1. Biographical Information

Plato was born in Athens c. 428/7 BCE, and belonged to a distinguished Athenian family. As a young man he had a close association with Socrates. He describes him as "the most just man of his time" (VIIth Letter 324e). After the fall of the "Thirty" in 403 BCE (This revolutionary, aristocratic government came to power in 404 BCE), Athens became democratic once again. But some in power—Anytos in particular—brought accusations against Socrates, which Plato considered to be spurious (see Apology). Nevertheless, Socrates was executed for his alleged crimes, after which Plato left Athens and went to Megara. Later, he traveled to Egypt, Magna Graecia and Sicily, where, it seems, he became acquainted with Pythagoreanism. Returning to Athens, Plato founded his own school, in the groves near the gymnasion at Acadêmos. During his three visits to Sicily, Plato attempted to convince the older and younger Dionysios to implement reforms consistent with his ideal system of government, but was unsuccessful. He died in his eightieth year.

2. Plato's Doctrine of Ideas and the Soul

The tentative epistemological conclusions in the dialogues Theaetetus and Cratylus anticipate Plato's doctrine of Ideas (ideai or eidê) (Plato's "Ideas" are often called "Forms," since forma is the Latin translation of idea or eidos.) His doctrine of Ideas is inseparable from his conception of the soul, since the soul is what knows the Ideas. Aristotle reports that Socrates sought after universal definitions. The question that Plato asked is what is the ontological status of these universal definitions and how is it that human beings can know these?  His answers to this question constitute his teaching about Ideas and the soul. The best approach to this investigation is to examine relevant dialogues or parts thereof where these two concepts are discussed at length.
 

2.1. Phaedo

2.1.1. The Philosopher and Death (Phaedo 59c-70c)

In the dialogue Phaedo, Socrates is speaking with some of his friends and followers in the last hours of his life. Fittingly, the question that he undertakes to investigate is whether the soul (hê psuchê) is immortal. Socrates affirms that the man who has devoted himself to philosophy should be cheerful in the face of death, for, during his whole life, the philosopher has been preparing himself for death (Phaedo 59c-70c). The philosopher's goal has been to become as independent of the body as possible, so that death is really only the ultimate independence of the soul from the body. During this discussion, Socrates explains that it is the soul alone that can understand absolutes (things themselves)—"the essence or true nature of everything" (apantôn hê ousia)—such as justice, beauty or good; the body with its sense organs can only perceive individual things, not the absolutes insofar as they inhere in the individual, but the absolute truth (alêthestaton) of the individual thing. (Phaedo 65d - 66a)  Socrates then advises that one ought to be rid of all bodily distractions as much as possible, in order to become wise, because wisdom consists in the soul's knowledge of absolutes. It follows that death will be an advantage to the philosopher, because no longer will the body be able to distract the soul.

2.1.2. Arguments for the Immortality of the Soul (Phaedo 70c-80c)

Upon hearing of Socrates's discourse on the philosopher and death, Cebes asks whether Socrates knows that the soul can actually survive death; it is one thing to say that the soul is impeded by the body but something else to prove that it survives its dissolution. There follow three arguments for the soul's immortality.

    First, Socrates argues that, since opposites are generated from opposites that life must be generated from death. Since the principle of life is the soul, then the soul must survive death, or else life would soon cease. (Phaedo 70d - 72a) (This is the basis of belief in the reincarnation of souls.) Second, Socrates argues that, since learning is recollection, the soul must have pre-existed or else there would be nothing to recollect; when the soul enters the body it "forgets" what it once knew and must "recollect" it.  Added to this is the fact that human beings have an innate knowledge of the things themselves, by which is meant absolutes or general concepts by which to judge sense data. These they recollect as they receive sense data. For example, one needs to have knowledge of "equality itself" (auto to ison) to be able to judge two objects to be equal or unequal in some respect.  Socrates concludes that the knowledge of these absolutes are innate in the soul, although such knowledge has been forgotten, from which it follows that the soul must pre-exist its incarnation in the body. (Phaedo 75c - 76c)  Thirdly, Socrates argues that, since it is like the Ideas in its invisibility and incorporeality, the soul must also be incomposite as they are, which means that the soul is incorruptible. In this context, Socrates contrasts the realm of invisible, unchanging absolutes with that of the realm of the visible and changing material exemplifications of these absolutes. To the former belongs the soul, while to the latter belongs the body. When the soul contemplates the absolutes, being free from the impediments of the body, it enters into the condition of understanding (phronêsis). Socrates describes this as passing "into the realm of purity, and eternity, and immortality, and unchangeableness." (Phaedo 78c - 79d)

