Lecture 25 — Reason for earth's rest not from same relation to every part of the heaven

372 but there are some, Anaximander, for instance, among the ancients, who say that the earth keeps its place because of its indifference. Motion upward and downward and sideways were all, they thought, equally inappropriate to that which is set at the center and indifferently related to every extreme point; and to move in contrary directions at the same time was impossible: so it must needs remain still.

373 This view is ingenious but not true. The argument would prove that everything, whatever it be, which is put at the center, must stay there. Fire, then, will rest at the center: for the proof turns on no peculiar property of earth.

374 But this does not follow. The observed facts about earth are not only that it remains at the center, but also that it moves to the center. The place to which any fragment of earth moves must necessarily be the place to which the whole moves; and in the place to which a thing naturally moves, it will naturally rest. The reason then is not in the fact that the earth is indifferently related to every extreme point: for this would apply to any body, whereas movement to the center is peculiar to earth.

375 Again it is absurd to look for a reason why the earth remains at the center and not for a reason why fire remains at the extremity. If the extremity is the natural place of fire, clearly earth must also have a natural place. But suppose that the center is not its place, and that the reason of its remaining there is this necessity of indifference—on the analogy of the hair which, it is said, however great the tension, will not break under it, if it be evenly distributed, or of the men who, though exceedingly hungry and thirsty, and both equally, yet being equidistant from food and drink, is therefore bound to stay where he is—even so, it still remains to explain why fire stays at the extremities.

376 It is strange, too, to ask about things staying still but not about their motion,—why, I mean, one thing, if nothing stops it, moves up, and another thing to the center.

377 Again, their statements are not true. It happens, indeed, to be the case that a thing to which movement this way and that is equally inappropriate is obliged to remain at the center. But so far as their argument goes, instead of remaining there, it will move, only not as a mass but in fragments. For the argument applies equally to fire. Fire, if set at the center, should stay there, like earth, since it will be indifferently related to every point on the extremity. Nevertheless it will move, as in fact it always does move when nothing stops it, away from the center to the extremity. It will not, however, move in a mass to a single point on the circumference—the only possible result on the lines of the indifference theory—but rather each corresponding portion of fire to the corresponding part of the extremity, each fourth part, for instance, to a fourth part of the circumference. For since no body is a point, it will have parts. The expansion, when the body increased the place occupied, would be on the same principle as the contraction, in which the place was diminished. Thus, for all the indifference theory shows to the contrary, earth also would have moved in this manner away from the center, unless the center had been its natural place.

We have now outlined the views held as to the shape, position, and rest or movement of the earth.

514. Having presented the fourth solution according to which the explanation of the earth's rest was taken from the violence of the heaven's gyration, the Philosopher here presents the fifth solution in which the explanation of the earth's rest is based on the fact of a similar relation of the heaven to the earth from all directions.

First, he presents this explanation;

secondly, he disproves it, at this view is ingenious (295b16; [515]).

He says therefore first that some have said that the earth rests in the middle because of likeness, i.e., on account of its being similarly related to every part of the heaven. Among the ancients, Anaximander held this opinion. By this he gives us to understand that some of his contemporaries believed this. For Plato is said to have posited this; yet Aristotle does not attribute it to him because above he had attributed to him the opinion that the earth was moved in the middle about the axis of the world. Now the reason why they said that the earth stays put on account of likeness, is that there is no reason why that which is placed in the middle should be moved upward or downward, or toward other reaches of the heaven, since it is related in the same way to the extremes in every direction. Now it is impossible for it to be moved simultaneously in contrary directions. Therefore it remains that it necessarily rests in the middle.

515. Then, at this view is ingenious (295b16), he disproves this explanation.

First, on the ground that the argument does not have necessity;

secondly, on the ground that it supposes something false, at again, their statements are not true (296a3; [519]).

He says therefore first (295b16) that the statements they make appear persuasive, but are not truly so. And this he proves with four arguments.

The first of these is that, if the above explanation were true, then everything placed in the middle would have to rest there (and thus it would follow that fires if it were put in the middle, would remain at rest, which is patently false), because the cause of rest assigned here, namely, being in the middle, is not taken to be peculiar to earth yet the effect, namely, to be at rest in the middle, is peculiar to earth.

