Lecture 8 — A critique of Plato on the soul as a spatial magnitude

Now in the first place it is not well said to say that the soul is a magnitude. For that of the whole, Plato regards as of the same nature as what is sometimes called intellect, not as the sensitive or the appetitive soul; for the movement of these is not circular. Now intellect is one and continuous, as is the act of understanding, which in turn consists of thoughts. But these have unity by succession in a series, like number, not like extension. Therefore, neither is intellect thus continuous; but it is either indivisible or not continuous in the way that a magnitude is.

How would it understand, if it were an extended quantity? As a whole, or by each of its parts? If by its parts, then by an extended part or by a point, if one may call a point a part. If by a point (of which there is an infinite number) it is evident that it will never complete the process. If by an extended part, it will understand the same thing many times over, even to infinity. Yet it seems to do so once for all.

But if it is sufficient that it make contact with any one of its parts, why should it move in a circle or have any magnitude at all? But if it is necessary that it understand by contact with the whole of its circumference, what is the contact it makes by its parts?

Again, how can the divisible be understood by the indivisible, or the indivisible by the divisible?

It is necessary that intellect be this circle; for as the movement of the intellect is to understand, and that of the circle is to revolve, if, then, understanding is a revolving, the intellect must be a circle whose revolving is thinking.

But then it will always think something—since revolving goes on forever. All practical thinking, however, reaches a term, each being for the sake of something else; while speculative thinking likewise is limited by ideas, and every idea is either a definition or a demonstration. But demonstrations begin from principles and have as their term a syllogism or a conclusion. Even if they do not reach a conclusion, they do not come round again to their starting point; they always take a new middle term and conclusion and proceed straight forward. But revolving returns again to the beginning. Definitions too are all finite.

Further, if the same revolving occurs many times over, it will be necessary to understand the same thing many times over.

Moreover, intelligence is better compared with stillness and rest than with motion, and the same holds of syllogistic reasoning.

Again, that will not be happy which is not at ease but forced. But if movement is not of the substance of the soul, it will only move unnaturally.

It must be burdensome for the soul to be entangled with the body without possibility of release; and indeed this should be shunned if it is better for the intellect not to dwell in the body, as is commonly said and as seems true to many.

It is not clear why the heavens move by circular movement; for the substance of the soul is not the cause of the soul moving in a circle, for such movement is only accidental to soul. Still less is the body the cause, but rather, the soul is a cause for the body. Nor is this alleged as for the best; yet the reason why God made the soul revolve must have been because it is more worthy for it to move than to remain stationary and to move in this way rather than in any other. But this speculation is better suited to other contexts, so let us now dismiss it.

Another absurdity arises in this argument and in many others dealing with the soul. They conjoin body and soul, placing the soul in the body without stating anything definite as to the cause of this or how the body is disposed. Yet this explanation is surely necessary, for it is in virtue of something in common that one is an agent and the other acted upon, one moves and the other is moved. No such correlations are to be found at random. These thinkers only endeavor to state what the soul is, without determining anything about the body which receives it, as if it happened that any soul entered any body, as in the fables of the Pythagoreans. For each particular thing seems to have its own proper form and species. It is like saying that carpentry enters into flutes; for each art must use its tools, and each soul its body.

107. Now in the first place (407a2). Having stated Plato’s opinion, Aristotle now proceeds to its refutation.

Here we should note that, often, in criticizing Plato, it is not precisely Plato’s own meaning that Aristotle criticizes, but the obvious sense of his words. He has to do this because Plato’s method of teaching was faulty; he constantly used figures of speech, teaching by symbols and giving his words a meaning quite other than their literal sense, as when he calls the soul a circle. So lest anyone should be led astray by this literal sense, Aristotle sometimes argues precisely against what the words say in criticizing Plato.

108. Against the above-mentioned opinion, then, he brings ten arguments, some of which bear on Plato’s own view and some on the literal sense of his words. Plato did not really mean that the intellect was anything quantitative or circular; he was talking metaphorically. Still, lest there should be any mistake about this, Aristotle argues against a literal interpretation of the words.

109. In the first argument, then, he explains what definition of soul Plato had in mind, that it was the soul of the universe, and that that soul which is of the whole, that is, of the universe, is exclusively intellectual, according to Plato. It is not vegetative, since it needs no nourishment; nor sensitive, since it has no organs of sense; nor appetitive, since appetite follows sensation. Indeed, it could not in any sense be sensitive or appetitive, granted that the movement of this, the universal soul, is circular, because neither sense nor appetite moves in a circle (for sense does not reflect upon itself) but only the intellect (which does reflect upon itself, as when a man knows that he knows). So Plato concluded that the world-soul was only intellectual, and he said that intellect itself was a sort of spatial magnitude and a circle.

