Lecture 7 — Democritus and Plato on the soul as a mover of the body

Some say that a soul moves the body in which it dwells just as it is itself in motion, as, for example, Democritus, who spoke like Philip the comic poet; for the latter relates that Daedalus made a wooden Venus mobile by pouring quicksilver into it. Democritus, then, spoke in like manner, saying that there are in movement indivisible spheres of which the nature is to be never at rest and which therefore draw together and move the whole body.

Now, what we would ask is whether this is also the cause of coming to rest. How it could be, on this hypothesis, is difficult to see—indeed impossible.

The soul seems, in general, not to move the animate being in this way, but by a certain will and understanding.

In the same way, the Timaeus sets out a physical theory as to how the soul moves the body. For from the fact that the soul moves, it moves the body as a result of its connection with the body.

For it is compounded of the elements and divided according to harmonic numbers, so that it has a connatural sense of harmony, and the whole is borne along with well-attuned motions:

He bent the straight line into a circle, and, dividing it, made two circles, adjusted at two points, out of one; and again, he divided one of these into seven circles, as though the heavenly motions were the soul’s motions.

87. Some say that a soul moves the body (406b15). Having argued in a general way against the view that movement pertains to the soul in virtue of itself, (Lect. 6, nn. 75–86.) the Philosopher now brings forward arguments against particular philosophers whose theories of the movement of the soul seem to give rise to some special difficulty. These arguments fall into three groups.

First, he opposes an opinion of Democritus;

second, at in the same way (406b25; [91]), one of Plato;

and third, at there is another opinion (407b27; [132]), another theory.

Concerning the first, he does two things.

He begins, then, by stating the view of Democritus on the soul’s movement;

and then he brings objections against it.

88. This theory has already been referred to by Aristotle in his fourth objection to the view that the soul moves in itself and by this movement makes the body move. (Lect. 6, nn. 81–83.) If the soul moves the body, he has said, it must do so in virtue of its own movement. This was admitted by some who said that each soul moves the body in which it dwells just as it is moved itself, that is, with those motions by which it is moved itself; among whom was Democritus, who made use of the following illustration.

There was a certain comic dramatist called Philip who tells somewhere of one Daedalus, that he made a wooden statue of the goddess Venus, and that this statue, being filled with quicksilver, was able to move. It moved as the quicksilver moved. And what Democritus said of the soul’s movement was rather similar. The soul, he said (as has been noted above), was composed of indivisible spheres or atoms which, being round in shape, were always moving about, and by their incessant movement made the whole body cohere and move accordingly. (Lect. 3, n. 34; lect. 5, n. 56.)

89. Then, at now, what we (406b22), Aristotle puts two objections to this opinion of Democritus.

First, it is agreed that in animals the soul is the cause of resting as well as the cause of movement. But according to Democritus the soul is never the cause of rest, though it is the cause of animal movements. For it is difficult to see—indeed impossible that those spherical atoms ever rested if they never cease to move.

90. Again, at the soul seems (406b24), he puts a second objection. The movement caused by quicksilver in the statue is obviously not voluntary; it is a compelled movement. On the contrary, that of the soul is voluntary, proceeding from will and understanding. Hence the view of Democritus seems worthless.

91. Then, at in the same way (406b25), he states the opinion of Plato, concerning which he does two things:

first, he states the opinion of Plato;

second, he rejects it, at now in the first place (407a2; [107]).

Concerning the first, he does two things:

first, he shows the similarity of the Platonists’ opinion to the theory of Democritus;

second, he explains what Plato said about the soul, at for it is compounded of the elements (406b28; [92]).

Therefore, he says first that, as Democritus had supposed that the soul’s movements moved the body to which it was joined, so also did Timaeus, a speaker introduced by Plato. For he said that soul moves body insofar as soul itself is moved; because the two are, as it were, bound up together.

92. Then, when he says, for it is compounded (406b28), Aristotle makes Plato’s view explicit:

first, as to what constitutes the substance of the soul;

second, at he bent (406b31; [99]), as to how movement proceeds from it.