2.1.3. The Body and the Soul (Phaedo 79d - 84b)

Socrates explains that, upon the death of the body, the invisible soul goes to the realm of invisible, pure and noble, into the realm of the good and wise God: "But the soul, the invisible, which departs into another place which is, like itself, noble and pure and invisible (gennaion kai katharon kai aidê)—the true Hades or unseen world—to the realm of the God of the other world in truth, to the good and wise God, to where, if God will, my soul is soon to go, —is this soul, which has such qualities and such a nature, straightway scattered and destroyed when it departs from the body, as most men say?” (80d). This is the natural abode of the soul apart from the body. If it has remained uncontaminated by contact with the now-deceased body, then the soul may remain in this realm. Souls that are so contaminated, however, return to the realm of the visible and changing to be reincarnated. The philosopher is the one whose soul is able to go beyond the realm of the visible, and see the true reality, which is intellectual and invisible: "that which is shadowy and invisible to the eyes but is intelligible and tangible to philosophy" (81b). Souls that practice philosophy attain to the divine nature and will enter into communion with the gods (Phaedo 82c).

2.1.4.  Ideas as Causes (Phaedo 99c - 105b)

Socrates argues that things in the realm of the visible and changing are what they are insofar as they participate in the Ideas; they cause things to be what they are, allowing individual things to be identified as an instance of the universal or thing itself. Beautiful things are beautiful because they participate in (metechein) beauty itself. He says, "For I cannot help thinking that if there be anything beautiful other than absolute beauty, that can only be beautiful in as far as it partakes of beauty itself (or absolute beauty)-and this I should say of everything" (100c). These things themselves or absolutes are named Ideas, and visible and changing things that bear the name of an Idea are so named because they participate in that Idea. This is Plato's theory of causation (aitia): the Ideas cause individual things in the visible world to be what they are. (Phaedo 100b - 100e)
 

2.1.5. The Soul as Partaking of the Idea of Life (Phaedo 105b - 107a)

Socrates argues further that the soul is immortal because it participates in the Idea of life, thereby giving the body life; if the soul participates in Idea of life it must be immortal, since opposite Ideas cannot co-exist.
 

2.2. Phaedrus

In the midst of a rather distasteful discussion of homosexual love, Socrates expounds on the soul and beauty itself. Reversing his earlier position that love (eros) is an evil, Socrates now argues that the madness of love is the greatest of the blessings of heaven. The love of physical beauty is the first step towards a knowledge of a love of beauty itself.  As a preliminary to his establishing this position, Socrates discusses the soul.
 

2.2.1. The Immortality of the Soul (Phaedrus 245c - 246a)

Socrates affirms that the soul is immortal, because it is the nature of the soul to be self-moving and therefore eternally moving: "For that which is ever in motion is immortal" (to gar aeikinêton athanaton). It is the nature of the soul to be immortal, since motion is life and the soul is the principle of life. In addition, the soul is the first principle of motion (archê kinêseôs) in the body; without the soul there can be no motion. Since a first principle is unbegotten, it is indestructible. The soul as first principle of bodily motion, therefore, is unbegotten and indestructible. (Phaedrus 245c - 246a).
 

2.2.2. The Chariot Metaphor  (Phaedrus 246a - 250c)

Socrates turns his focus on the nature of the soul. He compares the soul to a winged charioteer who controls two winged horses, one good and the other evil, representing the good and evil natures of human beings. The winged charioteer, like the gods, should aim to ascend to the highest sphere, beyond the heavens, where she will behold Being itself or "truly existing existence" (ousia ontôs ousa), "with which true knowledge is concerned; the colorless, formless, intangible essence, visible only to mind" (achrômatos te kai aschêmatistos kai anaphês...psuchês kubernêtêi monôi theatê nôi, peri hên to tês alêthous epistêmês genos) (247c). As the sphere rotates, the soul sees also "justice, and temperance, and knowledge absolute, not in the form of generation or of relation, which men call existence, but knowledge absolute in existence absolute (tên en tôi ho estin on ontôs epistêmên ousan)" (247d - 247e). It is not, however, that the soul beholds the absolutes for the first time, because, being immortal, the soul has already had a contemplation of "Being itself." Socrates says, "For, as has been said, every soul of man has by nature beheld the beings" (pasa men anthrôpou psuchê phusei tetheatai ta onta) (249d - 250a); when the soul in its embodied state manages to grasp the highest reality, it is only recalling what it already knew. It is clear that this "myth" is intended to communicate the distinction between the realm of the visible and changing from that of the intelligible and unchanging. The soul's task is to apprehend the latter, in spite of the hindrance of  the body. Moreover, it seems that ontologically (as opposed to spatially) beyond the realm of Ideas is Being itself (or "truly existing exisence"), which has no qualities at all, being beyond all distinctions. Those souls that behold "Being itself" will escape from the necessity of rebirth into the realm of the visible and changing.  (Phaedrus 246a - 248c).
 

