volume.

22 Here I ollow Leggatt in reading instead owith most manuscripts: seeLeggatt () . I believe Aristotles argument to be that the celestial sphere is likeadivine being in the sense that both partake in eternal motion, not that it itsel is a god.


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Consider the ollowing example taken rom De partibus animalibus,where Aristotle provides an explanation o why birds have wings (.,b):23

, . . . . .

For the substantial being o the bird is that o the blooded animals, but atthe same time it is also a winged animal, . . . and the ability to fly is in thesubstantial being o the bird.

Aristotle takes the essence, or the substantial being o the animal, as a

starting point, and derives rom this essence the necessary prerequisiteso something being what it is. Just as birds must have wings because theyare essentially flyers (and the only way or birds to perorm their deningunction is by using their wings), so toothe heavens must have a sphericalbody and move eternally in a circle because they are essentially immortal.According to this argumentation, eternal motion in a circle is the properattribute o an immortal body such as the heavens.

However, Aristotle has not yet explained why there are severalmotionso the heavenly bodies. Te second part o the explanation o why thereare several motions consists o a complicated chain o arguments, basedon a total o six assumptions. Te starting point o this chain is the

conclusion o the rst part o the explanation, which is the necessity othere being an eternal motion o the outer sphere in order or the heavento be immortal. Te reasoning Aristotle employs is deductive, but thetype o necessity to which Aristotle reers is sometimes that o a necessaryconsequence, while at other times it is the necessity o something havingto be present rst i something else is to be present (the latter is whatAristotle calls conditional necessity).24 Let me give a summary o thechain o arguments (De caelo., ab):

(a) I there is to be a body that moves in a circle eternally, it must have acenter that remains at rest.

(b) For there to be a xed center, the existence o the element earth is

a necessary condition (i.e., since whatever is made o aether cannot

23 C.De part. an. ., b and ., b. For my analysis o the structureo this type o teleological explanation, see Leunissen () .

24 Te ormula . . . is repeated six times: in De caelo ., a;a, and b (see (a), (b), and () above), the necessity is conditional; in a,a, and a (see (c), (d), and (e) above), the necessity indicates a necessaryconsequence.


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remain at rest, there must be a second element next to aether, thenatural motion o which is to move towards the center and then toremain at rest in the centre).

(c) I there is to be earth, then it is a necessary consequence that thereis also re (or earth and re are contraries, and i the one exists, sodoes the other).

(d) I there is to be re and earth, then it is a necessary consequence thatthe two other elements exist (or water and air are in a relation ocontrariety to each o the other two elements).

(e) From the existence o the our elements, it necessarily ollows that

there must be generation (or none o the our sublunary elementscan be everlasting).

() I there must be generation, then it is necessary that there exists someother motion.

According to this account, generation is a necessary consequence o therebeing sublunary elements, whose existence is a necessary condition orthere to be an eternal, cyclical motion o the outermost sphere o theheavens carrying the xed stars. However, having established that it isnecessary or there to be generation (as a consequence o there beingthe our sublunary elements), Aristotle turns the argument around, and

reasons that i there is to be generation, then it is conditionally necessaryor there to be other motions, because the motions o the outermostsphere alone cannot cause generation. Accordingly, generation is thator the sake o which all the other motions (namely, the motions o theplanets) take place. Tis is how Aristotle summarizes his explanation (Decaelo., b):

, , , , , , , .

For the moment so much is clear, or what reason there are several bodiesmoving in circles, namely, because it is necessary that there is generation;and (because) generation (is necessary) i there also has to be re; and(because) that one and the others (are necessary) i there also has to beearth; and (because) that one because it is necessary that something alwaysremains at rest, i there has to be something that is or ever in motion.

Te complete explanation o why there are several motions o the heav-ens is thus that there are several unctions or the sake o which thesemotions are present. Tere is one eternal motion in a circle (perormed


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by the outer sphere carrying the xed stars) or the sake o realizing theimmortality o the heavens, and there are other motions (perormed bythe inner spheres carrying the planets) or the sake o generation.

Here, the use o the teleological principle allows Aristotle to draw anorganic picture o the cosmological system in which all the observedmotions can be explained by the purpose they serve. Arguably, thispicture and the type o reasoning behind it are not without problems,25

but at least Aristotle is able to give some rationale or some phenomenathe astronomers did not explain. Te plurality o the motions o theheavenly bodies makes sense in the light o the need or the heaven as a

whole to perorm an eternal motion, i it is to be truly immortal, and as acorollaryo the need or there to be generation, i this eternal motion isto be at all. In sum, thelack o empirical evidencemakes it hard to provideully-fledged physical explanationsin cases like these, butthroughthe useo teleological principles that are well established in his biology Aristotleat least succeeds in mitigating some o the perplexities pertaining to someheavenly phenomena.

