Lecture 13 — From their shape the stars shown, not to move themselves. No sense power in the heavenly, bodies

303 There is, further, the absurdity that nature has bestowed upon them no organ appropriate to such movement. For nature leaves nothing to chance, and would not, while caring for animals, overlook things so precious. Indeed, nature seems deliberately to have stripped them of everything which makes selforiginated progression possible, and to have removed them as far as possible from things which have organs of movement. This is just why it seems proper that the whole heaven and every star should be spherical. For while of all shapes the sphere is the most convenient for movement in one place, making possible, as it does, the swiftest and most selfcontained motion, for forward movement it is the most unsuitable, least of all resembling shapes which are self-moved, in that it has no dependent or projecting part, as a rectilinear figure has, and is in fact as far as possible removed in shape from ambulatory bodies. Since, therefore, the heavens have to move in one lace, and the stars are not required to move themselves forward, it is natural that both should be spherical—a shape which best suits the movement of the one and the immobility of the other.

411. Having presented two arguments to show that the stellar bodies are not moved with a motion of their own but are carried along by the motion of their circles or spheres, the Philosopher now proves the same thing with a third argument (290a29), which is based on the shape of the stars. And he says that if the stars were moved with a forward motion, as though walking through their circles, it would seem unreasonable that nature should not equip them with instruments suitable for local motion. For nature does not produce its effects haphazardly especially when it comes to its more noble products. Consequently, it is not unreasonable to suppose that nature would have care for terrestrial animals by equipping them with organs suitable for progressive motion and would neglect bodies as precious as the stars and not equip them with organs suitable for progressive motion. Rather it seems that nature deliberately did not intend the stars to be moved on their own, from the fact that it deprived them of all instruments by which they might move of themselves with progressive movement, and furthermore, because the stars are most removed from the shape of animals having instruments suitable to progressive motion. For animals of this sort, the more perfect they are, the greater variety do they exhibit in their parts—but the stars have everywhere the greatest degree of uniformity, since they are spherical in shape.

412. On this account it seems reasonable for the entire heaven, and for each star, to be spherical. For a spherical shape seems uniquely suitable to circular motion, i.e., a motion in which a spherical body is moved in itself, i.e., not changing its place as a whole except as to notion, but only as to its parts, as is proved in Physics VI. The fact that a body circularly moved is spherical allows it to be moved with the greatest speed, not only because a circular line is the smallest of all the figures that can contain an equal area but also because rectilinear bodies do not have a uniform motion in every part, since they are more fixed wherever they have a flat surface than where they have corners. Hence, since a sphere is nowhere flat but everywhere constitutes a point, i.e., a corner, it is plain that a spherical body moves swiftest with a circular motion. Likewise, it will most perfectly retain its own place, since no part of it ever begins to be except where another was, whereas this does not happen with rectilinear bodies, whose corners jut out further than their surfaces. However, a spherical shape is least suited for forward motion. Sphericity has nothing in common with the bodies of animals that are capable of self-movement. For there are not depressions or eminences in a sphere as there are in a rectilinear body. But sphericity is most unlike the shape of the bodies of animals which move forward by a certain raising and lowering, for which reason the members of animals are flexible at their joints in order to be suitable for progressive movements.

Since, therefore, it was necessary for the whole heaven, i.e., the sphere thereof, to be moved with circular motion, whereas the stars were not to be moved with a forward motion, it was reasonable for each to be made spherical, namely, both the sphere and the star. For the heaven being spherical makes it suitable for circular motion, and the stars' being spherical makes them unsuited for progressive motion. Consequently, the latter are not moved within the circles, but, while remaining stationary in themselves, are carried along by the motion of the circles.

413. Now, a difficulty can arise here: namely, since the bodies of the spheres are not visible, being transparent, and it could be said that the stars are moved, as it were, in air, why did Aristotle omit to make inquiry on this point?

But it should be said that it is abundantly clear from Aristotle's teachings that in the heaven are not only distinct stellar bodies but also distinct bodily spheres.

First, from the fact that he shows the stars are not being moved on their own by the motion which appears in them.

Secondly, it is clear from an argument he previously gave, namely, that there would be no reason why a star which traverses a greater circle should be moved more swiftly, whereas there is a reason if a motion of the circles is assumed, since it is reasonable for a greater circle by its own motion to be moved more swiftly.

