Commentary Aristotle Physics
Lecture 2
The ancient philosophers’ opinions about the principles of nature and of beings
The principles in question must be either one or more than one. If there is one, it must be either motionless, as Parmenides and Melissus assert, or in motion, as the physicists hold—some declaring air to be the first principle, others water. If there are more than one, then either a finite or an infinite plurality. If they are finite (but more than one), then either two or three or four or some other number. If they are infinite, then either (as Democritus believed) one in kind but differing in shape or form, or different in kind and even contrary.
A similar inquiry is made by those who inquire into the number of existents. For they inquire whether the ultimate constituents of existing things are one or many, and if many, whether a finite or an infinite plurality. So they, too, are inquiring whether the principle or element is one or many.
Now, to investigate whether being is one and motionless does not belong to natural science. For just as the geometer has nothing more to say to one who denies the principles of his science—this being a question for a different science or common to all—so a man investigating principles cannot argue with one who denies their existence.
For if being is just one, and one in the way mentioned, there is no longer a principle, since a principle must be the principle of some thing or things.
To inquire, therefore, whether being is one in this sense would be like arguing against any other position maintained for the sake of argument, such as the Heraclitean thesis or such a thesis as that being is one man—or like refuting a merely contentious argument. This applies to the arguments both of Melissus and of Parmenides: they have accepted what is false and they are not syllogizing. Or rather, the argument of Melissus is much worse and offers no difficulty at all: accept one ridiculous proposition, and the rest follow—a simple enough proceeding.
We physicists, on the other hand, must take for granted that the things that exist by nature are—either all or some of them—in motion. This is indeed made plain by induction.
Moreover, no one is bound to solve every kind of difficulty that may be raised, but only as many as are drawn falsely from the principles of the science. It is not our business to refute those that do not arise in this way; just as it is the duty of the geometer to refute the squaring of the circle by means of segments, but it is not his duty to refute Antiphon’s proof.
At the same time, the holders of the theory of which we are speaking do incidentally raise physical questions, though nature is not their subject, so it will perhaps be as well to spend a few words on them, especially as the inquiry is not without philosophical interest.
12. Having completed the preface, in which it was shown that natural science ought to begin with the more universal principles, he here begins, according to the order already stated, to pursue those matters that pertain to natural science.
This discussion is divided into two parts.
In the first part, he treats the universal principles of natural science.
In the second part, he treats mobile being in common, which is what he intends to treat in the Physics. This is taken up in book 3, at “nature has been defined” (200b12; [275]).
The first part is divided into two parts.
First, he treats the principles of the subject of this science, that is, the principles of mobile being as such;
second, he treats the principles of the doctrine. This he does in book 2, at “of things that exist” (192b8; [141]).
The first part is divided into two parts.
First, he considers the opinions others have had concerning the common principles of mobile being.
Second, he seeks the truth concerning them, at “all thinkers, then, agree” (188a19; [75]).
Concerning the first part, he makes three points.
First, he sets forth the different opinions of the ancient philosophers concerning the common principles of nature.
Second, at “now, to investigate” (184b25; [15]), he shows that it does not pertain to natural science to pursue some of these opinions.
Third, at “the most pertinent question” (185a20; [21]), he considers these opinions, showing their falsity.
Concerning the first part, he makes two points.
First, he sets forth the different opinions of the philosophers concerning the principles of nature.
Second, at “a similar inquiry is made” (184b21; [14]), he shows that this same diversity exists with reference to the opinions of the philosophers concerning beings.
13. He says, therefore, first of all (184b15), that it is necessary that there be either one principle of nature or many. And each position has claimed the opinions of the philosophers.
Some of them, indeed, held that there is one principle; others held that there are many. And, of those who held that there is one principle, some held that it was immobile, as did Parmenides and Melissus, whose opinions he will examine below. Some, however, held that it was mobile, as did the natural philosophers.
Of these, some held that air was the principle of all natural things, as did Diogenes, but others held that it was water, such as Thales, others that it was fire, such as Heraclitus, and still others some mean between air and water, such as vapor.
But none of those who held that there was only one principle said that it was earth, because of its density. For they held that principles of this sort were mobile, because they said that other things come to be through the rarefaction and condensation of certain of these principles.
Of those who held the principles to be many, some held them to be finite, while others held them to be infinite.