.Explaining why stars have no feet (Example )

I shall now turn to an example o the second type o teleological expla-nations, where Aristotle uses some orm o the teleological principle thatnature does nothing in vain in order to explain the absenceo heavenlyeatures, usually afer a series o mathematical arguments or discussionso the available empirical evidence.

Teexplanandumto be discussed concerns the question whether ornot the stars and planets possess a motion independently o the motiono the spheres. One explanation is given in chapter .. Ultimately, thepurpose o the chapter is to show that the heavenly bodies (most likely)do not possess a motion o their own, but are carried around xed inconcentric spheres.26 First, Aristotle sketches three possible scenariosconcerning the motions o the heavenly bodies and their spheres (Decaelo ., b). As both are observed to move as a whole, it is

25 For instance, it does not establish an explanation oreacho the individual motionso the planets, or or the need or there to be generation. Tis latter point is well broughtout (along with others worth noting) by Hankinson () .

26 Te basic idea is that i the stars possessed their own motion, they would be sel-movers; and this would make them in principle able to stop their motions, which wouldthreaten the eternity o the heavens and lie as we know it.


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necessary that the change o position takes place with both the heavensand the stars being at rest, or with both moving, or with the one movingand the other at rest. Aristotle then reers to empirical evidence (Decaelo ., b , b)and gives mathematical arguments (., b ) in order to show that the scenario in which the spheresmove while the heavenly bodies are at rest is the least absurd (.,b ). In addition tothis, Aristotle offers a nal teleological argument in avor o this theory,arguing or the unlikelihood o the stars and planets possessing a motion

on their own. Te argument runs as ollows (De caelo., a):

( ), , , , .

In addition to these arguments, it would be absurd that nature gave themno organ or motion (since nature does nothing as a matter o chance),and that she should care or animals, but disregard such honorable beings;rather, it seems that nature, as though deliberately, has taken away every-thing by means o which they might possibly in themselves have effectedorward motion, and that she set them at the greatest distance rom those

things that possess organs or motion.

In a way, Aristotles explanation here parallels that o Plato in the imaeus(da). In this dialogue, imaeus explains that the divine crafsmandid not think it necessary to equip the heavensel-sufficient and perectas it iswith hands or eet or walking:

. , , , . , ,

. .

For he thought that a being which is sel-sufficient would be much betterthan one which is in need o other things. And he did not think it was nec-essary to attach hands to it to no purposehands or which there wouldbe no need either to grasp or to deend itsel against anything; nor had itany need o eet, nor o the whole apparatus o walking. For he assignedto it the motion that is most suited to its body, [the motion] which, o the


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seven, is the most appropriate to mind and to thinking. And, thereore, hecaused it to move in the same manner and on the same spot and revolvingin a circle within its own limits. All other six [motions] he took away andit was made not to partake in their deviations. And as this circular motionrequired no eet, the universe was created without legs and without eet.

In this passage, Plato describes how the heaven was created and wasgiven its circular motion, which is most appropriate or its sphericalshape. Te other types o motionorwards/backwards, to the lef/tothe right, and up/downwere taken away rom it (im. a).However, instead o this mythological account or why the stars have no

eet, Aristotle opts or a naturalistic explanation.Te structure o Aristotles argument is quite complex. In short, it con-

sists o areductio ad absurdumollowed by an alternative account pro-claiming the purposiveness or, perhaps even the providence, o nature.Te rst part o the argument builds upon the implicit counteractualassumption that i the stars were intended by nature to be moving ontheir own, it would be absurd or nature not to have given them organsor motion, given the act that nature did provide such organs to lesserbeings. I take the expression that nature does nothing as a matter ochance to be equivalent to the principle that nature does nothing in vain:living beings always have the parts that they need, and i the heavenly

bodies lack organs or motion, that lack must be or the sake o some-thing; or, to put it the other way around, i the organs or motion areabsent in heavenly bodies it must be because their presence would havebeen in vain (they would have had no unction to ulll in this particularkind o being). Te reerence to the honorable status o heavenly beingsimplies that Aristotle takes the teleology o nature to apply evenmoretothem than to the sublunary beings.27