2.3. Republic 5-7

The doctrine of Ideas finds its most complete expression in Republic 5-7; the discussion up to Republic 5 deals mostly with political and social issues, but in Republic 5-7 the conversation turns towards the nature of philosophy and the philosopher. This is because Plato's ideal ruler is the philosopher-king: To be a good ruler one must be a philosopher. Necessarily, therefore, Plato must describe what a philosopher is.

2.3.1. Republic 5

Towards the end of Republic 5, Socrates, acting as Plato's literary mouthpiece, says that the philosopher are "lovers of the visions of the truth" (475e). He then differentiates between knowledge (gnôsis) and ignorance (agnôsia): the former has Being (to on) for its subject-matter or object, while the latter has non-Being (to mê on). In other words, to know is to know what is, while not to know is to "know" nothing, which is really impossible. There is, however, an intermediate cognitive faculty, which Socrates calls opinion (doxa); it stands between knowledge and ignorance partaking of both. The subject matter or object of opinion likewise partakes of both being and non-being. To opine is to recognize the participation of the objects of perception in the things themselves or absolutes but without being to recognize the absolutes themselves. For example, a man may perceive and name many beautiful things, but not be aware of beauty: "Then those who see the many beautiful (polla kala), and who yet neither see beauty (to kalon), nor can follow any guide who points the way thither; who see the many just, and not justice, and the like—such persons may be said to have opinion but not knowledge?"  (479e)  Opinion is what Plato calls knowledge of the manifestations of the Ideas in the sensible world, but without differentiating the Ideas from that which which participate in the Ideas. The objects of opinion are in constant flux, so that opinion by its very nature is impermanent; this is why it cannot be knowledge, because knowledge has for its object what is permanent (Being). But because it recognizes the presence of the Ideas in sensible world, opinion cannot be called ignorance either. (Republic 5 [473c - 480])
 

2.3.2. Republic 6

In Republic 6, Plato expands upon his philosophical reflections begun in the previous chapter. Socrates continues his discussion of the nature of the philosopher, who, ideally, will rule the State. He is defined as one who is able "to grasp the eternal and unchangeable" (hoi tou aei kata tauta hôsautôs echontos dunamenoi ephaptesthai) (484b), and not be one who wanders "in the region of the many and variable." (484b). The philosopher is one who contemplates the absolutes and is not content to live in the realm of perception. Further defining him, Socrates says that the philosopher loves "knowledge of a sort which shows them the eternal nature not varying from generation and corruption" (485b) (ekeinês tês ousias tês aei ousês kai mê planômenês hupo geneseôs kai phthoras).   In other words, the philosopher seeks to know the Ideas. By contrast, Socrates says that the non-philosopher is one who does have access to "the true being of each thing" (tou ontos hekastou) by which he would have a knowledge of the "pattern" (paradeigma) of things. This means, in other words, that the non-philosopher does not have "the absolute truth" (to alêthestaton), insofar as he restricts his knowing to the senisble world (484c).

After describing by means of a parable how the philosopher should have control over the affairs of state, Socrates describes the philosopher as one who, as a "true lover of knowledge" (philomathês), always strives to know "the true nature of every essence" (to on), not being content with the multiplicity of individual things. What is meant is that the philosopher seeks the absolutes, the Ideas, in which individual things called by the name of that absolute participates (490b). Socrates then explains that the true philosopher is one whose mind is fixed upon "true being" (alêthôs pros tois ousi) and whose "eye" is directed towards the fixed and immutable order (all' eis tetagmena atta kai kata tauta aei echonta horôntas), by which is meant the system of Ideas; in this way the philosopher "holding converse with the divine order (theioi dê kai kosmioi), becomes orderly and divine, as far as the nature of man allows" (500 c-d). When compelled to take control of the state, the philosopher will fashion a constitution that is an expression of "justice by nature" (or absolute justice) and beauty (by nature) and temperance (by nature) and so forth (to phusei dikaion--kai kalon kai sôphron kai panta ta toiauta). For this reason the philosopher is called a lover "of truth and being" (tou ontos te kai alêtheias).

    Those with an inborn capacity for philosophy should be nurtured in their philosophical development, in order that they may be fit to take power. Socrates contrasts this ideal education with what the Sophists provide the young; the differences are fundamental and presuppositional. Socrates criticizes the Sophists for equating knowledge with popular opinion; in other words, the Sophists wrongly espouse a form of relativism, equating reality with what the majority say of it. The task of the Sophist educator is to train the young to know popular opinion, in order to operate effectively in that social context. 

