Book 1
Chapter 1
We regard knowledge as something good and precious, but we value one kind of knowledge more highly than another, either because of the intellectual insight needed to discover it or because it concerns better and more admirable objects. For both reasons, we should rightly rank the study of the soul among the highest forms of knowledge. Moreover, knowledge of the soul is thought to contribute greatly to all truth, especially to our understanding of the natural world, since the soul is, as it were, the principle of life in living things. Our aim is first to investigate and determine the essential nature of the soul, and second to discover the properties that belong to it incidentally. Some of these properties are thought to be conditions peculiar to the soul’s own nature, while others are thought to be effects that the soul produces in living beings.
It is extraordinarily difficult to reach any settled conclusion about the soul. The problem of discovering a thing’s essence and true definition is common to other fields as well. It might therefore seem that there is a single scientific method applicable to everything whose essence we wish to discover, just as deductive proof applies to incidental properties. If so, we shall have to investigate what that scientific method is. But if there is no single general method for discovering the ultimate nature of things, our investigation becomes still more difficult. Even if the question of method were settled, whether the proper method is deductive proof, analysis, or some other procedure, a very difficult and uncertain question would remain: From what principles should we begin our inquiry? Different subjects employ different principles, as, for example, numbers and plane surfaces do.
Our first task, perhaps, is to determine the genus in which the soul should be classified and what its nature is. That is, we must ask whether it is a particular thing and a self-subsisting entity, or whether it is a quality, a quantity, or something classifiable under one of the other categories already mentioned. We must also ask whether it is a potentiality or, rather, an actuality, since this makes no small difference.
We must further inquire whether the soul is divisible or without parts, and whether every soul is of the same kind. If souls are not all of the same kind, we must ask whether their differences are differences of species or of genus. Those who now discuss and investigate the soul seem to direct their inquiries only toward the human soul. But we must take care to determine whether there is one definition that applies to soul, just as there is one definition that applies to animal, or whether each kind of soul requires a different definition, just as horse, dog, human being, and god each require a different definition. We must also ask whether the common notion “animal” is nothing at all or exists only after the individual animals. The same question could be raised about any other universal notion.
If, however, there are not several souls but only parts of a single soul, a further question arises: Should we examine the soul as a whole before examining its parts? It is also difficult to determine which of these parts differ from one another by nature and whether we should investigate the part before its function. Should we, for example, investigate the process of thought before the faculty of thought, or sense-perception before the organ of sense-perception? The same question applies in other cases.
Suppose that functions should be investigated before faculties. We might then ask whether the corresponding objects should be investigated before the faculties themselves. Should the sensible object, for example, be investigated before the sense organ, and the object of thought before the faculty of thought?
Knowledge of a thing’s essential nature seems to help us understand the incidental nature and properties of substances. In mathematics, for example, knowing the essential nature of the straight and the curved, or of a line and a surface, helps us understand how many right angles are contained in the angles of a triangle. Conversely, knowledge of incidental properties contributes greatly to our understanding of what a thing essentially is. When we can give an account of all, or at least most, of the incidental properties of things as we observe them, we are best able to speak about their essential nature as well. Essential nature is the true starting point of every deductive proof. Definitions that provide no knowledge of incidental properties, and from which it is not even easy to conjecture what those properties are, are clearly framed in a merely dialectical fashion and are empty.
A further difficulty concerns the affections of the soul. Are all these affections shared by the soul and the body that contains it, or is there something that belongs exclusively to the soul? Resolving this difficulty is necessary, though not easy. In most cases, the soul apparently neither acts nor is acted upon independently of the body. This is true, for example, of anger, courage, desire, and, in general, sense-perception. Thought, however, appears more than anything else to be a function belonging exclusively to the soul. But if thought is a kind of representation through a sensory image, or if it cannot occur without such an image, then even thought cannot exist independently of the body.
If there is any function or affection peculiar to the soul, the soul could exist separately from the body. If there is nothing that belongs exclusively to it, however, it cannot exist separately. Its case would then resemble that of a straight line. As straight, a line has many properties, such as touching a bronze sphere at a particular point, although straightness apart from some body does not touch the sphere. Straightness has no separate existence, since it is always joined to some body.