27 Aristotlerepeatedly offers the a fortiori argument that i one agrees that animals andplants neither come tobe nor exist byspontaneity (butor thesake osomething),thentheclaim that spontaneity is the cause o the heavenswhich is most divine and exhibits thegreatest ordermust be absurd, and that one has to conclude that nal causality pertainsto the heavenly realm as well. See Phys. ., ab; . a and De part. an.., b and b:

Tis is why it is more likely that the heavens have been brought into being by sucha causei it has come to beand is due to such a cause, than that the mortalanimals have been. Certainly the ordered and denite are ar more apparent in theheavens than around us, while the fluctuating and random are more apparent inthemortal sphere. Yet some peoplesay that each o theanimals is and came to be bynature, while the heavens, in which there is not the slightest appearance o chanceand disorder, were constituted in that way by chance and the spontaneous.


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....


Te implicitunderlying teleological principle here is that each capacity(in this case the capacity to locomote) requires an organ28 and that thuslocomotion o the stars is possible i and only i they have organs or loco-motion. Te absurdity lies in the act that nature didprovide less honor-able beings with organs or motion, and that we would have to conclude,were we to accept this account as true, that nature purposely neglectedmore honorable beings such as the stars. Since this account is o courseunacceptable within Aristotles viewo the way nature operates, the oppo-site scenario, set out in the second part o the argument, must be the case:nature hastaken awayevery means o locomotion, and thereby set a dis-

tance between the heavenly bodies and the sublunary beings equippedwith organs or motion.29 As Aristotle explains, spherical bodies are leastt to effect orward motion on their own, because they lack points omotion (De caelo., b):

, , .

For orward motion it is least t, since it is least like to those things thatproduce motion on their own; or it does not have any appendage orprojection, as does a rectilinear gure, but stands most apart in shape romthose bodies equipped or locomotion.

Te core o this teleological argument or why the heavenly bodies donot have a motion o their own and, hence, must be xed in spheres,is thus the assumption (presented as a act) that heavenly bodies do nothave eet or any other organs or locomotion. For, i natureor the mostpartdoes nothing in vain and the heavenly bodies have no eet, then theconclusion is reasonable that nature must have designed the heavenlybodies not to be able to move on their own.

Te teleological argument that Aristotle offers here is again in manyways similar to explanations we nd in the biological works. In biology,Aristotle holds that all animals that are capable o locomotion must have

organs or motion

30

and that animals without organs or motion are not

28 De gen. an. ., a.29 Aristotle considers it to be better or the superior to be separated rom the inerior;

c.De gen. an. ., a, where Aristotle explains that it is better or the male and theemale to be separated, or it is better that the superior principle should be separatedrom the inerior.

30 De part. an. ., ab: all (animals) that walk must have two hind eet;De incessu, a: Tat which moves always makes its change o place by the


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capable o locomotion.31 Tese two laws are exhaustive with regardto all blooded land walkers. Te one and only exception to this rule isormed by the ootless snake,32 which obviously does not have organsspecically designed or locomotion, but moves orward by bendingitsel. Just as in our example concerning the heavenly bodies, Aristotleexplains the absence o eet by invoking the principle that nature doesnothing in vain (De incessu, a):

, -, , - . , , . ( ), .

Te reason why snakes are ootless is both that nature does nothing invain, but always, rom among the possibilities, picks what is best or eachthing, preserving the proper substantial being o each, and its essence; andurther, and as we have stated previously, none o the blooded animals canmove by means o more than our points. For rom these [two premises]it is apparent that none o the blooded animals that are disproportionately

long relative to the rest o their bodily nature, as are the snakes, can beooted. For, on the one hand, they cannot have more than our eet (sincein that casethey would be bloodless); and, on the other hand, having twoorour eet they would be pretty much completely immobileso equipped,their motion would necessarily be slow and useless.

In short, starting rom this principle, Aristotle offers the counteractualargument that i nature had equipped snakes with eet, snakes wouldmove very badly and the eet would have been next to useless. Given theprinciple that nature does nothing in vain (andthat nature cannot givesnakes more than our eet, since, in that case, the snake would not beblooded), snakes do not have eet.33

employment o at least two organic parts, one as it were compressing and the other beingcompressed.

31 De incessu, a: And so nothing that is without parts can move in thismanner; or it does not contain in itsel the distinction between what is to be passive andwhat is to be active.

32 De part. an. ., b;De incessu, b.33 However, theact that snakes do not have organs or motion does not mean that they

do not locomote: they move orward by bending themselves (see De incessu, b


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....