Regarding the former question, note that the words quoted here are used by Plato in the Timaeus and refer to the soul of the world which, according to him, is imitated by inferior souls. (Plato, Timaeus, 34b–57c.) So when he touches, as here, on the nature of the world-soul, he refers also, in a way, to any soul. Now Plato, for the reason already given, maintained that the substance of all things was numerical, and that in number the formal element, so to say, was one, and the material element, two—all numbers being made up of one and two. (Lect. 4, nn. 46–51.) And as odd numbers retain something of the indivisibility of one, he laid down two elements of number, the even and the odd, attributing identity and finitude to the odd, but difference and infinity to the even.

93. Some explanation of this theory may be found in the Physics, book 3. (Aristotle, Physics 3.4, 203a10; cf. Aquinas, Commentary on Physics, bk. 3, lect. 6.) If odd numbers are added to unity in sequence, the same type of number always results; for example, if three, the first odd number, is added to one, you get the square number four; if to four you add the second odd number, five, you get nine, which is also a square number; and so on to infinity. But with even numbers the result is always a different type of number. Add two, the first even number, to one, and the result is the triangular number three; to which, if you add four, the second even number, you get seven, which is septangular; and so on to infinity.

Hence, Plato made identity and difference the first elements of all things, attributing the former to odd numbers, the latter to even.

94. And because he placed the soul midway between the higher substances, which never change, and corporeal substances, which change and move, he thought that the soul was constituted of the elements of identity and difference, and so of odd and even numbers. For the mean must participate in both extremes. This is why Aristotle says that Plato held the soul to be compounded of these elements (406b28).

95. Again, we should note that in numbers there are different proportions and infinite numbers, of which some are harmonic, that is, the cause of harmony. The double proportion causes the harmony called a whole octave; that of three to two causes the harmony called a fifth; that of four to three causes the harmony called a fourth; that of nine to eight causes a tone; and the other harmonies are caused by other proportions: for example, the harmony composed of an octave and a fifth is caused by the triple proportion; that of the double octave is caused by the quadruple proportion.

This was discovered by Pythagoras, as Boethius relates in Music, from the striking of four hammers which sounded in harmony according to the aforesaid proportions. (Anicius Manlius Severinus Boethius (ca. 480–524 AD), De institutione musica, bk. 1, ch. 10.) Thus, if one hammer weighed twelve ounces, one nine, one eight and one six, the one that weighed twelve ounces would be in the proportion of two to one to the hammer weighing six, and the two together would render the harmony of the octave.

Again, the hammer weighing twelve ounces would be as three to two to the hammer that weighed eight, and the harmony produced would be that of a fifth; similarly in the case of those that weighed nine ounces and six ounces.

Again, the hammer weighing twelve ounces is in the proportion of four to three to the one weighing nine, and it makes with it the harmony of a fourth; so also does the one that weighs eight with that weighing six; while the one weighing nine is proportioned to the one that weighs eight and produces with it the harmony called a tone.

96. But though Plato said that everything is made up of numbers, he did not say these were numbers with harmonic proportions; but he did say that the soul is made up of numbers having these proportions.

Hence, Aristotle gives it as Plato’s view that the soul was divided, or, as it were, weighed out, according to harmonic numbers, that is, to numbers related to each other in musical proportions.

He said that the soul was constituted of the numbers one, two, three, four, eight, nine, and twenty-seven, in which these harmonic proportions are found.

97. And he had two reasons for thinking this. One was the fact that similarity and connaturality are always a cause of pleasure. We find the soul taking pleasure in all harmonies and disliking whatever is unharmonious in sounds and colors and indeed in any sensible quality. So harmony seems to be natural to the soul. This is what he means by saying that the soul has a connatural sense (that is, knowledge) of harmony.

98. The second reason is that the Pythagoreans and Platonists thought that beautifully harmonious sounds resulted from the movements of the heavenly bodies; and since they supposed these movements to be caused by the world-soul, they naturally concluded that the soul was made up of harmonic numbers. Hence, Aristotle says, that the whole (that is, the universe) is borne along with well-attuned motions.