     Later in the chapter, somewhat unexpectedly, Socrates asserts that those philosophers in training to be rulers must reach the highest knowledge of all, which is the knowledge of "the Good" (to agathon). Glaucon then asks Socrates about the Good. (For the sake of orderliness of presentation, it is preferable to postpone a discussion of the Good until later.) This discussion leads eventually to Socrates's attempt to classify the types of cognitional activity and their corresponding subject matters or objects; these are set in a hierarchy that reflects the degree of truth and reality of the corresponding subject matters or objects and therefore the relative importance of the cognitional activities. The assumption is that something is more true and real insofar as it is ontologically more original; ontological originality is the attribute of having priority with respect to Being; to be ontologically original or prior is to be the cause or basis of other things, their principle or cause. Plato divides all cognitional activity into two types: section BC represents the intelligible whereas AB represents the visible. These two types are then each subdivided again into two types (AD, DB, BE and EC). It seems that the major division among the objects of cognitional activity is between knowledge (epistomê) and opinion (doxa), a distinction already introduced in Book Five. The objects of knowledge are the principles of mathematics and the Ideas, whereas the objects of opinion are the objects of the material world and representations of these.

     Eikasia (Representation) is the cognitive activity of perceiving sensible representations of perceptual objects; this is the lowest level of cognitional functioning, so that its objects have the least reality.  Pistis (Opinion) is the cognitive activity of perceiving by means of one or more of the five senses; the objects corresponding to pistis are perceptual objects, i.e., material objects susceptible of being perceived by means of one or more of the five senses. Perceptual objects have greater reality than images of reflections, because the latter are derivative of the former in their being. One then moves above the line into the level of the intelligible. Dianoia (reasoning) is the cognitive activity of reasoning from first principles (i.e., axioms) to mathematical truths. What Plato calls noêsis (knowledge), on the other hand, is the understanding of Ideas or Absolutes by means of dialectic. These are the most true and real of all objects of cognitive activity. Ideas are essences or definitions—pure concepts—in which individual material things participate and become what they are. They are eternal, immaterial conceptual realities that provide the means by which visible things are classified. Socrates explains that whenever there are many instances of something, such as the beautiful or the good, there must also be an idea under which the many instances are brought (507b). It must stressed again that for Plato the Ideas have objective reference; this means that they do not simply exist in the mind but that they really exist apart from their being thought and apart from their presence in the visible world. It is only by means of the Ideas that one can have opinions of the visible world at all, because without them one could not identify anything as something, i.e., as an instance of a universal. (Republic 510d - 511d)

    According to Plato, there is something more real than the Ideas or the things themselves (absolutes), which now necessitates a return to the question of the Good. All souls instinctively and intuitively seek the Good, but more often than not do not truly comprehend the Good (505e). Yet no one can be satisfied with the appearance (to dokounta) of the Good in the sensible or visible world but seek the reality (ta onta) of the Good (505d-e). Socrates says that "the Idea of the Good" (hê tou agathou idea) is the greatest object of study, so that one Idea is elevated above the others (505a). He insists, however, that the Good can only partially be known; for this reason, he refuses to talk about the Good, but prefers to talk about the child of the Good, the sun. Socrates begins by describing sight as being in the eyes; unlike the other sense organs, in order for it to operate, the eye, in which sight resides, needs not only a visual object but also light. Light is the condition for the eye to see. To say that the sun is the child of the Good is to say that the sun functions in the visible world analogously to the way that the Good functions in the intelligible world, the realm of Ideas. (Remember that in the ancient world the sun is the only true source of light.) (The metaphor of the sun tends to be used rather flexibly, as will become apparent.) The Good is the condition for the eyes of the soul to know its objects, the Ideas; the Good is not the eyes of the soul, in the same way as the sun is not the eye in which sight resides. Socrates says, "And the soul is like the eye: when resting upon that on which truth and being shine, the soul perceives and understands and is radiant with intelligence" (508d).

    Socrates then elaborates further on the parallelism between the sun and the Good:

Now, that which imparts truth to the known and the power of knowing to the knower is what I would have you term the Idea of Good, and this you will deem to be the cause of knowledge, and of truth in so far as the latter becomes the object of knowledge...and, as in the previous instance, light and sight may be truly said to be like the sun, and yet not to be the sun, so in this other sphere, knowledge and truth may be deemed to be like the Good, but not the Good; the Good has a place of honour yet higher. (508e-509a)

The sun makes possible light and sight, but is not to be identified with either one. Similarly, the Good makes possible knowledge and truth, which correspond to sight (= knowledge) and light (= truth) in the intellectual world. In other words, the Good gives truth (tên aleitheia) to the objects of knowledge and gives power to know (tôi gignôskonti tên dunamin) to the mind. To say that the Good gives the power to know to the mind is to say that the Good is manifested as consciousness, which is what is meant by knowledge. To say that the Good gives truth to the objects of knowledge is to say that the Good is the source of all the Ideas, which is what is meant by truth. And insofar as the Ideas are the source of all visible things, as that which makes them what they are, i.e., gives them intelligibility, the Good is the source of the visible world as well. In other words, the Good has ontological originality, being the first principle of all things. Thus, the Good is both absolute subject and object, the self-same principle of being and of knowing. Since the Good is the source of knowledge and truth knowledge and truth are Good-like, but are not the Good. It is also said that the Good is the beautiful insofar as knowledge and truth are beautiful, but exceeds the latter in beauty (508e).