516. The second argument is presented at but this does not follow (295b19), and he says that it is not necessary to say that the earth rests in the middle on account of likeness, since a more suitable cause is available. For earth seems not only to rest in the middle, but to be borne toward the middle, if not according to the whole, nevertheless according to its parts. Now there is the same explanation for the motion of the whole and for that of the part. For whithersoever a part of the earth is borne, there too the whole would be necessarily borne, should it be outside its proper place. But wherever it is borne according to its nature, there it also rests according to its nature. Accordingly, it is plain that the earth rests in the middle on account of its very nature and not because it is related in a "liken way" to the extremes, since to be put in the middle can be common to all things—but to be naturally borne to the middle is peculiar to earth.

517. He gives his third argument at again it is absurd (295b25), which also shows the insufficiency of this explanation. And he says it is inappropriate to investigate why the earth rests in the middle and not investigate why fire rests in the extreme confine. For if fire rests there because the extreme place naturally suits it, then for the same reason it should be said that earth too has a natural place in which to rest. And if the middle is not the place where earth naturally rests, but it remains in the middle on account of the necessity of likeness, then they must investigate why fire remains in the extremes.

And he gives examples of the earth's rest in the middle based on certain arguments of the sophists, who seemed to prove that a trichos, i.e., a hair, if vigorously stretched, would not break, because it would be stretched alike in every direction and there is no reason why it should break at one point rather than at another. But this argument is sophistical: first, because it is difficult for it to be stretched everywhere in the same way; secondly, because, even supposing this, it would break in the middle, because it is there that the violence exerted from both directions meets. He gives another example, namely, of a person subject to an equal degree of hunger and thirst and having food and drink at an equal distance. The sophists conclude that such a person would remain where he is, and be moved to neither. But this does not follow: first of all, because thirst is stronger than hunger; secondly, because, if two meals or two drinks were equally desirable, he would run to whichever one he should happen to run to.

518. He presents his fourth argument at it is strange, too (296a1), which also shows the insufficiency of the aforesaid. And he says that it was strange for them to inquire into the reason why bodies rest and not inquire into the reason for their motion, namely, as to why one body is moved upward and another downward when no obstacle detains them. For nature is the principle of motion and rest in that in which it is, as is said in Physics II.

519. Then, at again, their statements are not true (296a3), he disproves the aforesaid explanation on the ground that it assumes something that is false. And he says that what is said in the aforesaid explanation is not true per se and universally. For it is per accidens true that everything, i.e., a whole, must remain in the middle if there is no greater reason for it to be moved here than there. But if it should have an inclination to be moved in some direction, then, because of the fact that it is in the middle, it will not rest of necessity, but it will be moved—yet not as a whole, but divided into parts, as is evident with fire. For if what they say is true, then, if fire were put in the middle of the world, it would have to remain there, as the earth does, on the ground that it would be similarly related to every point that can be designated in the heaven; yet if fire were put in the middle, it would be moved to the extreme if nothing stopped it, as it is even now seen to be moved. But yet, not all is moved to one point—and this alone was removed in the previous argument, namely, that the whole should be moved in one direction. But each portion of the fire will be moved to a part of the heaven suitable to it—for example, a fourth part of the fire to a fourth part of the container, i.e., the heaven; for a body is not an indivisible point. Just as parts of earth, if dispersed toward the confines of the heaven, would be condensed to come to a lesser place, namely, the middle, so also conversely, if fire were moved from the middle to the extreme, it would have, by rarefaction, to be moved from a small place to a larger place.

520. And thus ceases the objection upon which someone could gainsay the foregoing and declare that it is impossible for individual portions of fire to be borne to individual parts of the heaven on the ground that the extreme place exceeds the middle in quantity. For this is forestalled by the fact that through rarefaction the fin: would be extended to occupy a greater place. And from this he concludes that if the middle place were not natural to earth, then, on account of likeness, it would be moved in such a way from the middle to the extreme that each of its parts would be moved to individual parts of the extreme, as was said of fire.

Finally, he sums up and says that this is practically all that the ancient philosophers suspected about the shape and place of the earth and about its place and its motion or rest.