Tere is, however, an important difference between the explanatoryorce o the use o this principle in biology as opposed to its use in cos-mology, and this difference derives directly rom the lack o observationalevidence in the latter domain. For, in the biological domain observationdetermines the possibilities o what nature does and does not produce.34

In the case o the ootless snake, observation shows that all other bloodedanimals that live on land have eet; blooded land dwellers share to a cer-tain extent the same ormal nature, which explains the occurrence o cer-tain coextensive eatures like the possession o a maximum o our eet.Te snake also possesses all the properties that belong to blooded land

dwellers, except or one. It is thereore rational to ask why this partic-ular property is absent in snakes. It is not rational to ask why snakeslack wings, telescopic eyes, or any other part that cannot be observedto belong to the wider class to which snakes belong. As there is a vir-tual innity o properties that any animal does not have, it only makessense or a natural scientist to explain the absence o those propertiesthat belong to the natural possibilities o that animal; and what thosenatural possibilities are, can be established inductively, on the basis oobservation and through comparison with related beings.

In the cosmological domain, on the contrary, the range o possibleways in which a certain eature or motion can be present is only partly

determined by observation. What cannot be observed might still bepresent, and what can be observed might be the result o a visual illu-sion. Aristotle ofen struggles with this question o how much credencewe must attribute to our observations o the heavens, and o which obser-vations we should explain and which we should explain away. His gen-eral strategy is to explain the phenomena and hence to save them; buton occasion, especially when there are contradictory observations, theobservations that conflict with the thesis that the stars move around xedin concentric spheres are rather explained away. Tis is exactly what hap-pens in the paragraphs leading up to the explanation o why stars haveno eet in De caelo ., a. Beore giving his teleological argu-

; , ab; , b.).is the punctuation correct

Tis may point to a problem or Aristotles argumentconcerning the heavenly bodies: or the absence oorgansor locomotion as such doesnot provide conclusive evidence that the stars in act do not locomote. O course, as theremainder oDe caelo . points out, Aristotle is actually committed to thestronger claimthat spherical bodies do not only lack organs or motion, but also points o motion,which (at least given Aristotles laws o sublunary mechanics) rules out any possible wayo locomotion.

34 Lennox () .


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ment demonstrating the likelihood o the absence o eet in stars, Aris-totle argued that i the heavenly bodies were to move on their own, theywould either roll or rotate, but that neither o these motions is observedto take place. Te impression that the Sun rotates in rising and setting 35

is then explained away: according to Aristotle, the rotation is merely avisual illusion, caused by the weakness and unsteadiness o our vision.

What this makes clear is, rst o all, that while in biology observationsclearly show that snakes lack eet, observational evidence o the heavensgives much less certainty about the absence o eet in the heavenly bodies.For all we can tell, the heavenly bodies might be too ar away or us to see

their organs o motion. Secondly, observations o the heavens will nottell us whether there are anynaturallimitations to the possible ways inwhich nature could have crafed stars in order to make them able tomove on their own. Te absence o eet in the heavenly bodies in itselseems hardly enough to establish the reasonableness o the alternativetheory that they do not effect any orward motion at all.

Tis difference between the reliability and applicability o observa-tional evidence in biology and cosmology is important, because Aris-totles explanation in the case o the heavenly bodies is not promptedbythe observation that they do not have organs or motion, as it is in thecase o snakes.36 Tere are no observations o the heavens that would

reasonably lead to the expectation o heavenly bodies having eet inthe rst place. (One might object, however, that in this case the philo-sophical tradition within which Aristotle is working prompts this ques-tion).37 Rather, Aristotle works the other way around: because he wantsto make the theory that the stars do not move on their own as rea-sonable as possible, he uses the teleological principle that nature does

35 Xenophanes might have observed the same phenomenon, and gives it a similarexplanation: see Diels and Kranz () Aa -; [the Sun] seems to turn in a circle due to its distance.

36 InDe part. an., the principle is commonly used in the context o a discussion owhy animals have certain parts, where it is discovered that a certain kind o animallacks that part while other members o its larger amily or otherwise related animals haveit. Te question thus arises through comparative and empirical research. For examples,seeDe part. an. ., a and a; ., a and a.

37 On this tradition, see Cornord () ; besides Plato, Empedocles alsoseems to have argued or the ootlessness o the celestial sphere (Diels and Kranz, )B: , , . ,, (), , )

non-matching parenthesis.