    Further along the lines of the Good as the source of truth, Socrates points out that, like the sun, the Good "may be said to be not only the author of knowledge to all things known, but of their being and essence (kai to einai te kai tên ousian)." What is meant is that the Good is the cause of the very existence of the Ideas and all sensible objects that participate in the Ideas. Yet, he cautions that the Good cannot be said to be the same as those things that are caused to be by the Good: "And yet the Good is not essence (ousia), but far exceeds essence in dignity and power" (509b). For Plato, the Good transcends essence, which means that it transcends the Ideas, which are the essences of all visible things. Thus, the Idea of the Good is not like the other Ideas; one can now understand why Socrates is reluctant to talk about the Good: one cannot talk about what is beyond essence.

2.3.3. Republic 7

In this chapter is found Plato's famous cave-metaphor; its purpose is to depict the ascent of the soul to the level of noêsis. The natural state of a human being is to be as if in a cave with his face permanently pointed towards the inside wall of the cave; between the people and the mouth of the cave there is a fire and between the fire and the people there is something like a screen. Behind the screen people walk carrying statutes of animals and human beings so that they cast shadows upon the inside wall of the cave. A person who has from childhood only seen these images and nothing else will naturally assume that these images are real, indeed the only real. This represents the level of eikasia.  If one broke free and looked at the statues causing the images, one would see that which has been causing the shadows.  This represents the movement to the level of pistis. Imagine then that the same person next ventured outside the cave and saw the objects of the world as illumined by the sun; this corresponds to the level of understanding wherein a person knows the Ideas (noêsis). Finally,  if he looked up at the sun, the same person would see that which causes one to see anything at all. This represents knowledge of the Good.  If this now-enlightened person went back into the cave and tried to convince his fellow-prisoners of what he had seen, he would scarcely be believed; thus his task would be the educate his fellow prisoners so that they can eventually come to understand.

    In Republic 517 b-c, part of the cave metaphor,  Plato makes two important points. First he speaks of "the ascent of the soul into the intellectual world" (tôn anô tên eis ton noêton topon tês psuchês anodon). Coming out of the cave into the light of day represents the soul's ascent through the levels of cognition to the level of knowledge ("the intellectual world") terminating in the contemplation of the Idea of the Good. Second, Socrates says of the Idea of the Good that it is "the cause for all things of all that is right and beautiful (orthôn te kai kalôn), giving birth in the visible world to light, and the author of light and itself in the intelligible world being the authentic source of truth and reason, and that anyone who is to act wisely in private or public must have caught sight of this" (517c). The Good is the cause in the visible world of light and the source of light (sun); in the intelligible world, the Good is the cause of knowledge and truth. Thus, it would seem that Plato thought that there was more than simply an analogy between the sun and the Good: the sun is the actual manifestation of the Good in the material world in addition to being analogous to it in its function. (Republic 514a - 517c)

2 .4. Important References to Plato's Teaching About Ideas in Aristotle's Works

2.4.1.  Eudemian Ethics

For it is said that the best of all things is the Good Itself, and that the Good Itself is that which has the attributes of being the first of goods and of being by its presence the cause to the other goods of their being good; and both of these attributes, it is said, belong to the Idea of Good (I mean both being the first of goods and being by its presence the cause to the other goods of their being good), since it is of that Idea that Goodness is most truly predicated (inasmuch as the other goods are good by participation in and resemblance to the Idea of Good) and also it is the first of goods, for the destruction of that which is participated in involves the destruction of the things participating in the Idea (which get their designation by participating in it), and that is the relation existing between what is primary and what is subsequent; so that the Idea of Good is the Good Itself, inasmuch as the Idea of Good is separable from the things that participate in it, as are the other Ideas also. (1217b)

In Eudemian Ethics 1217b, Aristotle provides a summary of Plato's doctrine of the Idea of the Good. The highest of all things is the Good Itself, the presence of which is the reason that anything else is good. The Idea of the Good is separable from the things that participate in it. In further discussing Plato's doctrine of the Good, Aristotle also reveals that Plato and his school hold that the Good is also the One (or Unity): "On the assumption that Goodness is a property of numbers and monads because the Good Itself is the One (to hen)" (1218a).

