Copernicus and Aristotle's Cosmos
Author(s): Henry Guerlac
Source: Journal of the History of Ideas, Vol. 29, No. 1 (Jan. - Mar., 1968), pp. 109-113
Published by: University of Pennsylvania Press
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COPERNICUS AND ARISTOTLE'SCOSMOS
BY HENRY GUERLAC
Few historians of science would reject the propositionthat the emergence of modern exact science in the seventeenth century required the
abandonment of Aristotle's structured cosmos, that nest of concentric
spheres sharply marked off into two contrasting regions: a "celestial"
region beyond the moon, and below it the spheres of the four elements. In
the higher region, the heavenly bodies, perfect and unchanging,made of
some aetherial substance or unearthly "quintessence,"move in eternal
circles of perfection; in the lower, the domain of "generationand corruption," the elements, when not at rest in their properspheres, move "naturally" only in straight lines: upward towards the world's circumference
(Fire and Air), or downward(Earth and Water) towards the center of the
immobile earth, the center of the universe. In short, the two regions differ
both in their material constitution and in their principles of motion; to
Aristotle these differencesmeant much the same thing.
To a large extent, the abandonmentof the older view resulted from
the growing conviction that between the earth and the celestial bodies
there had to be some similarity of substance, and that the same rules of
motion, the same physics, must apply in the heavens and on the earth.
This portentousintellectual shift was surely gradual; but the process was
undeniably completed, not only by Newton's day, but a half century or
more earlier when Descartes and the other mechanical philosophers set
forth their grand designs. Yet others, still earlier, must have paved the
way, men like Kepler, Galileo, and Copernicus.
What role in this transformationdid Copernicusplay? He used to be
credited with a substantial contribution,despite his much-discussed"conservatism"and his manifest debt to the older physics, for he transformed
the earth into a planet and placed it, between the paths of Venus and
Mars, in a circular orbit about the sun. This view of Copernicus,however,
has been challenged.In a long note that appearedin 1940 in the first issue
of this journal, the late Edgar Zilsel described in some detail the antiquated characterof the physics in the De Revolutionibus and wrote that
Copernicus"fully accepts the theory of Aristotle and classical astronomy
that celestial bodies move in circles and that this movement is something
'natural,' whereas rectilinear motion belongs only to terrestrial bodies. ...
1
More recently, ProfessorGerald Holton of Harvard University has deflated
the claim for Copernicusstill further. In a brilliant and influential article
he points to Kepler as the first of the moderns "to look for a universal
physical law based on terrestrialmechanicsto comprehendthe whole universe in its quantitative details."Well and good. But he goes on to remark
that in the schemes of Aristotle and Ptolemy, "and indeed in Copernicus'
own,"the planetsmove accordingto laws that are eitherpurelymathematical
"or mechanical in a nonterrestrialsense," by which he means, I suppose,
1E. Zilsel, "Copernicus and Mechanics," this Journal, I (1940), 113-118.
109
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110
HENRY
GUERLAC
the doctrine of crystalline spheres.2 With Kepler, however, this crucial
distinction, this celestial-terrestrial dichotomy, disappears for the first time.
Its abandonment, Professor Holton points out, is evident as early as the
youthful Mysterium Cosmographicum (1596) in which Kepler treats the
earth "as being an equal of the other planets," and employs "a single
geometrical device" to explain the observed arrangement of the planets
in their orbits about the sun.
But what of Copernicus, from whom Kepler learned this planetary arrangement? According to Holton, he could scarcely have played a role in
emancipating mankind from the older view, for in fact he clung to the
Aristotelian dichotomy:
As Goldbeck reminds us, Copernicus himself still warned us to keep a clear
distinction between celestial and merely terrestrial phenomena "so as not
to attribute to the celestial bodies what belongs to the earth." 3
The phrase that Holton put in quotation marks is derived-I use the word
advisedly-from the concluding sentence of the De Revolutionibus, Lib. I,
Cap. IV. It should be examined with some care, for on its interpretation
and proper rendering a great deal obviously hinges. If this is what Copernicus wrote, and if he intended by what he wrote what Professor Holton
claims he intended, then a serious problem arises, for such a statement is
hard to reconcile with what we know of the doctrines of Copernicus. Let
us examine the context in which that phrase appears, and look first at
two readily available English translations of the entire sentence. We may
begin with the rendering of C. G. Wallis in the Great Books of the Western
World, for Holton's quotation could well pass for an excerpt from it:
I think it necessary above all that we should note carefully what the relation of the Earth to the heavens is, so as not-when we wish to scrutinize
the highest things-to be ignorant of those which are nearest to us, and
so as not-by the same error-to attribute to the celestial bodies what belongs to the Earth.4
This is a reasonably accurate, if somewhat cumbersome, rendering of the
original; at least it is closer to the text than the free-wheeling version given
by Thomas S. Kuhn in his Copernican Revolution, where Copernicus is
supposed to have written:
2 G. Holton, "JohannesKepler'sUniverse: Its Physics and Metaphysics,"American Journal of Physics, 34 (1956), 340-351; reprintedwith correctionsin Robert
M. Palter, TowardsModernScience,2 vols. (1961), II, 192-217. This is the version
I cite in this paper (see especially pp. 195-196). Italics mine. The same material
appears in Holton's JohannesKepler et les originesphilosophiquesde la physique
moderne (Paris [Palais de la Decouverte], 1961), 8.
