Lecture 1 — What has gone before and what remains to be treated

403 We have already discussed the first heaven and its parts, the moving stars within it, the matter of which these are composed and their bodily constitution, and we have also shown that they are ungenerated and indestructible.

404 Now things that we call natural are either substances or functions and attributes of substances. As substances I class the simple bodies—fire, earth, and the other terms of the series—and all things composed of them; for example, the heaven as a whole and its parts, animals, again, and plants and their parts. By attributes and functions I mean the movements of these and of all other things in which they have power in themselves to cause movement, and also their alterations and reciprocal transformations. It is obvious, then, that the greater part of the inquiry into nature concerns bodies: for a natural substance is either a body or a thing which cannot come into existence without body and magnitude. This appears plainly from an analysis of the character of natural things, and equally from an inspection of the instances of inquiry into nature.

405 Since, then, we have spoken of the primary element, of its bodily constitution, and of its freedom from destruction and generation, it remains to speak of the other two.

406 In speaking of them we shall be obliged also to inquire into generation and destruction. For if there is generation anywhere, it must be in these elements and things composed of them. This is indeed the first question we have to ask: is generation a fact or not?

544. After determining the question of bodies that are moved circularly, the Philosopher here goes on to determine that of bodies that move in a straight line.

First he prefaces an introduction in which he explains his intention;

secondly, he pursues his intention, at earlier speculation was at variance (L. 2; 298b12).

Regarding the first he does two things:

first he establishes continuity with what has gone before by showing what has already been covered;

secondly, he states what remains to be discussed, at now things that we call natural (298a27; [546]).

545. He says therefore first (298a24) that in what has preceded he has gone through, i.e., treated briefly, the first heaven and the parts, namely, of it. Now we can understand by first heaven the whole universe, which is first in perfection, and take as its "parts" the bodies that are moved with circular and with straight motion. In this way it would seem that he is touching also what was determined in the first book. But this interpretation seems to be belied by his next phrase, and also the stars that are moved in it. Now, the stars are not properly said to be carried along in the whole universe, but in the heaven which is circularly moved. Hence it seems better to understand what he says of the first heaven to refer to the body which is moved circularly. But because he does not say simply heaven, but first heaven, this can be referred to the first sphere, which is that of the fixed stars; and parts to the right and left and the other different positions that he showed to exist in the heaven. But according to this interpretation there would not be a sufficient recalling, either of what was treated in the entire first book, or of all those things treated in the second, in which the spheres of the planets were also discussed. Consequently, it seems better to say that by "first heaven" is here understood the entire body which is circularly moved, and that it is called first in comparison to the lower bodies, in relation to which it is first in the order of position, and by reason of the eternity of its duration, and the power of its causality. The added expression, and the parts, would then refer to the various spheres which are parts of the whole celestial body. The stars that are moved in the whole heaven have also been treated, both the fixed stars and the planets Concerning them it has been stated of what they are composed: for it was shown that they are of the nature of the heavenly body. It has also been stated how they are according to nature, namely, that they are animated and spherical. Likewise it has been said that they are not subject to generation and decay. If the first book was a discussion of the whole universe, as we have said it was according to the opinion of Alexander, then this present review refers only to the second book. But if his [Aristotle's] intention in the first book also was to talk mainly about the heaven, as Simplicius avers, then this review extends even to the first book.

546. Then, at now things that we call natural (298a27), he shows what remains to be treated.

First, he shows in what the entire consideration of natural philosophy consists;

secondly, from this he concludes what remains to be said, after what has gone before, at since, then, we have spoken of the primary (298b6; [549]).

In regard to the first (298a27), he uses the following argument: All natural substances are bodies; but the whole consideration of natural science is about natural substances and their accidents; therefore the whole consideration of natural science is concerned with bodies.

547. First, therefore, he presents the minor, saying that among the things said to be according to nature, some are natural substances and some are the operations and passions of natural substances. In order to manifest this, he first explains which are the natural substances. Among these he first numbers simple bodies. And among these he gives as the first examples, fire and earth, and those others that are the elements of bodies together with these, as are air and water. And to the nature of these pertain the mixed [compound] bodies composed of them, such as stones and metals. Then he mentions another body beyond the elements, namely, the whole heaven and its parts. Lastly, he mentions animated composites, such as animals and plants and their parts. After this he manifests what the operations of these substances are. And he says that first, indeed, are the local motions of each of these bodies and also of the bodies of which these bodies are the cause, either the material cause, as are the elements, or the efficient, as is the heaven (and yet motion suits caused bodies according to the power of the simple bodies out of which they are caused). Then, he says that the activities and passions of the aforesaid substances are their alterations and transmutations into one another according to generation and corruption.

Secondly, he infers the conclusion and says that from the foregoing it is plain that most of natural history (i.e., the relating of the contents) deals with bodies. In saying most, he means "all," but he uses this mode of expression on account of his philosophic temperament. Or he says most on account of the fact that in natural science something is also said about the first mover and the intellective soul.

548. Thirdly, he presents the major, namely, that all natural substances are either bodies, or are generated with bodies and magnitudes, as are the natural forms, which are called "substances." And he says that this is evident in two ways:

First, from what has just been decided as being according to nature—all of which are either bodies or with bodies; and in Physics II it was determined that those things are according to nature which have within themselves their own principle of motion and rest; such things are bodies and only bodies, because only bodies are moved.

Secondly, he says that this is manifest by induction, if we consider one by one the things treated in natural science—for we find that all are bodies or with bodies. And it should be noted that he mentioned all this as a preface to book I.

549. Then, at since, then, we have spoken of the primary (298b6), he states what remains to be discussed.

First with regard to substances, saying that the heaven has been discussed, i.e., the first body among the elements, which he calls an "element" because it is a part of the world, according to Alexander; but according to Simplicius because it is a simple body. Concerning the heaven, its condition according to nature has been stated, namely, that it is animated and spherical, and also that it is indestructible and ungenerated. Hence the task which remains is to speak of the other two bodies. For it was shown in the first book that there are three bodies: one, namely, which is in motion around the center—which has already been treated; another, which is moved away from the center; and a third which is moved toward the center. These [last] two still remain to be treated—for the earth was discussed not with respect to its nature, but in its relation to the heaven.

550. Secondly, at in speaking of them we shall be obliged (298b8) he shows what remains to be said as to activities and passions [properties]. And he says that along with these two it remains to investigate generation and corruption, because either generation is nothing and has no connection with the nature of the entire universe, or it is found only in those elements that are moved with a straight motion and in bodies composed of them. But there was no place for this consideration so long as indestructible bodies were being considered. But this consideration must be taken up first, because it contributes a great deal to the consideration of the nature of bodies.