2.4.2. Metaphysics

After the systems we have named came the philosophy of Plato, which in most respects followed these thinkers, but had pecularities that distinguished it from the philosophy of the Italians. For, having in his youth first become familiar with Cratylus and with the Heraclitean doctrines (that all sensible things are ever in a state of flux and there is no knowledge about them), these views he held even in later years. Socrates, however, was busying himself about ethical matters and neglecting the world of nature as a whole but seeking the universal in these ethical matters, and fixed thought for the first time on definitions; Plato accepted his teaching, but held that the problem applied not to sensible things but to entities of another kind-for this reason, that the common definition could not be a definition of any sensible thing, as they were always changing. Things of this other sort, then, he called Ideas (ideas), and sensible things, he said, were all named after these, and in virtue of a relation to these; for the many existed by participation in the Ideas (eidesin) that have the same name as they. Only the name 'participation' was new; for the Pythagoreans say that things exist by 'imitation' of numbers, and Plato says they exist by participation, changing the name. But what the participation or the imitation of the ideas (tôn eidôn) could be they left an open question.  Further, besides sensible things and Ideas (tôn eidôn) he says there are the objects of mathematics, which occupy an intermediate position, differing from sensible things in being eternal and unchangeable, from ideas in that there are many alike, while the Idea itself (eidon auto) is in each case unique.   Since the Ideas (ta eidê) were the causes of all other things, he thought their elements (stoicheia) were the elements of all things. As matter (hulê), the great and the small were principles (archas); as essence (ousia), the One (to hen); for from the great and the small, by participation in the One, come the Numbers.  But he agreed with the Pythagoreans in saying that the One is essence (ousia) and not a predicate of something else; and in saying that the Numbers are the causes of the essence (ousia) of other things he agreed with them; but positing a dyad and constructing the infinite out of great and small, instead of treating the infinite as one, is peculiar to him; and so is his view that the Numbers exist apart from sensible things, while they say that the things themselves are Numbers, and do not posit an intermediate class of objects of mathematics. His divergence from the Pythagoreans in making the One and the Numbers separate from things, and his introduction of the Ideas (tôn eidôn), were due to his inquiries in the region of definitions (for the earlier thinkers had no tincture of dialectic), and his making the other entity besides the One a dyad was due to the belief that the numbers, except those which were prime, could be neatly produced out of the dyad as out of some plastic material. Yet what happens is the contrary; the theory is not a reasonable one. For they make many things out of the matter, and the Idea (to eidos) generates only once, but what we observe is that one table is made from one matter, while the man who applies the Idea (to eidos), though he is one, makes many tables. And the relation of the male to the female is similar; for the latter is impregnated by one copulation, but the male impregnates many females; yet these are analogues of those first principles.   Plato, then, declared himself thus on the points in question; it is evident from what has been said that he has used only two causes, that of the essence (ti estin) and the material cause (tê hulên) or the Ideas (tois eidesi) are the causes of the essence of all other things, and the One (to hen) is the cause of the essence of the Ideas); and it is evident what the underlying matter is, of which the ideas are predicated in the case of sensible things, and the One in the case of Ideas, viz. that this is a dyad, the great and the small. Further, he has assigned the cause of good (eu) and that of evil to the elements, one to each of the two, as we say some of his predecessors sought to do, e.g. Empedocles and Anaxagoras.

In Metaphysics 1.6, Aristotle explains that Plato taught that the Ideas (ta eidê) were the cause of all things and that the One (to hen) (which Aristotle says elsewhere is identical to the Good), is the cause of the Ideas. He writes, "Plato, then, declared himself thus on the points in question; it is evident from what has been said that he has used only two causes, that of the essence (ti estin) and the material cause (tê hulên) or the ideas (tois eidesi) are the causes of the essence of all other things, and the One (to hen) is the cause of the essence of the ideas." (Why Aristotle uses the terms idea and eidon is not at all clear, but they seem to be used synonyms.) Aristotle adds that Plato, "agreed with the Pythagoreans in saying that the One is essence (ousia) and not a predicate of something else." This seems to mean that Plato viewed the One as the source of all things so that it is not a predicate of anything but everything is predicated of it in the sense that everything ultimately is a manifestation of the One as essence.

    Aristotle gives evidence that Plato had incorporated some Pythagorean elements into his philosophy, which are mostly absent from his dialogues. It is possible that these represented an esoteric teaching addressed only to the initiates of his school. Although it is difficult to reconstruct Plato's views owing to the brevity of Aristotle's account, it seems that Plato's One (to hen) is synonymous with the Pythagorean Monad. From the One comes numbers by the participation of the great and the small in the One. It seems that Plato distinguished numbers from Ideas and prime matter ("the great and the small") respectively; they occupied an intermediate place between the two. There are many numbers insofar as there are many material objects that can be numbered; in other words, there is a number for each numerable thing. But the Idea of the number apart from the sensible world is one, not many, because all numbers are composed of ones (or units). This seems to be what Aristotle means when he says "for from the great and the small, by participation in the One, come the Numbers." Moreover, according to Aristotle, Plato followed the Pythagoreans in identifying Ideas with numbers: "The Numbers are the causes of the essence (ousia) of other things." For Plato all things were numbers insofar as numbers were intermediate exemplications of the Ideas. This aspect of Plato's thought, however, tends to be obscure, for it is unclear why numbers are Ideas when numbers seem to result from exemplications of Ideas in matter. Plato's concept of "the great and the small" (to mega kai to mikron) seems to be the Pythagorean unlimited/even, which is indeterminate and passive prime matter. It is possible that Plato called it "the great and the small" because it is both great and small and neither great nor small insofar as it is indeterminate. Aristotle adds that Plato posits "a dyad" and constructs "the infinite out of great and small." In Pythagoreanism, the dyad is another term used to denote the material principle, and is said to be identical to the unlimited or infinite. It seems that for Plato the great and the small is the dyad, the infinite or formless material principle. Aristotle enumerates more similarities and differences between Plato and the Pythagoreans, which are difficult to understand (see also Metaphysics 1.9; 988a 10-11; Books 13, 14; Physics 1.9).
 

