Commentary Aristotle Physics
61. Next, at “moreover, the fact that” (187a31), he mentions the second thing that Anaxagoras assumed. Anaxagoras said that contraries come to be from each other. For we see the cold come to be from the hot, and vice versa. And from this he concluded that, since nothing comes to be from nothing, one of the contraries preexists in the other. And this is true, of course, in respect to potency. For the cold is in the hot in potency, but not in act, as Anaxagoras thought. For he was not aware of being in potency, which is a mean between pure non-being and being in act.
62. Next, where he says, the one, they reasoned (187a32), he sets forth the deductive order of the argument. Anaxagoras proceeded as follows. If something comes into being, it is necessary that it should come to be either from being or from non-being.
But he excluded one of these alternatives—namely, that something should come to be from non-being. He did this because of the common opinion of the philosophers mentioned above.
From this, he concluded that the remaining alternative was correct, namely, that a thing comes to be from being. For example, if air comes to be from water, then air preexisted. For it cannot be said that air comes to be from water unless air preexisted in water.
Hence he wished to say that everything that comes to be from something preexisted in that from which it comes to be.
But, because this seemed to be contrary to what appears to the senses (for it is not apparent to the senses that that which is generated from something preexists in it), he forestalled this objection by holding that that which comes to be from something preexists in it as certain most minute parts that are not sensible to us because of their smallness. For example, if air comes to be from water, certain minute parts of air are in the water, but not in that quantity in which it is generated. And so he said that, by the gathering together of these parts of air by themselves, and by their separation from the parts of water, air comes to be.
Having accepted, therefore, that everything that comes to be from something preexists in it, he further assumed that everything comes to be from everything. Hence he concluded that everything would be mixed in everything else as minute, non-sensible parts. And, because an infinite variety of things can come to be from another, he said that there are infinite, minute parts in each thing.
63. Next, at “but things, as they say” (187b2), he heads off a certain unspoken objection. It is possible for someone to object as follows. If infinite parts of everything are in everything, it would follow that things neither differ from each other nor appear to differ from each other. Therefore, as if he were answering this objection, Anaxagoras says that things appear to differ from each other and are diversely named because of that which is dominant in them, even though there is an infinite number of minute parts contained in any mixture. And so nothing is purely and totally white or black or bone. Rather, that which abounds in each thing seems to be the nature of that thing.
64. Next, at “now the infinite” (187b7), Aristotle refutes the above mentioned position.
Concerning this, he makes two points.
First, he disproves the position absolutely.
Second, at “and it is better” (188a17; [74]), he compares it to the opinion of Empedocles.
Concerning the first part, he makes two points.
First, he sets forth arguments to disprove the opinion of Anaxagoras.
Second, at “the statement that” (188a5; [72]), he disagrees with Anaxagoras’ way of understanding his own position.
Concerning the first part, he gives five arguments.
The first of these is as follows. Every infinite thing is unknown insofar as it is infinite. He explains why he says as infinite. If it is infinite in respect to multitude or magnitude, it will be unknown with respect to quantity. If, however, it is infinite with respect to species (for example, if it is composed of an infinite variety of species), then it will be unknown according to quality. And the reason for this is that what is known by the intellect is grasped by the intellect with respect to all that belongs to that thing. But this cannot happen with regard to something infinite. If, therefore, the principles of a thing are infinite, they must be unknown either with respect to quantity or with respect to species. But, if the principles are unknown, those things that are from the principles must be unknown. He proves this as follows. We think that we know any composite when we know from what and from how many it is composed, that is, when we know both the species and the quantity of the principles. It follows, therefore, from first to last that, if the principles of natural things are infinite, then natural things are unknown either with respect to quantity or with respect to species.
65. At further, if the parts (187b13), he gives the second argument, which is as follows. If the parts of a whole do not have a determinate quantity, either great or small, but can be any size, either great or small, it is necessary that the whole not have a determinate greatness or smallness. Rather, the whole could have any size. This is so because the quantity of the whole comes from the parts. (But this must be understood of the parts existing in act in the whole, as flesh and nerve and bone exist in an animal. Hence he says, by “parts,” I mean components that are actually present and into which a whole can be divided. And by this, he excludes the parts of a continuous whole that are in the whole in potency.)
But it is impossible that an animal or a plant or some such thing be related indeterminately to any size, whether great or small. For there is some quantity so large that no animal exceeds it in size. So also there is some quantity so small that no animal is found to be smaller. And the same must be said of plants. Therefore, by denying the consequent, it follows that the parts are not of indeterminate quantity. For what is true of the whole is true of the parts. But flesh and bone and things of this sort are parts of an animal, and fruits are parts of plants. Therefore, it is impossible that flesh and bone and such things should have an indeterminate quantity, either greater or smaller. Therefore, it is not possible that there should be certain parts of flesh or bone that are non-sensible because of smallness.
66. It seems, however, that what is said here is contrary to the statement that a continuum is divisible to infinity. For if the continuous is divisible to infinity, and flesh is, indeed, a kind of continuum, it seems that flesh is divisible to infinity. Therefore, some part of flesh, according to a division to infinity, goes beyond every determinate smallness. But it must be pointed out that, although a body is divisible to infinity when considered mathematically, the natural body is not divisible to infinity. For in a mathematical body, nothing but quantity is considered. And in this there is nothing repugnant to division to infinity. But, in a natural body, the form also is considered, which form requires a determinate quantity, and also other accidents. Hence it is not possible for quantity to be found in the species of flesh except as determined within some termini.
67. He gives the third argument at “again, according to the theory” (187b21).
Concerning this, he makes two points.
First, he sets forth certain things that are the basis of the argument.
Second, at “for let flesh” (187b27; [68]), he sets forth the deductive order of the argument.
Concerning the first part, he proposes three things.
The first is that, according to the position of Anaxagoras, as was said above, all things are together. And, from this, Aristotle wishes to reduce Anaxagoras’ argument to absurdity. For Anaxagoras said, as was pointed out, that all such things—that is, all things that are of like parts, such as flesh and bone and the like—are in each other and do not come to be from nothing, but are separated from that in which they preexist. And each thing is named from that which abounds in it, that is, from the largest number of parts existing in the thing.