110. Aristotle denies this, saying that Plato did not speak well in representing the soul as a spatial magnitude, circular in shape, and in dividing it into two circles.

111. And he points out where Plato went astray. In this matter of the nature of the soul, we have to base our judgment concerning any of its powers upon the act or activity of that power, and our judgment concerning the act or activity upon the object of this act or activity; for powers are known by their acts, and acts by their objects. Thus in the definition of a power is included its act, and in the definition of an act, its object. Now it is clear that a thing gets its unity from whatever gives it being and specific nature. If, then, the intellect gets its being and specific nature from the intelligible which is its object (I speak of the intellect in act, which, as such, is nothing before the act of understanding occurs), it is clear that if it is one and continuous, as Plato held, it will be so in the same way as intelligible objects are one and continuous. For the intellect is one only in the same way as is the act of understanding, which is its activity; and its activity is one only in the same way as its object is one; since acts are differentiated according to their objects.

Since, then, the intellect’s object is intelligible, but these, obviously the intelligibles, compose a unity, not like a magnitude or a continuum, but like numbers which have unity by succession in a series, it is clear that the intellect is not, as Plato thought, a magnitude. It is either indivisible, as it is the nature of first principles to be, (Themistius, In De anima, f. 6vb.) or not continuous in the way that a magnitude is but as a number; for as one number leads to another, so do we understand one object after another. And frequently several numbers terminate in one, as the premises in a syllogism terminate in one conclusion. (Themistius, In De anima, f. 6vb.)

112. The second argument comes at how would it understand (407a10). For it might be answered that Plato’s reason for attributing magnitude to the intellect was not that there are many intelligibles but that each intelligible by itself shows it to be a magnitude.

113. But this will not do. For Plato maintained that the act of understanding was not a reception of species into the intellect, but he thought that the intellect understands through a sort of contact (as of a circle, as we have seen) due to the intellect’s going out to meet the intelligible species.

But I ask you, how precisely does the intellect understand by contact if it is a magnitude? It must touch its object either with the whole of itself or with a part. But if with the whole of itself, then its parts are not needed and there is no necessity for supposing that the intellect is a magnitude or a circle. If, on the other hand, it touches with some of its parts, and thus understands in part, then either several of its parts are involved or only one. If only one, then again the other parts are superfluous, and we need not suppose that the intellect has parts.

But if it understands by touching with all its parts, these must be either points or quantities. If points, then, since the number of points in any magnitude is infinite, the intellect would have to touch its object an infinity of times before it understood the latter at all; and thus it never would understand, since infinity cannot be traversed.

114. Aristotle says “points” not because he thought that a magnitude could be partitioned into points, but as disputing with Plato, who regarded bodies as composed of planes, planes of lines, and lines of points (an opinion refuted by Aristotle in Physics 6, where it is shown that a point added to a point adds nothing). (Aristotle, Physics 6.1, 231a21–b18; cf. Aquinas, Commentary on Physics, bk. 6, lect. 1–2.)

115. But if the intellect understands by touching with quantitative parts, then, as each part is divisible into many, it must understand the same object many times over. Again, since any quantity is infinitely divisible into parts that are proportionately, not quantitatively, the same, it would follow that the intellect understands the same thing an infinite number of times—which raises difficulties. It seems then that it touches its object once only and that it cannot be called a magnitude, either with respect to many intelligibles or to only one.

116. Notice that Aristotle is implying here that intellect is indivisible of its nature. What is intelligible in any thing is its “whatness” or nature, which is present wholly in every part of it, as the specific nature is wholly present in each individual of the species, for the whole nature of man is in each individual man, and the individual as such is indivisible. Hence, what is intelligible in anything is indivisible; and therefore, so is the intellect.

117. The third argument comes at again, how (407a18). Granted that the intellect is indivisible, we can easily see how it can understand both the indivisible and the divisible. For it understands the indivisible in virtue of its own nature, which is indivisible, and it understands the divisible by abstracting it from what is divisible.

But once we allow, with Plato, that intellect is divisible, it becomes impossible to understand how it can understand the indivisible. Hence the difficulty of admitting Plato’s position that the intellect is a magnitude and divisible.