The same seems to be true of the soul’s properties. Courage, gentleness, fear, pity, boldness, joy, love, and hatred are all associated with the body, for when the soul undergoes these conditions, the body is also affected in some way. Evidence for this is that sometimes, when great and obvious misfortunes befall a person, that person is not at all excited or moved to fear. At other times, someone is aroused by slight and insignificant mishaps, and the body swells with rage and enters the condition of a person stirred to anger. The point is supported still more strongly by the fact that, even when nothing has happened that could awaken fear, people sometimes exhibit the emotions characteristic of someone who is frightened.
If this is true, the emotions are forms expressed in the body. We therefore have definitions such as this: “Anger is a particular kind of movement of a particular body, part, or faculty, under a particular stimulus and caused by a particular motive.” For this reason, the study of the soul belongs to the natural philosopher, whether the subject is the soul as a whole or the part of it that concerns the body.
The natural philosopher and the speculative philosopher, however, would define these conditions from different points of view. If asked, “What is anger?” the speculative philosopher might answer that it is a desire for retaliation, or something of that kind. The natural philosopher would say that it is a seething of the blood or heat around the heart. The natural philosopher gives the matter of anger, while the speculative philosopher gives its form or account.
The account is the form of a thing, and if the thing is to exist, that account must be embodied in a particular kind of matter. For example, the account of a house is that it is a shelter protecting us from injury by wind, rain, and heat. The natural philosopher, however, will describe it as stones, bricks, and wood, while the other thinker grasps the account embodied in these materials and the purpose for which they are used.
Which of these, then, is the true natural philosopher? Is it the person who concerns himself with matter but knows nothing of the account, or the person concerned only with the account? The answer is that it is the person who combines both approaches. What, then, is the proper character of each of the other two inquiries?
Surely no one studies only those properties of matter that are inseparable from it, considered merely as inseparable. The natural philosopher deals with all the functions and qualities belonging to bodies and matter of particular kinds. Properties that do not fall within the natural philosopher’s subject are treated by someone else. In certain cases, they are treated by a practitioner of an art, such as a builder or physician. The mathematician deals with properties that are inseparable from bodies but do not belong to any particular body and can be considered abstractly. The metaphysician deals with qualities insofar as they are considered abstract or transcendent entities.
But we must return to the point from which our discussion digressed. We were saying that the properties of the soul do not exist apart from the physical matter of living things in which qualities such as courage and fear are expressed. In this respect, they are not to be regarded in the same way as a line or a surface.
Chapter 2
As we proceed in our inquiry into the soul, we must raise the questions that require answers. We must also collect the opinions of our predecessors who had anything to say about the soul’s nature, so that we may accept what they said truly and guard ourselves against their errors.
The first step in our inquiry will be to set out the attributes commonly supposed to belong to the soul’s nature. Animate nature is thought to differ from the inanimate chiefly in two respects: movement and sense-perception. These, we may say, are the two traditional characteristics of the soul handed down to us by earlier writers.
Some of these writers affirm that motion is the soul’s first and foremost characteristic. Believing that what is itself unmoved cannot impart motion to anything else, they suppose the soul to be something that moves. This is why Democritus declares the soul to be a kind of fire or warm element. He maintains that although atomic structures vary infinitely, both fire and soul are composed of spherical atoms. These resemble the particles we see in the air when sunbeams stream through a doorway. He calls the complete collection of these seedlike particles the elements of the universe.
Leucippus holds a similar view. He says that spherical atoms constitute the soul because such shapes can most easily penetrate everything and, since they are themselves in motion, can move everything else. These philosophers therefore hold that the soul is the principle that imparts motion to animals.
For this reason, they also regard respiration as the function that determines the limit of life. They think that the surrounding air compresses the body and expels the atoms that impart motion to animals because they themselves are never at rest. Respiration brings relief because it allows similar particles to enter the body from outside. By holding back the contracting and compressing force, these incoming particles prevent the spherical atoms already in animals from being completely expelled. Life continues for as long as they can do this.
The theory handed down from the Pythagoreans seems to have the same meaning. Some members of this school maintain that the motes seen in the air in sunlight are the soul. Others declare that the soul is the principle that sets these motes in motion. They appeal to these particles because the particles appear to be in constant motion, even when the air is perfectly calm.