3. Cosmology in Timaeus

Although in all of his dialogues he touches upon cosmology, Timaeus is Plato's explicit attempt to to present his understanding of the origin and nature of the cosmos; it was very influential in the ancient world and remained so well beyond that time period. After relating a story about the ancient Athenians and the island of Atlantis, Timaeus takes up the task of explaining the origin and nature of the universe, by which he means the totality of created and corporeal existence.

3 .1. The Probability of the Account of the Origin and Nature of the Cosmos

Timaeus, who, in the dialogue, represents Plato's views, says that, in setting forth his cosmology, he is operating in the realm of the probable only (Timaeus 29b-d). Plato believes that one can only speak truly of  the changeless and intelligible realm, "the eternal things themselves." The reason for this is that only with respect to the eternal, the originals that are used as prototypes of things in the realm of becoming, words are used univocally: they correspond exactly to the unchanging realities to which they refer. When used to point to things in the realm of becoming, however, words used originally and primarily of the eternal things can have only an analogous sense.  For example, the experience of a beautiful flower is analogous to Beauty Itself or Absolute Beauty. The realm of becoming is partially the realm of the unintelligible; it is the distinction made between knowledge and opinion set forth in Republic 5. Thus, since he is dealing with the realm of becoming, Timaeus says that his hearers must be content with opinion and probability, since words used originally and primarily of the eternal things only partially apply to things that are becoming. For this reason, they are not to be surprised to discover that the account has inconsistencies. Timaeus reiterates that his account is only probable, and cautions his hearers that he is not to be taken as making dogmatic pronouncements (see Timaeus 48 c-e). Later in the dialogue, he again contrasts the "meditations about eternal things" with a consideration of the "truths of generation which are probable only."  (Timaeus 59 c-d)  The pursuit of the former is, naturally, more important, but the occasional inquiry into the latter does provide a pleasurable diversion, even if one cannot attain to certainty.

3.2. The Destruction of Atlantis and the Original Athenians

The dialogue begins with the report from Critias that, when he was ten years old, he heard a elderly man tell a story about Solon's conversations with an Egyptian priest; the priest said that Athens once led a united Mediterranean defense against invaders from Atlantis, defeating them. Afterwards, a flood and an earthquake destroyed both the Athenians and the whole island of Atlantis; the Egyptians survived and kept records of these events, whereas a new generation of Athenians emerged with no remembrance of their past and their relation with other peoples. This, by the way, gives us a perspective on how some Greeks understood themselves in relation to other, more ancient cultures; there seems to have some embarrassment on the part of the Greeks for not being known as an ancient people. (Timaeus 20d-27b)

3 .3. Necessity of a Creator

Timaeus sets out the well-known Platonic distinction between the realm of the incorporeal, the eternal and being, which is apprehended by intelligence and  reason and that of the corporeal, the temporal and becoming, which is apprehended by opinion or sense perception. It is the distinction between, "What is that which always is and has no becoming; and what is that which is always becoming and never is" (27d). He further asserts that whatever is becoming must come into existence by some cause; the cosmos, therefore, since it is becoming, needs a creator. He writes, "All sensible things are apprehended by opinion and sense and are in a process of creation and created. Now that which is created must, as we affirm, of necessity be created by a cause" (23 b-c). The realm of becoming is neither eternal nor self-caused, but was brought into being by the creator (dêmiourgos), the father of all; Timaeus cautions, however, that the creator is inscrutable:  "But the father and maker (poiêtês) of all is past finding out, and even if we found him, to tell of him to men would be impossible" (28c). Because he is good, the creator made the cosmos after the pattern of the unchangeable and eternal: "The world has been framed in the likeness of that which is apprehended by reason and mind and is unchangeable" (29a); thus the cosmos is a copy of the eternal and unchanging. (As will become clear, God did not create the universe ex nihilo.)  (Timaeus 27d-29c)
 