118. The fourth argument begins at it is necessary (407a19). It runs thus. You say that intellect is circular and in movement. Now the movement of circles is a circling and that of the intellect is understanding; hence, if intellect is a circle, understanding must be a circling. But this is false; for, since circular movement has no actual beginning or end, as is shown in the Physics, book 8, it would follow that understanding, the proper act of the intellect, never reached a term. (Aristotle, Physics 8.8, 262a19–b8; 8.9, 265a27–b8; cf. Aquinas, Commentary on Physics, bk. 8, lect. 16, 19, 20.) But understanding has an actual beginning and end: hence it is not the same as circular movement, and therefore, the intellect is not a circle.

119. That understanding has an actual beginning and end can be proved in this way. All thinking is either practical or speculative. Clearly, all practical thinking reaches a term, that is, an end; for it is each being for the sake of something else, namely a work to be done, and in this work it terminates. While speculative understanding too has its end, namely accounts; for it is always limited in certain accounts: either in a definition, when the intellect simply apprehends something, or in demonstration, when it combines and distinguishes things. But demonstrations begin from certain first principles and have as their term a syllogism or a conclusion.

120. If it be objected that one conclusion follows another, and thus there is no definite end, I answer that conclusions are nevertheless not circular. For, as is shown in Posterior Analytics 1, demonstration cannot go in a circle; it always goes in a straight line, and an infinite movement or progression in a straight line is impossible. (Aristotle, Posterior Analytics 1.3, 72b17–73a20; cf. Aquinas, Commentary on Posterior Analytics, bk. 1, lect. 7–8.)

121. Definitions too have a beginning and an end, for you cannot go on to infinity in the enumeration of genera; the most general genus has to be taken as the first one. Similarly, in enumerating species, you cannot particularize to infinity, but must stop at the most specific species. Hence, the most general genus is the beginning, and the most specific species is the terminus or end in definitions. Clearly, then, every act of the understanding has an actual starting point and end.

122. The fifth argument begins at further, if (407a31). In a sense, this argument depends on the previous one and is a part of it. It has been shown that if the intellect were a circle, as Plato thought, understanding would be a circling; and in the preceding argument, Aristotle has shown that understanding is not a circling, which he now proves once more in the following way.

The difference between a circular motion and any other motion lies in this, that the latter can never be repeated on the same quantity. This becomes clear if we think of the different kinds of movement in particular. Thus the movement of alteration cannot be repeated in the same subject in the same respect; for the same thing is not in the same respect changed from white to black and black to white. So, too, in the movement of growth, the same thing cannot in the same respect both increase and diminish. So also in local movement; if this goes in a straight line, it must have two actual terms; and if it is to be repeated, the term at the end of the movement must be used twice, once as end and once as beginning, and, since there must intervene a moment of rest at that term, it is not exactly the same movement. In circular motion alone can one and the same movement be many times repeated according to the same quantity; the reason being that in circular motion there are no actual terms; hence, no matter how often it is repeated, no interval of rest intervenes nor does the motion vary in any way.

123. This being granted, Aristotle argues as follows. If you say that the intellect is a circle, then the act of thinking must be a circular motion. But this consequence is not admissible; therefore, neither is the premise.

124. He then shows that the consequence is not admissible. Granted, he says, that the same revolving occurs many times over, that is, repeated, in the same respect; if thinking, then, is a circular movement, as you say, it will be repeated again and again as one and the same movement bearing upon one and the same object; and so the intellect will think the same thing many times over. For the intellect, in moving, touches, and by this touching, it understands, as they say. If, then, its motion is circular, it touches and understands the same thing over and over again, which gives rise to difficulties.

125. The sixth argument, at moreover, intelligence (407a32), is as follows. If understanding is, as you say, a circular motion, it should be associated with movement, but in fact the contrary is true; understanding is more like rest, so understanding is not a circling.

That it is more like rest than motion Aristotle himself teaches in Physics 7, where he says that someone does not become wise when his motion does not stop and come to rest; this is why boys and all whose motions do not come to rest do not easily become wise. (Aristotle, Physics 7.3, 247b23–24; cf. Aquinas, Commentary on Physics, bk. 7, lect. 6.) Rather, wisdom is acquired when one comes to rest, which is why he says that the soul becomes wise and prudent when resting and sitting still.

126. But lest it be said that, while this is true of simple apprehension, it is not true of syllogistic reasoning, he adds that syllogistic reasoning also is more like rest than movement. And this is clear because, before the syllogism is complete, the mind and intellect is swaying from one conclusion to another and resting in neither, but when it is finished syllogizing, it holds on to one conclusion and rests in it.