Those who regard the soul as a self-moving principle reach the same conclusion. They all seem to consider motion the soul’s most characteristic attribute. Everything else is moved by the soul, while the soul moves itself. They reached this conclusion because they observed that nothing sets anything else in motion without itself being in motion.
In a similar spirit, Anaxagoras declares that the soul is the principle of motion. The same view is held by any others who assert that Reason sets the universe in motion.
Anaxagoras does not, however, entirely agree with Democritus. Democritus identifies soul absolutely with reason and considers truth to be whatever appears to the senses. Homer was therefore right to sing that Hector lay “with his thoughts gone astray.” Democritus does not treat reason as a distinct faculty for apprehending truth, but asserts that soul and reason are identical.
Anaxagoras is less clear on this point. In many passages he says that reason is the cause of what is beautiful and true, but elsewhere he says that reason is the same as the soul, since it is found in all animals, great and small, high and low. Reason in the sense of intelligence, however, is not found equally in all animals, or even in all human beings.
Philosophers who focus on movement as the principal fact of animate creation conceive of the soul as the most mobile principle. Those who emphasize knowledge and the perception of reality, on the other hand, define the soul as the principle of things. Some hold that there are several such principles, while others maintain that the soul is the only one.
Empedocles, for example, regards the soul as composed of all the elements and asserts that each of these elements is itself a soul. He says:
“We perceive earth by earth, water by water, Divine air by air, destructive fire by fire, And love we know by love, mournful hate by hate.”
In the same way, Plato constructs the soul from the elements in his Timaeus. We know like by like, and things are composed of elemental principles. A similar theory appears in his Discourses on Philosophy. There he defines an animal, considered absolutely, as a structure derived from the idea of unity and from the primary elements of length, breadth, and thickness. Other things are constructed in the same way.
In another formulation, Plato defines reason as one and science as two, since science moves toward unity along a single course. He also defines opinion as the number of a plane surface and sense-perception as the number of a solid. Numbers were declared to be the actual forms and first principles of things and to be composed of the elements. Things are discerned partly by reason, partly by science, partly by opinion, and partly by sense-perception. Numbers, however, are the forms of things.
Because these Platonists regarded the soul as both the principle of motion and the principle of knowledge, some included both ideas in their definition and described the soul as a self-moving number.
These philosophers differ concerning the kind and number of their principles. The greatest difference is between those who regard the elements as bodily and those who regard them as incorporeal. Still others define the elements as a combination of what is bodily and what is incorporeal. They also differ about the number of elements. Some believe there is only one, while others believe there are several, and their definitions of the soul vary according to their theories of the elements.
They included the principle of inherent movement among the primary elements, and not unreasonably. Some philosophers therefore held the soul to be fire, since fire is the finest and most nearly incorporeal of all the elements. Moreover, it most readily receives and imparts motion.
Democritus gave a particularly neat explanation of these phenomena. He says that soul and reason are identical, that they belong to the primary and indivisible bodies, and that they are the principle of motion because of the character of their particles and atomic shapes. Among these atomic shapes, he regards the spherical as the most easily moved, and he says that both reason and fire are composed of particles of this kind.
Anaxagoras, on the other hand, appears to say that soul and reason are different, as we observed above. Yet he treats them as essentially one, except that he regards reason, more than anything else, as the first principle of the world. At any rate, he asserts that reason is the only entity that is absolute, unmixed, and pure. But he assigns both knowledge and motion to this same principle, affirming that reason sets the universe in motion.
According to the traditional accounts of him, Thales also appears to have conceived of the soul as a kind of principle of motion, if it is true that he said a lodestone has a soul because it moves iron.
Diogenes and certain others say that the soul is air, believing air to be the finest element and the ultimate principle. For this reason, they hold that the soul both knows and produces motion. It knows because it is primary and all other things are derived from it. It is the principle of motion because it is the first element.
Heraclitus also says that the soul is the first principle, since it is the fiery vapor from which everything else is derived. It is also the most incorporeal of all the elements and is in constant flux. We apprehend what is moving by means of what is itself in motion, and Heraclitus, like most others, believed that the real world is in motion.
Alcmaeon also appears to have held views about the soul very similar to these. He says that the soul is immortal because it resembles the Immortals, and that it possesses immortality by virtue of its perpetual motion. All divine things are in perpetual motion: the moon, the sun, the stars, and the entire heavens.