Of those who held that they were finite (although more than one), some held that there were two—fire and earth—as he will say of Parmenides below. Others held that there were three: fire, air, and water (for they thought earth to be composed in some way, because of its density). Others, however, held that there were four, as Empedocles did, or even some other number (for even Empedocles himself posited two other principles, friendship and strife, along with the four elements).
Those who held that there was an infinite plurality of principles had a diversity of opinions. Democritus held that indivisible bodies called “atoms” are the principles of all things, and he held that bodies of this sort were all of one genus according to nature, but that they differed according to figure and form, and that they not only differed but even had contrariety among themselves. For he held three contrarieties:
one according to figure, which is between the curved and the straight;
another according to order, which is the prior and the posterior;
and another according to position, namely, before and behind, above and below, or to the right and to the left.
And so he held that, from these bodies existing of one nature, different things come to be according to the diversity of the figure, position, and order of the atoms.
In this opinion, then, he gives us some basis for understanding the opposing opinion, that of Anaxagoras, who held that the principles were infinite but not of one genus according to nature. For he held that the principles of nature were the infinite, smallest parts of flesh, bone, and other such things, as will be made clear below.
It must be noted, however, that he did not divide these many principles into mobile and immobile. For none of those who held that the first principles were many held that they were immobile. For since all place contrariety in the principles, and since it is natural for contraries to change, immobility could not stand with a plurality of principles.
14. Second, at “a similar inquiry is made” (184b21), he shows that there is the same diversity of opinions concerning beings. He says that, in like manner, the physicists, when inquiring about those things that are—that is, about beings—wondered how many there are, namely, whether there is one or many, and if many, whether finite or infinite.
And the reason for this is that the ancient physicists did not know any cause but the material cause (although they touched lightly upon the other causes). Rather, they held that the natural forms were accidents, as the forms of artificial things are. Since, therefore, the whole substance of artificial things is their matter, so it followed, according to them, that the whole substance of natural things would be their matter.
Hence, those who held one principle only—for example, air—thought that other beings were air according to their substance. And the same is true of the other opinions. Hence Aristotle says that the physicists seek the ultimate constituents of existing things; that is, in inquiring about principles, they sought the material causes from which beings are said to be. Thus it is clear that, when they inquire whether beings are one or many, their inquiry concerns the material principles that are called elements.
15. Next, at “now, to investigate” (184b25), he shows that it does not pertain to natural science to disprove some of these opinions.
And concerning this, he makes two points.
First, he shows that it does not pertain to natural science to disprove the opinion of Parmenides and Melissus;
second, at “at the same time, the holders of the theory” (185a17; [19]), he gives a reason why it is useful to the present work to disprove this opinion.
Concerning the first part, he makes two points.
First, he shows that it does not pertain to natural science to disprove the opinion already given.
Second, at “or like refuting” (185a7; [17]), he shows that it does not pertain to natural science to resolve the arguments that are brought forth to prove this opinion.
He establishes his first point with two arguments, the second of which begins at “to inquire, therefore” (185a5; [16]).
He says, therefore, that it does not pertain to natural science to undertake a thorough consideration of the opinion whether being is one and immobile. For it has already been shown that, according to the intention of the ancient philosophers, there is no difference whether we hold one immobile principle or one immobile being. And that it should not pertain to natural science to disprove this opinion he shows as follows. It does not pertain to geometry to bring forth reasons against an argument that destroys its principles. Rather, either this pertains to some other particular science (if, indeed, geometry is inferior to some particular science as music is inferior to arithmetic, to which it pertains to dispute against any position denying the principles of music) or it pertains to a common science, such as logic or metaphysics.
But the position just given destroys the principles of nature. For if there is only one being, and one in the way mentioned, namely, immobile, such that others cannot come to be from it, then the very definition of a principle is taken away. For every principle is a principle either of some thing or of some things.
Therefore, if we posit a principle, multiplicity follows, because one is the principle and the other is that of which it is the principle. Therefore, whoever denies multiplicity also removes principles. Therefore, natural science ought not to argue against this position.
16. Next, at “to inquire, therefore” (185a5), he shows the same point with another argument. It is not required of any science that it bring forth arguments against manifestly false and untenable opinions. For it is stupid to worry about one who offers positions contrary to the opinions of the wise, as is said in Topics 1.11.