127. The seventh argument, at again, that (407a34), runs as follows. It is certain that the soul’s happiness is in understanding. Now, happiness cannot reside in anything violent or contrary to its nature, since it is the soul’s perfection. As, then, movement is not of the soul’s nature and substance, but is contrary to its nature, that activity in which the soul finds its happiness, namely, understanding, cannot be a movement, as Plato maintained. But that movement is against the soul’s nature is implied by Plato’s own position, for he said that the soul was constituted by numbers, and then that it was divided into two circles and was reflected into seven, from which followed movement. (Lect. 4, nn. 46–51; lect. 7, nn. 92–98.) According to this view, then, movement is in the soul not naturally but accidentally.

128. The eighth argument, at it must be burdensome (407b2), goes as follows. It seems to have been Plato’s view that it was not of the nature of the soul to be joined to the body; for he said that it was first constituted of the elements and then compacted with the body, so that it cannot leave the body at will. Well, then, whenever one thing is united against its nature to another, and cannot leave it at will, the resulting state is a punishment; and whenever a thing deteriorates through its union with another thing the union is harmful and to be avoided. But in this hypothesis, the union of soul and body is contrary to the soul’s nature, nor can the soul break away at will; and the result is bad for the soul, as the Platonists commonly say. Apparently, then, union with the body is a punishment and something to be feared by the soul, which is not congruous with Plato’s statement that the soul is composed of elements and mixed with its body from the beginning.

129. The ninth argument, at it is not clear (407b5), is as follows. Plato speaks of the soul of the universe and says it is moved round in a circle. But the cause for the circular movement of the heavens is not clear; that is to say, his opinion does not define the cause of it. For if the heavens are moved in a circle, this must be due either to natural principles or to some final cause.

If natural principles are the cause, the nature in question will be either that of the soul or of the heavenly bodies. But it cannot be on account of the soul’s nature, for circular movement is not of the substance of the soul but is accidental to it; for, as was said, the soul moves through itself and according to its substance in a straight line which is then bent into circles. Nor can the cause be the nature of the heavenly bodies themselves, for the body is not the cause of the soul’s movement, but rather the soul is the cause of the body’s movement.

But, if the cause is for the sake of an end, he cannot point to any determinate end in answer to the question why the heavens move in a circle rather than in any other way, unless one brings in the will of God. God has indeed for a certain reason chosen to move the heavens rather than leave them motionless, and to move them in a circular way. But why he does this Plato cannot tell. However, as this matter is better suited to other contexts, that is, to another treatise (namely, On the Heavens), we can leave it aside for the present. (Aristotle, On the Heavens 2.5; cf. Aquinas, Commentary on Aristotle’s On the Heavens, bk. 2, lect. 7.)

130. The tenth argument starts at another absurdity (407b13). It is effective not only against Plato, but also against many others. It runs thus. It is clear that there must always be some proportion between mover and moved, agent and patient, form and matter. Not every form suits every body in the same way, nor does every agent act upon every patient. Nor, again, does every principle of movement move everything capable of receiving movement. In each case, there must be some correlation and proportion between them by which the one is naturally the mover but the other the moved. Now obviously these philosophers admitted that the soul was in the body and moved it. Since, then, they spoke of the nature of the soul, this explanation is necessary that they should also have had something to say about the nature of the body: about the cause of the soul being joined to the body and how the body is related to and contrasts with the soul. Their study of the soul was inadequate so long as they only endeavored to state what the soul is and neglected to explain the nature of the body that receives it.

131. Indeed, we may associate their thesis (Aristotle goes on to say) with the Pythagorean fable that any soul can enter any body; the soul of a fly for instance might perchance enter the body of an elephant. This cannot in fact happen; for the body of each particular thing, and especially of living things, has its own proper form and species and type of movement: hence, there are great differences between the bodies of a worm, a dog, an elephant, and a gnat. When they say that any soul can enter any body, it is like saying that the art of weaving could enter flutes, or that the art of the coppersmith could enter a weaver’s loom. If it was in the power of these arts to enter bodies or instruments they would not do so indiscriminately, but the art of playing the flute would enter flutes and not lyres, while the art of playing stringed instruments would enter stringed instruments and not flutes. In the same way, if there is a body for every soul, any soul does not enter any body, but rather, the soul shapes the body fit for itself; it does not enter a ready-made body. (Themistius, In De anima, f. 7vb.) Plato and the others who speak only about the soul are too superficial; they fail to define which body answers to which soul and the precise mode of existence of each in union with the other.