Thirdly, because Aristotle in the beginning of this book proved that there is a body which is moved circularly, while the movement of a star, if it were moved on its own, without its orb, would be progressive and not circular, because it would not be moved while remaining in the same place.

Fourthly, because that space in which the stars would be moved cannot be void, since it is impossible for a void to exist in nature, as was proved in Physics IV. But if it were filled with some other body that had nothing in common with the nature of the stars, for example, fire or air, this would be clearly unacceptable for two reasons. First, because it is not fitting for one and the same place to act as a place for generable-corruptible bodies such as fire and air, and for uncorruptible bodies, namely, the stars, since diverse bodies have places that are diverse, each being suited to the natures involved. Secondly, because it is not reasonable that the lower bodies be continuous and the heavenly bodies mutually discontinuous. What remains therefore is that the entire space in which the stars are seen to be moved is filled with a heavenly body which pertains to the very substance of the spheres.

Fifthly, it is clear from the fact that the sun and moon are moved upon circles that mutually intersect. This is plain from the fact that the moon is now north and now south of the circle in which the sun is moved. But it is evident that the intersections of two circles which are called "nodes," or "head and tail," do not occur always in the same points, since they cannot happen unless the moon is in conjunction or in opposition to the sun with respect to one of these nodular points. But if this variation were due solely to the motion of the moon, it would follow that the moon would not be moved circularly but spirally, which is contrary to the nature of the heavenly bodies. Therefore, it is plain that the circle of the moon has a motion of its own. For the same reason, so do the circle of the sun and those of the other stars.

414. Now it should be kept in mind that when Aristotle states it is not reasonable that nature would be solicitous for the animals and neglect so precious bodies, he is not calling stars animals. Because, as Alexander says, it is sensitivity that makes up the animal nature; but in the heavenly bodies, if they are animate, there is not the sensitive power of the souls nor likewise the nutritive. Wherefore, it is only in an equivocal sense that they are called animals, namely, because they have an intellective soul.

However, in his commentary, Simplicius endeavors to refute this on the ground that if anything honorable is attributed to terrestrial bodies, then with more reason to heavenly bodies. But since sensitivity pertains to the excellence of a body, there seems to be much more reason for heavenly bodies to possess it than terrestrial bodies.

Morover, since heavenly bodies touch one another, it seems unfitting that they should not sense one another. Therefore, he concedes the existence of three senses in heavenly bodies, namely, sight, hearing and touch, but excludes from them the other two more material senses, namely, smell and taste.

415. Let us see, therefore, how much of this is in accord with the judgment of Aristotle, who seems to feel that no part of the soul but the intellective is found in the heavenly bodies. For he says in Metaphysics XII that the first mover moves the heaven as an object of desire, not indeed by the desire of sense, but by the desire of intellect. And in On the Soul II he says: all corruptible things that possess reason possess all the rest—as though this were not the case in incorruptible bodies, in which he believed intellect or reason to exist without the other powers of the soul.

But a statement of his in On the Soul III raises a difficulty. He says, a body cannot have a soul and a discerning intellect without possessing sensation, if it is not stationary, i.e., [missing text] i.e., if it is produced by generation, i.e., if it is generated and corruptible, as is evident in men and other animals of this sort. He continues: nor yet even if it were not produced by generation—by which he seems to signify that, not even if a body is ungenerated and incorruptible, as are the heavenly bodies, would it have intellect without sensation. In proof of this he adds: why should it not have?—i.e., not have sensation, seeing that it has intellect. Because it were better so for the body or for the soul, which is as though saying that the lack of sensation is either for the good of the body or for the good of the soul. Then he goes on: but clearly it would not be better for either—for the absence of sensation will not enable the one [the soul] to think better or the other [the body] to exist better [i.e., more durably]. Then he concludes: therefore, no body which is not stationary has soul without sensation. From this he appears to feel that if heavenly bodies are animated with a rational and intellective soul, they also have sensation. But what he immediately adds goes counter to this interpretation: but if a body has sensation, it must be either simple or mixed. And simple it cannot be; for then it could not have touch, which is indispensable. Since, therefore, the heavenly bodies are simple, they cannot possess sensation.

