A Few Thematic and Dialectical Resonances between Capuano andCopernicus

Most of these issues show intriguing parallelisms to the front matter and the cosmological sections of Copernicus’s De revolutionibus,Book I. Most generally, the common outlook between Capuano and Copernicus is obvious. Like Regiomontanus, these two contem poraries see astronomy as a discipline at the apex of the sciences and one with physical consequences. They do not hesitate to use and to resolve, for their own purposes, arguments in natural philosophy. In addition, they both understand astronomy as causal.44 I now turn to some dialectical parallels between Capuano and Copernicus.

At one level, my suggestion that Copernicus appears to be answering Capuano is trivial. Since Copernicus argues against the set of all defenders of a central, stationary Earth, he is implicitly arguing against every member of the set, hence against Capuano.

As I hope to show, however, the issues that Capuano brings up inthis one treatise are sufficiently unusual, specific, and numerous to cast doubt on the hypothesis that the similarity is coincidental.  In De revolutionibus, I, after summarizing the main arguments for the centrality of the Earth and against its daily rotation (chap 44) Copernicus opens the manuscript of Book I with a reference to the “studies that deal with the godlike circular motions of the world” and lists among the topics in it

“the causes of the other phenomena of the heaven” (This passage was omitted in the 1543 edition); The Manuscript of Copernicus’ On the Revolutions: Facsimile, Complete ter 7), Copernicus in chapter 8 specifically takes on the arguments against the motion of the Earth. Instead of dealing piecemeal with the natural or unnatural character of such a rotation, he steps back to make a meta-point: if the Earth rotates, its motion is natural. Naturalness of motion will characterize whichever body is moving, whether the primum mobile or the Earth. Recall that one of Capua

no’s arguments for keeping the Earth stationary was that, if it moved, “there is no specifying that by which the Earth can move.” (33vb).Here, Copernicus’s appeal to its natural motion sounds like a direct answer to Capuano. In short, there is no independent criterion of natural motion, only a choice of options: either the heavens stand still and the Earth rotates, or the heavens rotate and the Earthstands still. In either case, the motion of the moving body and the immobility of the stationary one are natural; the question at hand is the determination of which body is in motion. In the process, Copernicus alludes to his own apocalyptic scenario if the heavensmove by raptus.45 Capuano had already rehearsed the arguments for the greater nobility of rest for the heavens and the greater ease of motion for the smaller body (the Earth), only to refute them. Copernicus adopted them.

Still in Chapter 8, Copernicus discusses the motion of comets (6r), and air. This passage caught the attention of Jamil Ragep, whowas puzzled by its apparent uniqueness in the Latin tradition.46 Significantly, Capuano had also discussed comets in the context of theraptus of the celestial spheres, not surprisingly perhaps, since the motion (or lack thereof) of the elements belongs to the problem of the motion (or lack thereof) of the Earth (30va). Copernicus uses raptus or its cognates three times in De revolutionibus I, 8

(6r-6v).
As we have seen, Capuano had argued that a sphere could move with mixed circular motion and elemental bodies could move with combined circular and straight motions. The availability of such arguments helps to explain Copernicus’s own appeal to mixed straight and circular motion (6r-v) and his rapid march through the tradi

tional natural philosophical problem of a rotating Earth in De revolutionibus I, 8. Although such arguments are scattered throughout fourteenth-century natural philosophy, we do not know precisely how they reached Copernicus. In Capuano’s revised commentary on the Sphere, they were not only readily available, but also put to work in a combined astronomical and physical context. Coperni cus put similar arguments to work for the elements, arguing that the apparent rectilinear rise and fall of the latter exhibit a compound of circular and rectilinear motion.47

But it is the matter of requiring more than one motion of the Earth that is most striking. In De revolutionibus I, 9, Copernicus’s argument resonates with the framework of Capuano’s discussion, which Copernicus has turned on its head. Having argued in De revolutionibus I, 8 that the mobility of the Earth is more probablethan its immobility, in the first sentence of Chapter 9, Copernicus asks, “whether several motions are appropriate for it” (7r).48 The immediate leap to the plural strikingly echoes Capuano’s argument rooted in De caelo, II, 14. After sketching his theory of gravity,49 Copernicus explores the consequences of making the Sun and Earth trade places and motions: “if the [yearly circuit] is transformed from solar into terrestrial, immobility being conceded to the Sun, the ris ings and settings of the zodiacal signs and the fixed stars, by which they become morning and evening stars, will appear in the same way.” On the force of this fundamental observational equivalence, Copernicus goes on to assert a stronger one:

“Also the stations, retrogressions, and progressions of the wandering stars will be seen to be not their own motion, but the Earth’s, which they transform into their appearances. Finally, the Sun itself will be thought to own the center of the universe….”50 These assertions are a direct denial of Capuano’s observational claim, which was probably rooted. in the objections of De caelo II, 14 and of Aquinas’s commentary on it, that the stars would exhibit “changes and turnings.”

If Copernicus had read the work, the incompatible premises in Capuano’s argument, generated by the juxtaposition of the simple motion of the fixed stars with the added assumption of “diurnal and zodiacal” motions, must have stood out when Copernicus tested. the consistency of his insight.

Strikingly, the passage in Capuano that immediately follows this discussion turns to the order of the planets, and discusses exten sively the place of Mercury and Venus in relation to the Sun: “Inthis question, it will be a matter first of the order of all the spheres;second, and more specifically, of the Sun, Venus, and Mercury.”5′

Precisely this problem, on Bernard Goldstein’s convincing interpre tation, motivated Copernicus’s move to heliocentrism by causing him to rethink the order of the planets-the subject of De revolutionibus I, ch. 1 0.52

Not least, Copernicus evidently agreed with Capuano that giving the Earth only diurnal and zodiacal motions could not save thephenomena. Accordingly, he spent the better part of De revolutionibus I, 1 1 offering two derivations of the third motion he ascribed to the Earth. Copernicus’s motion of “declination” keeps the Earth’saxis pointed in the same direction on an annual basis and also accounts for the precession of the equinoxes. Equally significant,immediately thereafter, the manuscript includes material omitted in the printed text, to the effect that Philolaus and Aristarchus probably saw the motions of the five planets as more consistent withthe mobility than the immobility of the earth “although they were not moved by the reason that Aristotle alleges and criticizes.”53 This
is a direct allusion to De caelo II, 14, the very passage that informsthe arguments of Aquinas and Capuano.

The significance of Capuano’s treatise lies less in the specific views he presents, many of which were scattered throughout late-medieval natural philosophy, than in his collection and linkage of them in a detailed commentary on the Sphere, the basic elementary text of the mathematical curriculum. In recasting Aristotle’s argument

against multiple motions of the Earth, Capuano called the two hypothetical motions “diurnal” and “zodiacal.” In so doing, he effec tively raised the possibility of the Earth’s being a planet-not sim ply a body rotating at the center of the universe, but a body with the traditional motions of the Sun. In Capuano’s commentary on the Sphere, written by a Paduan master whose path he may have crossed in Padua, Copernicus could conveniently find a range of recent and detailed arguments against the motion of the Earth. By1543, he had formulated arguments that look like answers tothem.

But was Copernicus answering Capuano? First, Copernicus verylikely knew about Capuano through the controversy with Alessandro Achillini. His studies in Bologna (1496-1500) overlapped with Achil lini’s tenure and publication of De orbibus (1498).54 A new piece of evidence increases the likelihood of his familiarity with Achilli ni’s work. De orbibus contains several mysterious citations from Averroes’s Epitome of the Almnagest, previously thought to be available only in Arabic and Hebrew.55 Equally intriguing, Copernicus cites this work, calling it Averroes in Ptolemaica paraphrasi, when discussing a possible transit of Mercury (De revolutionibus, 8v), the topic of one of Achillini’s quotations.56 Second, if Copernicus did not know about Capuano through Achillini in Bologna, he is likely to have heard about his commentaries (the commentary on Peuerbach competed with that of Brudzewo, who was probably Copernicus’steacher in Cracow). Ihird,

Copernicus and Capuano easily could have met: Copernicus’s years in Padua (1501-03) are bracketed by the years in which Capuano was publishing in the Veneto and presumably teaching his fellow canons there. Not least, Capuano’s Expositio of the Sphere was known in Copernicus’s circle. The Stockholm,Royal Library, copy of the 1518 Venice Giunta astronomical com pendium containing Capuano’s two works is inscribed to “loachimo Rhoetico.”57