3 Palter, op. cit., 195. Holton's authority is Ernst Goldbeck,Keplers Lehre von
der Gravitation(Halle, 1896), (Abhandlungenzur Philosophieund ihrer Geschichte,
No. 6). Goldbeck'spaper is reprintedin his Der Menschund sein Weltbild (Leipzig,
1925), 185-239.
4 Great Books of the Western World, Vol. 16 (Ptolemy, Copernicus,Kepler),
(EncyclopediaBritannica, Inc., 1952), 514. I have italicized the words that correspondto Holton's citation.
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COPERNICUS AND ARISTOTLE'S COSMOS
111
It is therefore above all needful to observe carefully the relation of the
Earth toward the Heavens, lest, searching out the things on high, we should
pass by those nearer at hand, and mistakenly ascribe earthly qualities to
heavenly bodies.5
Both Holton's and Kuhn's citations are misleading: Holton's because
it is fragmentary, out of context, and seems to involve an unavowed ellipsis;
Kuhn's because it is very loose and quite gratuitously introduces the notion
of "qualities." A glance at the Latin suffices to reveal these inaccuracies:
Quam ob causam ante omnia puto necessarium, ut diligenter animadvertamus, quae sit ad coelum terrae habitudo, ne dum excelsissima scrutari
volumus, quae nobis proxima sunt, ignoremus, ac eodem errore quae telluris
sunt attribuamus coelestibus.6
Perhaps this passage could be satisfactorily rendered as follows:
For this reason, I believe it necessary above all for us to observe carefully
what is the relation (habitudo) of the earth to the heavens, so as not to
be unaware of those things that are nearest to us when we wish to examine
(scrutari) the highest things and, by the same error, to attribute to the
heavens what pertains to the earth.7
What, in fact, is Copernicus talking about? Surely he is not saying that
we must keep a "clear distinction" between the two physically different
domains because of that fundamental difference in their constitution which
Aristotle insisted upon. If anything, he seems rather to be saying the opposite: in the words that Holton omits, Copernicus is warning the reader
that to understand celestial phenomena one must somehow take the earth
into consideration. But in so doing we should not commit the error of
attributing something to the heavens that pertains, instead, to the earth.
But what is this "something"? Now if we attend to what precedes this
crucial passage of Cap. IV, and what follows immediately in Cap. V, the
answer is clear: Copernicus is talking about motion, real and apparent, and
about nothing else. Cap. IV in fact bears the heading Quod motus corporum
coelestium sit aequalis ac circularis, perpetuus, vet ex circularibus compositus (That the motion of the celestial bodies is regular and circular, perpetual, or compounded of circular motions). The discussion that ensues is
5Thomas S. Kuhn, The CopernicanRevolution (Cambridge,Mass., 1957), 147.
Italics mine. The translationis by J. F. Dobson and S. Brodetsky,OccasionalNotes
of the Royal AstronomicalSociety, Vol. 2, No. 10 (London, 1947). Kuhn, it should
be emphasized,does not draw the obvious conclusionfrom this passage; instead,
farther on (p. 152), in commentingupon Copernicus'discussionof rectilinearvs.
circularmotion in Cap. VIII, he correctlypoints out: "Copernicus'argumentshows
how quickly the traditional distinction between the terrestrial and the celestial
regionsmust disappearwhen the earth becomes a planet."
6 De RevolutionibusOrbiumCoelestiumLibri VI
(Nuremberg,1543), 3.
7 It was
tempting to translate Copernicus'word habitudo,as "aspect"-a familiar technical term in early astrology and astronomy-in order to suggest that
Copernicusis consideringthe optical relations,not physical ones, between the earth
and the celestial bodies. The emphasis on sight appears in Copernicus'choice of
the verb scrutari.