416. Hence the above-quoted words of Aristotle are explained by Themistius and Averroes in their commentaries in the sense that the expression, not even if it were not produced by generation, means not even that which is incorruptible, namely, a heavenly body, has sensation. And why does it not have sensation?—as though saying that this is the reason why it does not, namely, because it were better so either for the soul or for the body, i.e., if a heavenly body had sensation, it would possess it either for the good of the soul or for the good of the body. But clearly it is not better for either, for the one [namely, the soul of the heavenly body], will not understand any better [for its intellect is not the kind that receives from the senses as the human intellect does; rather such an intellect understands after the manner of a separated substance, to which it is immediately continuous in the hierarchy of things]; nor will the other [namely, the body] exist any better. because of this, i.e., it will not be kept in existence through sensation as occurs with the bodies of earthly animals, which are preserved from corruptive things through sense, as is plain from what he had already said [in On the Soul].

Now this explanation seems to be more fitting than the other, so far as the efficacy of the argument is concerned. For in order to show that something is not without purpose, it is more necessary to show for what purpose something exists than to show for what purpose something does not exist. Hence, in order for the heaven not to possess sensation, it is enough to show that no advantage would come to it from sensation (and these are the lines according to which the second explanation proceeds). Accordingly, it is not necessary to show that it is better for it not to have sensation (which is the way the first explanation proceeds). For if no advantage would accrue to the heaven from sensation, that is reason enough for not having sensation. But the conclusion which he draws appears not to fit this understanding, but rather the previous one. For he subsequently concludes, therefore no body that is not stationary has soul without sensation. However, it could be said that this conclusion is connected not with what immediately preceded it, but with what he had said above about generable bodies.

Yet, because this interpretation seems somewhat extorted, it seems better to say that the phrase, not even what is not produced by generation, should be continued with the preceding statement, so that its meaning would be just as a body which is produced by generation does not have an intellective soul without sensation, so also a body that is not produced by generation. But by the phrase, "a body that is not produced by generation," is not meant here the heaven—which is evident from the fact that the heaven remains in the same place as to its entirety, whereas he is here speaking of a body that is not stationary. Therefore, Aristotle seems to be speaking here of certain animated bodies which the Platonists called "demons," and described as being animals possessed of an airy body and eternal in time, as the Platonist Apuleius says in his book, On the God of Socrates. They posited such bodies as moving with progressive motion and not stationary in the same place.

417. But anyone who considers the position of the heavenly bodies among natural bodies will see that it does not befit the former to have no sensitive potency.

First, because these bodies are not passive, but active. Hence, it is not suitable for their souls, if the bodies are animate, to have sensitive potencies, which are passive.

Secondly, because such bodies, being spherical, are uniform, whereas a body possessing sensitivity must have a variety of organs. For, since sense is a power knowing individual things, a body must have diverse sensitive powers if it is to sense perfectly, by which it may know the different genera of sensible things, different organs being adapted for different senses. Hence, the uniformity of the spherical body conflicts with the disposition of the sensitive soul.

Thirdly, because the heavenly bodies are as though the universal causes of lower effects. Consequently, sensible effects pre-exist in the heavenly bodies not according to a singular, but according to a universal, notion, as being in universal causes. With much more reason, then, do the notions of sensible things exist in the souls of heavenly bodies (if they are animate), not according to a singular notion, which is proper to sense, but according to a universal notion, which belongs to intellect.

418. The heavenly bodies, therefore, if they are animated, have intellect without sense. But just as the intellect of separated substances knows not only universals but also particulars (for they have by one knowing power what we have by several, so, too, the souls of heavenly bodies with their intellect know not only universals but particulars as well. For it is thus in all things, that the perfections which are attributed to the lower through many, a higher thing possesses through one—just as imagination is one power capable of knowing all sensible things, which things sense, however, perceives through different powers.

This also excludes an objection presented by Avicenna who, in his Metaphysics, shows that the soul of a heavenly body must have an imagination through which it may perceive the individual positions it assumes in the heaven by its motion, just as our practical intellect does not act according to a universal apprehension without a particular, as is said in On the Soul III. For, according to what has been said, the substance which moves the heaven—whether it be a separated substance or a soul—can perceive individual positions through the intellect without sense, as has been said.

419. The objection of Simplicius, that sensing pertains to the nobility of a lower body, and hence is even more appropriate for a heavenly body, is answered in two ways.

First of all, because, since the soul is not for the sake of the body but vice versa, we should not, when considering the potencies of the soul, primarily consider what pertains to the nobility of the body, but what pertains to the notion of soul.

Secondly, because that which lower bodies possess, namely, the ability to know sensible things, in an inferior way, that is, through sensation, is possessed by heavenly bodies in a higher way, namely, through an intellective soul united to them.