Dist. 14, Part 2, Art. 1, Q. 2
by St. Bonaventure
Source text: Public Domain Mark 1.0. English translation/apparatus/encoding: CC BY-NC 4.0, Wroot Press.
https://bonaventure.wrootpress.com/browse/2/d/14/q/bon-sent-II-d14-p2-a1-q2
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### Question II. *Whether the luminaries are moved in their own orbs by their own motions.*

Secondly it is asked whether the luminaries are moved in their orbs by their own motions. And that they are so, seems [the case].

*To the opposed view.*
1. For birds, which are for the adornment of the air, are moved in it by their own motion, and fishes in the waters: therefore by parallel reasoning the luminaries also in the heavens.

2. Likewise, the motion of the orbs is not posited except on account of the motion of the luminaries: for, the body being set aside, of themselves they have power to influence equally, whether they be moved or stand still; but nature does not do through many what it can do through fewer, nor does it do with greater difficulty what it can do with less: if therefore the motion of the star does the same as the motion of the whole orb does, it seems that it accords with nature to posit that the stars are moved by their own motions.

3. Likewise, if the luminaries are moved by the motion of their orbs, since they are moved by disparate motions and as if contrary to the starry heaven, then it seems that there would be there meeting and retardation, since that in which they are moved is one continuous body.

4. Likewise, we manifestly see by sight, that in the planets there are elevations and depressions, progressions and retrogradations; but this could not be, unless they had to be moved by their own motions: therefore etc.

*The foundations.*
**On the contrary:** 1. If the planets are moved by their own motions, then either two bodies will be in the same place, or it is necessary that the way by which the planet passes be empty, or it is necessary that the body of the heaven be rarefied and condensed, and so corrupted: but any of these is manifestly impossible: therefore etc.

2. Likewise, «nature does not fail in necessaries», especially with respect to those things that are nobler in itself: therefore if for those things which are moved by their own motion, it provided instruments, namely feet and wings or pinions, it seems that it ought to have given these to the celestial bodies; but they do not have them, as is plain to sense: therefore either nature fails in them, or they are not moved by their own motions.

3. Likewise, the stars in the eighth sphere are not moved except by the motion of that sphere: therefore if each planet is so placed in its orb, just as the stars in the eighth sphere, it seems that no luminary has [the power] to be moved by its own motion.

4. Likewise, if any luminaries were to be moved by their own motion to make progression or retrogradation, it would be impossible that the motion of the heaven be uniform: if therefore the motion is uniform and perpetual, it seems that there is nothing to it that the planets are moved by their own motions and sometimes retrocede, sometimes progress.

> **Conclusion.** The luminaries of heaven, more probably, are not moved by their own motions, but to the motion of the orbs in which they themselves are set.

**I respond:** It must be said that on this question there is controversy between the natural philosophers and the mathematicians.

*Opinion of the mathematicians.* For the mathematicians, considering above all the appearances, that they might save them together with the perpetuity and uniformity of motion, posited eccentrics and epicycles, and that the planets are moved by their own motions in the epicycles; and according to this, the uniformity of motion being preserved, sometimes it happens that the planet is depressed, sometimes elevated according to the motion of the planet itself in the epicycle, and of the epicycle in the eccentric, and of the eccentric about its own center, which is outside the center of the world. — But to the objection of the natural philosophers concerning the continuity of that body, they respond in various ways, saying that it is not unfitting if that body is split by the motion of the planet, since it is of fiery nature. Others say that that body is not split, and the planets pass through; for the body of light can be together with another body.

*Opinion of the Philosopher and conclusion.* But the position of the natural philosophers is, as of Aristotle and the Commentator, that the planets are not moved except by the motion of their orbs, just as a nail fixed in a wheel is moved by the motion of the wheel, not by its own; and they posit this on account of the incorruptibility of that body, on account of which it cannot be split nor afford passage to another body. They posit also that the center of the higher and lower orbs is the same, namely the center of the world, on account of the perfect roundness of those orbs themselves, which are moved circularly, so that one does not enter under the other. They posit also together with this a greater and lesser velocity in the orbs; and from this [that they] have now retrogradations, now progressions, because, when one body much precedes another by its velocity, the other seems to retrocede. And all these things seem very consonant to reason.

*Judgment about these.* And therefore, although the position of the mathematicians according to the *judgment of the senses* seems to be truer, because proceeding and judging in that way they are not deceived concerning the motions of the higher bodies; according to *the thing* however it need not be truer, because the false is frequently a way of finding the true; but the natural philosopher seems to proceed and posit more reasonably. — Therefore, if we should wish to sustain that position, it can be replied to those things which are objected on the opposite side.

*Solution of the opposed [arguments].*
1. To that, then, which is objected, that birds in the air and fishes in the waters are moved by their own motions; it must be said that it is not similar, because both air and water are bodies which can be rarefied and condensed. And besides, these elements are not so constituted by nature to be moved, like the bodies which pertain to their adornment, that by their motion [those bodies] can be sufficiently transmuted locally, according to what the beauty of the universe demands. Besides, to animals themselves progressive motion belongs on account of their indigence, and which is for attaining some delectable thing; and this neither can nor ought to belong to the luminaries of heaven.

2. To that which is objected, that the motion of the orbs is on account of the motion of the luminaries; it must be said that it is true; nevertheless from this it does not follow that the luminaries alone ought to be moved. For the integrity of the fifth body is not so preserved, if the stars are moved by their own motions, as if they are moved in their orbs, because there through such motion of celestial bodies there is no change from place to place according to the totality of the mobile, but about a place, nor any division of any body; and the whole perfection and incorruptibility of heaven required this.

3. To that which is objected, that, if they are moved by the motion of the orbs, it seems that there is retardation and meeting; it must be said that there is no meeting, except when bodies in motion meet one another directly along the same line. But here it is not so, because the lower orbs are under the higher; therefore their motion is not repugnant to them nor even retards [them], on account of the very great obedience of the mobile to the mover.

4. To that which is objected concerning those retrogradations and progressions, it must be said, as has been touched on, that although they seem to come about to sense, this is only on account of the greater and lesser velocity of the orbs themselves, which if anyone knew well how to explain, by this single way he could save that for the saving of which the mathematicians posit the multitude of circles and centers: but this pertains to another science.

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