Certain cruder thinkers, such as Hippo, asserted that the soul is water. They appear to have based this belief on the nature of animal seed, which is always moist. Hippo argues against those who say that the soul is blood by pointing out that seed is not blood and that seed is the elemental soul.
Others, such as Critias, regard blood as the soul. They suppose that sense-perception is the soul’s most characteristic attribute and that sense-perception is due to the blood.
Thus every element except earth has received at least one vote. No one has represented earth alone as the principle of soul, unless we count those philosophers who regarded the soul as composed of all the elements or as identical with all of them.
We may say that they all define the soul in terms of three things: motion, sensation, and incorporeality. Each of these is traced back to the ultimate elements. Consequently, with one exception, those who define the soul in terms of knowledge make it either an element or something derived from the elements. They say that like is known by like. Since it is the soul that knows all things, the soul must consist of all the elements.
Those philosophers who maintain that there is only one cause and one element regard the soul as a single thing, such as fire or air. Those who maintain that there are several elements make the soul a plurality.
Anaxagoras alone declares that the soul is affected by nothing and has nothing in common with anything else. But if this is its nature, he did not explain, nor is it evident from his writings, how the soul acquires knowledge and virtue.
Philosophers who include contraries among their first principles regard the soul as composed of contraries. Those who include only particular contraries among their principles, such as heat and cold or similar opposites, likewise regard the soul as one of those contraries.
Some thinkers also appeal to the derivation of words. Some claim that the soul is heat because the verb “to live” is derived from heat. Others claim that the soul is cold because the word “soul” is derived from respiration and cooling.
These, then, are the traditional views of the soul, together with the grounds on which they have been advanced.
Chapter 3
We must now turn directly to the investigation of motion. The view that the soul is self-moving and capable of imparting motion may not only give a false account of its essence; it may even be impossible for motion to belong to the soul at all. We have already said that something which imparts motion need not itself be in motion.
Everything that moves does so in one of two ways: it is moved either by something else or by a principle within itself. We say that things are moved by something else when they move because they are within a moving body, as sailors are within a ship. But sailors are not moved in the same sense as the ship. The ship moves by its own nature, while the sailors move because they are within a moving vessel. This is clear from considering the parts of the body. Walking is a motion peculiar to the feet, but it is also an attribute of a human being, though it is not an attribute of the sailors at the moment in question.
Since motion is spoken of in two senses, let us investigate the soul and ask whether it moves itself or merely participates in movement. There are four kinds of movement: change of place, qualitative change, decay, and growth. The soul’s movement, then, must be one of these, several of them, or all of them. If the soul is not moved accidentally, motion must be one of its natural attributes. If so, space must also be an attribute of it, since all the movements just mentioned are spatial. If the essential nature of the soul is self-movement, its movement will not be accidental, as the movement of a white object or of an object three cubits long is accidental. In those cases, what moves is the body, while whiteness and a length of three cubits are merely attributes of it. Space therefore does not belong to those attributes. But space will be an attribute of the soul if the soul by its own nature participates in motion.
Again, if the soul moves by its own nature, it can also be moved by external force; and if it can be moved by external force, it can also be moved by its own nature. The same conditions apply to rest. An object naturally rests in the state into which it naturally moves. Likewise, when an object is forcibly moved into a certain state, it also rests there by force. It is difficult even to conjecture what forced motion and forced rest in the soul would be like.
Again, if the soul’s movement is upward, it will be composed of fire; if its movement is downward, it will be composed of earth, since these movements are characteristic of those elements. The same reasoning applies to the intermediate elements.
Since the soul evidently sets the body in motion, it is reasonable to suppose that it also experiences the movements it imparts. If this is true, the converse must also be true: the soul experiences the motion experienced by the body. Now the body moves through space. The soul should therefore change place as the body does, with either the entire soul or some of its parts changing position. If this were possible, the soul could also reenter the body after once leaving it. The impossible conclusion would follow that dead animals can come to life again.
As for accidental movement, the soul could be set in motion by an external body. An animal might, for example, be pushed by an external force. But we must not suppose that something essentially self-moving is moved by anything else except accidentally, just as the absolute or final good cannot be the relative or secondary good.
If the soul is moved at all, one would say that the objects of sense cause its motion more than anything else does. Yet if the soul moves itself, it must itself undergo motion. Therefore, if every movement is a displacement of the moving object insofar as it is moved, the soul must be displaced from its essential nature, provided that its self-motion is not merely accidental. But motion is supposed to belong to its essential nature.