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....


nothing in vain to argue or the likelihood o the absence o the organso motion in the heavenly bodies.38

In sum, it seems that in this example Aristotle goes out o his way toestablish the reasonableness o the assumption that the heavenly bodiesdo not have a motion o their own and, hence, must be carried aroundwhile being xed in concentric spheres. In the biological realm, theobservation o what happens always or or the most part in natureis what allows us to draw inerences about cases in which the goal-directedness is less evident. In a domain such as cosmology, whichis empirically underdetermined, such inerences are necessarily o a

conjectural nature. However, i teleology extends to the heavenly realm,and Aristotle assumes that it does, then the use o teleological principlesallowsAristotle to make the most sense o the phenomena, andto provideexplanations appropriate to the science o nature, rather than merelyastronomical or mathematical ones.

.Conclusion

o a modern audience, Aristotles teleological explanations o heavenlyphenomena may sound rather unusual, but what I hope to have made

clear in this chapter is that they make perect sense within Aristotles con-ception o natural science. I the heavens are part o nature, then we needat least to attempt to state all our causes or every heavenly phenomenon,even i the investigation has been made difficult because o the scarcity oempirical data. Aristotles use o teleological principles thus ollows romhis treatment o the study o the heavens as part o the study o nature;and we have seen that this approach is especially prominent in the sec-ond book othe De caelo, where Aristotle searches or explanations o theeatures and motions o the heavens as a whole and o the heavenly bod-ies. Te scientic investigation o an empirically undetermined domainsuch as the heavens is difficult, as his methodological reflections show,Aristotle is mostly well aware o all the problems involved. However, ione wants to gain knowledge o the heavens and its bodies, one has to tryto give explanations that at least make the phenomenaboth in terms owhat can and o what cannot be observedseem as reasonable as possi-ble.39

38 Aristotle repeats this argument in a reversed orm inDe caelo., b.39 C. Irwin () .


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Te strategy that Aristotle employs to give plausible accounts is to positteleological principles as a way o nding nal causes in difficult cases.Te principles used are not a priori axioms, but suppositions derivedrom empirical evidence. Tey are generalizations over the actions o theormal nature o beings, based on numerous observations made in thebiological domain. Just as the use o these principles helped Aristotle tond nal causes in cases where these were not immediately observablein biology, in the same way Aristotle hopes to nd explanations ornatural phenomena in the cosmological realm. Tis gives a very centralrole to Aristotles scientic practice in biology: one could say that where

Aristotles philosophy o science as described in the Analytica posterioraoffers the student o nature his scientic toolbox, the accessible and richdomain o biology is the students main workplace. Te experience andknowledge acquired in studying biological phenomena may thenocourse with suitable adaptations and renementsbe applied to other,less accessible domains o nature, such as that o the heavens.

Te application o teleological principles to the cosmological domainis itsel based on the assumption that the heavens are no less teleologicaland, perhaps even more teleologicalthan the sublunary realm is.However, as I have pointed out, the lack o empirical evidence in thecosmological realm also weakens to some extent the inerences that

Aristotle draws within this teleological ramework:40

the explanations areplausible, but not as conclusive as the ones we can nd in the biologicalworks.

For the De caelo this means that Aristotle argues as much rom astowards teleology: starting rom the assumption that the heavens as awhole are goal-directed, Aristotle tries to give a coherent, plausible, andreasonable picture o the heavens in which things are present or absentor a reason. Tis is Aristotles main goal in the De caelo: even i it is notpossible to give deductions that demonstrate why the heavens and theheavenly bodies have the eatures they have, one can still offer plausiblephysical accounts or inerences to the best explanation that take awaysome o the puzzlement concerning the heavens.

40 C. Falcon () ix: there are eatures o the celestial world that outrun theexplanatory resources developed by Aristotle or the study o the sublunary world.


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....


Acknowledgments

For ruitul discussions o preliminary drafs o this paper I thank Fransde Haas, Jim Hankinson, and Ineke Sluiter. Tis paper also owes much tothe questions asked and comments made by the audiences at the DutchGraduate School or Classics (OIKOS); the American Philological Asso-ciation, th Annual Meeting, Montreal; SUNY Albany; University oennessee, Knoxville; Wesleyan University, Middletown; and Washing-ton University in St Louis.

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Why Stars Have No Feet- Explanation and Teleology in Aristotle’s Cosmology

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Transcript of Why Stars Have No Feet- Explanation and Teleology in Aristotle’s Cosmology