He says, therefore, that to undertake a thorough consideration of the question whether being is one (and hence immobile) is like arguing against any other untenable position. For example, it is like arguing against the position of Heraclitus, who said that all things are always moved and that nothing is true, or against the position of one who would say that the whole of being is one man—which position, indeed, would be altogether untenable. And indeed, whoever holds being to be only one immobile thing is forced to hold that the whole of being is some one thing. It is clear, therefore, that it does not belong to natural science to argue against this position.
17. Next, at “or like refuting” (185a7), he shows that it does not belong to natural science even to resolve the arguments of the previously mentioned philosophers.
And this is for two reasons, the second of which begins at “we physicists” (185a12; [18]).
First, he proves his position by pointing out that it is not incumbent upon any science to resolve sophistic arguments that have an obvious defect of form or matter. He says that to deal with untenable arguments is like refuting a merely contentious, that is, sophistic, argument. But each argument of both Melissus and Parmenides is sophistic, for they err in matter. Thus he says that they have accepted what is false; that is, they assume false propositions. They also err in form; thus he says that they are not syllogizing. But the position of Melissus is much worse, that is, more vain and foolish, and offers no difficulty, that is, does not give rise to any doubt. This will be shown below. Moreover, it is not inconsistent that, given one inconsistency, another should follow. Therefore, it can be concluded that it is not required of the philosopher of nature that he resolve the arguments of this man.
18. He sets forth the second argument for this at “we physicists” (185a12). The argument is as follows. In natural science, it is supposed that natural things are moved, either all or some of them. He says this because there is doubt whether some things are moved and how they are moved—for example, about the soul and the center of the earth, and the pole of heaven, and about natural forms and other such things.
But the fact that natural things are moved can be made clear from induction, for it is apparent to the sense that natural things are moved. It is as necessary that motion be supposed in natural science as it is necessary that nature be supposed. For motion is placed in the definition of nature, since nature is a principle of motion, as will be said below.
Having established this point—that motion is supposed in natural science—he proceeds further to prove his position as follows. Not all arguments must be resolved in any science, but only those that conclude something false from the principles of that science. Any arguments that do not reach their conclusions from the principles of the science, but from the contraries of these principles, are not resolved in that science.
He proves this by an example taken from geometry, saying that it pertains to geometry to resolve the problem of squaring (that is, the squaring of a circle) by means of segments of the circumference, because this method supposes nothing contrary to the principles of the science of geometry. For a certain man wished to find a square equal to a circle by dividing the circumference of the circle into many parts and placing straight lines in each part. And so, by finding some rectilinear figure equal to some of the figures that were contained by the dissections of the circumference and either many or all of the chords, he thought he had found a rectilinear figure equal to the whole circle, to which it was easy to find an equal square through the principles of geometry. And thus he thought that he was able to find a square equal to a circle.
But he did not argue well enough, for although these dissections used up the whole circumference of the circle, the figures contained by the dissections of the circumference and the straight lines did not encompass the whole circular surface.
But to resolve the square of Antiphon does not pertain to geometry, because he used principles contrary to those of geometry. For he described in a circle a certain rectilinear figure, such as a square, and divided in half the arcs by which the sides of the square were subtended. From the points of dissection, he led straight lines to all the angles of the square. Then there resulted in the circle a figure of eight angles that more closely approached equality with the circle than the square. Then he again divided in half the arcs by which the sides of the octagon were subtended, and thus, by leading straight lines from the points of dissection to the angles of this figure, there resulted a figure of sixteen angles that still further approached equality with the circle. Therefore, by always dividing the arcs and leading straight lines to the angles of the figure already existing, there will arise a figure very near to equality with the circle. He said, then, that it was impossible to proceed to infinity in the dissection of arcs. Therefore, it was necessary to arrive at some rectilinear figure equal to the circle to which some square could be equal. But, because he supposed that an arc is not always divisible in half, which is contrary to the principles of geometry, it does not pertain to geometry to resolve an argument of this sort.
Therefore, because the arguments of Parmenides and Melissus suppose being to be immobile, as will be shown below, and since this is contrary to the principles supposed in natural science, it follows that it does not pertain to the natural philosopher to resolve arguments of this sort.
19. Next, at “at the same time” (185a17), he states why he will argue against the aforementioned position. He says that, because the philosophers mentioned above did speak of natural things, even though they did not create questions (that is, in the sphere of natural science), it is useful for his present purpose to argue against opinions of this sort. For even though it does not pertain to natural science to argue against such positions, it does pertain to first philosophy.