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112
HENRY GUERLAC
optico-geometrical; it deals with the irregular motions of the sun, the
moon, and the planets. Copernicus is preparing his reader for the possibility
that these irregular motions are only apparent, the result of viewing the
celestial bodies from an earth that may not be the center of their revolutions and may itself be in motion. If so, what we observe must be, in each
case, a compounded motion; it is therefore necessary to distinguish what the
appearances owe to the planets' own motion (a true circular motion about
some center other than the earth) and to the earth's own position and
motion, its habitudo, with respect to them. It is an error, therefore, to disregard the earth (quae nobis proxima sunt) when attempting to understand the celestial motions; an error "to attribute to the heavens what
pertains to the earth." 8
Surely the passage in question in no way yields what Goldbeck and
Professor Holton would draw from it; other evidence must be brought to
the bar if we are to charge Copernicus with wishing to "keep a clear distinction between celestial and merely terrestrial phenomena," 9 in the sense of
preserving the old dichotomy. But the available evidence points in a different direction. In the De Revolutionibus, Copernicus is at pains to stress
the resemblances between the earth and the planets: like the planets, the
earth is spherical; like them, too, it moves with circular motions; and it no
longer enjoys the unique distinction of resting at the center of the universe: like the planets, it is a body revolving about the sun.
Though his physics is archaic, and Zilsel supplied ample evidence for
this, Copernicus is by no means rigorously Aristotelian. In fact, he abandons Aristotle on the very point used to prove a dichotomized universe:
that different natural motions express the different "natures" of sub-lunary
matter and of the substance of the heavenly bodies. And, in a manner of
speaking, Copernicus foreshadows a unitary physics when he argues that
there is only one natural motion in the universe shared by the earth and
the celestial bodies: motion in a circle. Rectilinear motion is no longer the
natural motion of elemental bodies, nor peculiar to the sub-lunary spheres.
It is not the proper motion of any natural object, but occurs only when
such an object, whether terrestrial or celestial, is somehow removed from
its proper place."
8Cap. V begins with Copernicus'statement that one must discover whether
the earth is in motion and what is its place in the universe "sine quibus non est
invenire certain apparentiumin coelo rationem."
9 Holton in Palter, op. cit., 195.
10For Copernicus,an object's "properplace" is with the sphericalmass of its
own substance. His interesting theory of a plurality of gravitations (De Revolutionibus, Lib. I, Cap. 9) suggests that he was willing to ascribe the "unnatural"
rectilinearmotions to the material componentsof the planets, and not confinesuch
motions to the earth, as Zilsel believed (loc. cit., p. 116). Gravity, Copernicussuggests, is a natural desire (appetentia) given to the parts of a body to regain their
unity and completeness(integritas). This property (affectio) may be found in the
sun, the moon and each of the planets. There is thus a solar, a lunar, and a martial
gravity, in which displacedportions of solar, lunar or martial material return by
rectilinearpaths to their respective orbs.
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COPERNICUS AND ARISTOTLE'S COSMOS
113
Nothing, indeed, proved to be more subversive of the old divided order
than Copernicus' insistence on circular motion as the single natural motion
to be found in the universe. Galileo saw this clearly, and it must have
contributed, fully as much as some Neoplatonic or Hermetic predilection,
to his persistent and much-debated allegiance to circularity (and so to his
failure to accept Kepler's elliptical orbits). In his Dialogo, Galileo has
Salviati, his chief spokesman, point out to Simplicio, the hard-pressed
Aristotelian, that
none of the conditions by which Aristotle distinguishes celestial from elemental bodies has any other foundation than what he deduces from the
difference in natural motion between the former and the latter. In that
case, if it is denied that circular motion is peculiar to celestial bodies, and
affirmed to belong to all naturally moveable bodies, then one must choose
one of two necessary consequences. Either the attributes of generableingenerable, alterable-inalterable, divisible-indivisible, etc. suit equally and
commonly all world bodies-as much the celestial as the elemental-or
Aristotle has wrongly and erroneously deduced, from circular motion, those
attributes which he has assigned to celestial bodies.ll
From his point of view, Simplicio was quite right to protest: "This way
of philosophizing tends to subvert all natural philosophy, and to disorder
and set in confusion heaven and earth and the whole universe." 12 For this
is precisely what it did. Perhaps Copernicus was something of a revolutionary after all.
Cornell University.
11Galileo Galilei, Dialogue Concerningthe Two Chief World Systems, trans.
12Ibid.
Stillman Drake (Berkeley and Los Angeles, 1953), 37.
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