99. Next, when he says, he bent (406b31), Aristotle explains how the world-soul is the cause of heavenly movements. Taking all numbers in their natural order, we must think of them as laid in a straight line, each one adding to the preceding one. Now the natural numerical series can give rise to several other series; for example, one might take the geometrical series whose common ratios are two or three or four, and so on for other ratios.

As, then, man, by thought, can manipulate numbers, so does God in building up the substances of things from numbers. In constructing the soul’s substance out of the aforesaid numbers, namely, all those placed in a straight line series according to their natural order, he divides them into two series: one, the geometrical series whose common ratio is two; the other, the geometrical series whose common ratio is three; because these two embrace all the harmonic proportions. For the double proportion is divided into the ratios 3:2 and 4:3; the triple into 2:1 and 3:2.

Therefore, the above-mentioned numbers are taken, in the geometrical series with common ratio two, up to the first cube number, for example, one, two, four, up to eight; so also with the series with common ratio three, for example, one, three, nine, twenty-seven. These two series meet at unity like two straight lines containing an angle.

100. Moreover, if the numbers in the series whose common ratio is three are joined to unity we get as a result the numbers of the series whose common ratio is two; for example, if to one is added three, the result is four. Conversely, if to one is added two, the result is three. Thus it is as if two lines were drawn intersecting each other like the Greek letter X.

101. If we proceed further, we return to the same numbers. For from four we go on to eight and from three to twenty-seven, both series concluding with the same type of number, as though we were going round in a circle.

102. We must realize that for Plato the more complex things found in nature are composed of simpler natures, just as the harmonies of sounds arise from the proportions between numbers. He put the substance of the soul midway between numbers, which are eminently abstract, and sensible substances; and so he deduced the soul’s properties from the said numbers. Thus, in the soul we find, first, a direct knowing, in that it looks directly at its object; and then the circular return by which the intellect reflects upon itself. So, too, the intellectual soul moves in a sort of circle with respect to the even and the odd in knowing things both like and unlike itself. And this principle is extended to the substance of the visible heavens moved by the world-soul.

103. For in the heavens we find two circular movements. One is simple and uniform by which the heavens move or revolve daily from east to west according to the equinoctial circle. The other is that of the planets, which is from west to east according to the circle of the zodiac, which intersect the equinoctial circle at two points, namely, at the beginning of Aries and Libra, but decline the most from the equinoctial circle at the two points of solstice, that is, at the beginning of Cancer and of Capricorn.

104. And since the former motion is uniform, it is not divided into several motions; and in this it resembles the circle of the odd numbers; which is also why it is the greatest circle; for the odd numbers referred to are greater than the even.

105. The second motion, however, is very much diversified, and seems therefore to answer to the circle of even numbers. It divides into seven circles according to the intervals between the numbers in the two series of multiples of two and of three, as is said in the Timaeus. (Plato, Timaeus, 36d.) Where there are six points of division there must be seven parts divided off. Hence these circles are smaller and are contained by the highest circle, which is that of the odd numbers.

So the text is to be interpreted thus: as the whole, that is, the universe, is borne along with well-attuned motions, that is to say, as the harmonized movements of the heavens are due to the harmony of the world-soul, God bent the straight line into a circle in the manner described, according to the properties of number and of the soul; and dividing this one circle—which is one by the unity of the natural series of numbers or by the intellectual power of the soul—into two circles, he forms the pair of numerical circles, the odd and the even, and the pair of circles in the soul, the understanding of moving and of motionless objects, and the pair of heavenly circles, the equinoctial and zodiacal motions.

106. He adds, however, adjusted at two points, because any two intersecting circles touch each other at two points. And again one, that is, the inferior one, he divided into seven circles, as if of the planets, as though the heavenly motions were the soul’s motions, that is, as if the heavens moved by the movement of the world-soul.