Some thinkers, including Democritus, speak in a spirit like that of the comedian Philippus and say that the soul moves the body in which it resides just as it moves itself. Philippus tells us that Daedalus made his wooden statue of Aphrodite move by pouring quicksilver into it. Democritus says much the same thing when he tells us that spherical atoms, which are never at rest, move the whole body by their pulling and pushing. But we must ask whether these same particles also produce rest. It is difficult, or altogether impossible, to say how they could do so. In short, the soul does not appear to move the body in this way, but rather through some act of volition or thought.
Similarly, the Timaeus gives a natural explanation of how the soul moves the body: because the soul moves itself, it also moves the body with which it is intimately bound. The Timaeus regards the soul as composed of the elements and divided into parts corresponding to harmonic numbers, so that it may have an innate perception of harmony and possess harmonic movements in its entirety. Thus, in the Timaeus, the straight line is bent into a circle, then divided into two circles joined at two points, and the original circles are further subdivided into seven others, on the supposition that the heavenly orbits correspond to the movements of the soul.
Against this view, one may say first that it is incorrect to describe the soul as a magnitude. By the soul of the universe, he evidently means something like what we call reason. At any rate, it cannot be the sensitive or appetitive soul, since their motion is not circular. But reason is one and continuous, as the process of thought also is. The process of thought consists of thoughts, and these form a numerical unity through their succession, not a unity in the sense of magnitude. Reason, therefore, is not continuous in the sense of magnitude either. It is either indivisible or at least not continuous as a magnitude is.
For how could reason think if it were a magnitude? Would it think as a whole or by means of one of its parts? If by means of one of its parts, that part must be either a magnitude or a point, if a point can properly be called a part. If it thinks as a point, and the points are infinite in number, it will clearly never reach a conclusion. If it thinks as a magnitude, it will think the same thing many times, or infinitely many times. Yet it appears possible to think something once and for all.
If contact by any one part of the soul is sufficient, why must it move in a circle or possess any magnitude at all? But if thought requires contact throughout a complete circle, what is the significance of contact in any particular part? Again, how is the soul to think what is divisible by means of what is indivisible, or what has no parts by means of what does have parts?
Reason, however, must be a circle of this kind if thought is the movement of reason just as revolution is the movement of a circle. If thought is a revolving movement, reason must be a circle whose revolving movement is thought. Furthermore, reason must always be thinking something if circular motion is perpetual.
But this cannot be true. Thoughts that result in conduct have definite limits, since they are all determined by an end, while speculative thoughts are determined by logical processes. Every logical process is either a definition or a demonstration. Demonstrations begin from a premise and reach some kind of termination in a syllogism or conclusion. Even if they do not result in a conclusion, they still do not return to their premise or starting point. Instead, they continually take a new middle term and a new extreme term and thus proceed in a straight line, whereas circular motion returns to its starting point. Definitions, too, are all determinate.
Moreover, if a rotation completes itself several times, one will necessarily think the same thought several times. Thought also seems more like rest and concentrated attention than motion, and the same applies to a syllogism.
Furthermore, whatever is difficult or contrary to nature cannot be pleasurable. If motion is not an essential property of the soul, the soul must move contrary to its nature. It must therefore be painful for the soul to be united with the body from which it cannot free itself. Such a union must even be avoided if it is true that reason is better off when separated from the body, a view commonly held and accepted by many people.
The cause of the circular movement of the heavens is also unclear. Circular movement certainly does not arise from the essential nature of the soul, since the soul moves in this way only accidentally. Nor does it arise from the body, since the body’s motion is due to the soul. On the other hand, this motion is not attributed to the soul on the ground that circular movement is better. Yet that is precisely why God must have endowed the soul with circular movement: first, because motion is better than rest, and second, because circular movement is better than every other kind. Since this inquiry more properly belongs to other branches of knowledge, let us set it aside for now.
We may, however, note a contradiction found in this and in most other theories of the soul. They attach the soul to the body and place it within the body without determining why this should be so or explaining how the body is related to the soul, though it would seem necessary to know this. Because of this union, one acts and the other is acted upon; one receives motion and the other imparts it. Such correlations are not found between things whose association is merely accidental.
These theories merely try to explain the nature of the soul and offer no account of the body that receives it. In the spirit of the Pythagorean myths, they suppose that any soul can clothe itself in any body. But this cannot be true, since every body appears to have its own distinct form and character. Their doctrine is much like saying that the carpenter’s art clothes itself in flutes, whereas an art employs its own instrument just as a soul employs its own body.
Chapter 4
Another theory of the soul has been handed down from our predecessors. To many people, it is no less convincing than the theories already described, and it has even been discussed in our popular treatises. This theory regards the soul as a kind of harmony. Its advocates say that harmony is a mixture and combination of opposites and that the body, too, is composed of opposites.
Although harmony is indeed a certain relation among mixed parts or a combination of parts, we maintain that the soul cannot be either of these. Again, motion is not an attribute of harmony, yet nearly all the philosophers who support the theory of harmony attribute motion to the soul. Another objection is that the word harmony is more appropriately applied to states of health or to bodily qualities in general than to the soul. This becomes especially clear when one tries to describe the effects and functions of the soul in terms of harmony, since it is difficult to find any correspondence between them.
We may have two kinds of harmony in mind when we use the term. In its primary sense, harmony means a composition of magnitudes in things that possess motion and position, such that the parts fit together and admit nothing further of the same kind. In its secondary sense, harmony is a ratio among mixed elements. But in neither sense does harmony apply to the soul.
The composition of the body’s parts can be readily examined. There are many combinations of these parts, and they may be produced in many ways. Of what parts, then, is reason a combination, and how is that combination produced? The same question applies to the sensitive and appetitive soul.
It is equally absurd to regard the soul as a ratio of mixture. The elements are not mixed in the same ratio when they form flesh as when they form bone. If every part of the body is composed of mixed elements, and if the ratio of the mixture constitutes harmony and soul, the absurd result is that we possess many souls distributed throughout the entire body.
One might demand an answer from Empedocles on this point, since he says that each of these mixtures of elements is determined by a given ratio. The question is whether the soul is this ratio or something else produced in the bodily members. Again, is Love the cause of any chance mixture, or only of a mixture that observes a fixed ratio? And is Love itself this ratio, or is it something that transcends the ratio and differs from it? These, then, are the difficulties involved in this theory.
If the soul differs from the mixture or combination, why is the soul annihilated at the same moment as the flesh and the other parts of the living being cease to exist? Furthermore, if each part does not have a soul because the soul is not the ratio of mixture, what is destroyed when the soul leaves the body?
It is therefore clear from the preceding arguments that the soul cannot be regarded as a harmony, nor can its motion be regarded as circular. It is possible, however, for the soul to be moved accidentally and in that sense to move itself. For example, that in which the soul exists may be moved, and this in turn may be moved by the soul. But the soul cannot move spatially in any other way.
One might more reasonably raise objections to the soul’s movement by considering the following facts. We speak of the soul as feeling pleasure, pain, courage, fear, and anger, and as perceiving and thinking. All these processes apparently are movements, and on this ground one might suppose that the soul is moved.
But this does not necessarily follow. Even if feeling pleasure or pain and the process of thinking are movements in the fullest sense, and even if each of them is a movement, the movement may be produced by the soul. Anger or fear, for example, may be produced by a particular movement of the heart, and thinking by a movement of either this kind or some other kind. Some of these movements are changes of place, while others are processes of qualitative change. What particular kinds they are and how they are produced must be considered elsewhere.
To speak of the soul as feeling anger, however, is like speaking of the soul as weaving or building a house. It is better not to say that the soul feels pity, learns, or thinks, but that the person does these things through the soul. We must not suppose that this is because movement occurs within the soul. Rather, movement sometimes proceeds to the soul and sometimes proceeds from it. In sensation, for example, movement proceeds from external objects; in recollection, movement proceeds from the soul toward excitations or fixed impressions that remain in the sense organs.
Reason appears to be an entity implanted in the soul and incapable of being destroyed. If it were perishable, it would be destroyed by the decay of old age more than by anything else. But what actually happens is the same as with the sense organs. If an old man could have the eye of a young man, he would see as well as the young man. Old age, then, does not arise because the soul has undergone some change. The change occurs in the soul’s organ, the body, as also happens in drunkenness and disease.