3.4. The Process of Creation

According to Plato, God, the creator, took over that which was moving in irregular and disorderly fashion, and imposed on it regularity and order; this was done, as already indicated, by using the eternal things, the Ideas, as templates. He describes this process as the putting of a soul into the body of the universe, thereby putting intelligence (regularity and order)  into it. (Timaeus 29e-30c). Into the center of the body of the universe, which is a sphere, God placed the soul, which is then diffused through the entire body and even envelopes it; the soul is to rule the body. This being is called a "blessed god." Timaeus describes the world soul as a third type of being created from "the being which is indivisible and unchangeable and from that kind of being which is distributed among bodies" (35a). He explains the process whereby the soul was created as follows:

"And he made her out of the following elements and in this way: Out of the indivisible and unchangeable, and also out of that which is divisible and has to do with material bodies, he compounded a third and intermediate kind of being, partaking of the nature of the same and of the other, and this compound he placed accordingly in a mean between the indivisible, and the divisible and material. He took the three elements of the same, the other, and the being, and mingled them into one Idea (eidos), compressing by force the reluctant and unsociable nature of the other into the same" (34c-35a).

In other words, the world soul is the combination of intermediate being with intermediate sameness and intermediate otherness or difference to form a composite; since the soul is composed not only of intermediate being, but also intermediate sameness and otherness or difference it can recognize sameness and otherness or difference in being in the world of generation and the world of eternal being as it encounters them. The world-soul is also said to be invisible, partaking of reason and harmony, and to be the best thing created. It is self-moving and turns in revolutions upon itself.
 

3.5. The Cosmos as a Moving Image of Eternity

The creator desired to make the copy, the universe, as much like the original, the Ideas, as possible. Since the latter is eternal, he attempted to make the former as eternal as possible.  Unfortunately, since the universe is not everlasting, the creator could only make the universe "a moving image of eternity." This means that he made part of the universe, the sphere of the heavens, move in predictable rotations, "moving according to number." It seems that, for Plato, time is the movement of the sphere of heaven; time comes into existence with motion or change. Circular motion stands closest to motionless eternity, because no permanent locomotion occurs, since that which is moving in a circle always returns to where it started. By the movement of the spheres, the becoming of the universe is measured, i.e., days, months, years etc. (Timaeus 37c - 38c)

3 .6. The Cosmos as a All-Inclusive Creature

Timaeus explains that God made the cosmos after the likeness of a living being that includes all other living beings: "The heavenly race of the gods; another, the race of birds whose way is in the air; the third, the watery species; and the fourth, the pedestrian and land creatures."  In other words, God created the cosmos after the Idea that includes all types of living beings. Since there is only one such Idea, there is only one cosmos. Because the cosmos is a copy of the one absolute Living Creature, the Ideas of all other creatures are to be found within it. The one universe is actually all beings at once.  (Timaeus 30c - 31b; 39e - 40a)

3 .7.  The Third Type of Being

Timaeus says that there is another type of being than the indestructible and invisible Ideas and those things that perceptible objects that bear the names of the Ideas. This third type of being is unformed matter existing in space.  He calls this third thing, "the receptacle" and the "nurse of all becoming" (49b), and distinguishes this from "a pattern intelligible and always the same" and that which "was only an imitation of the pattern, generated and visible" (49a). Expressed differently, this third thing is a receiving principle that receives the Ideas and produces thereby an object of perception: "And we may liken the receiving principle to a mother, and the source or spring to a father, and the intermediate nature to a child." Although Timaeus calls this third thing "space," he does not mean that it empty space, but space filled with formless matter. This third thing is indestructible and eternal. Thus, it is this third thing that the creator took over and infused with soul and intelligence.  (Timaeus 48e - 52c)
 

3.8.  Triangles

Within the formless matter of the receptacle, two types of triangles arise; these are the isosceles, which has only one form, and one particular type of the scalene triangle. The triangle is the first two-dimensional figure that can be created from points. These triangles combine in various ways to produce the four elements: earth, water, air and fire. The two-dimensional triangles become the three-dimensional elements. The elements, participating in the other Ideas, become all corporeal things. (Timaeus 53c - 55d)

3.9.  The Human Being

In Timaeus, the human being is one of the three classes of mortal beings created partially by the gods (which were created by the dêmiourgos and are visible—the stars and planets—and invisible) and partially by the dêmiourgos. The body, which is mortal, was created by the gods (cf. 42e-43a), whereas the soul was placed in the body directly by God; the soul is called the guiding principle and the divine part (41b-d). Individual souls are made out of the same stuff as the world soul, although it is explained that this stuff was not as pure as before (41d). Each soul was assigned a star (41d); if a person lived well, upon the death of the body the soul would return and dwell in his home star; if not, then the soul would be reincarnated (42a-c). Later in Timaeus, it is said that a human being has two souls, one immortal, created by the creator and one mortal, created by the gods, the offspring of the creator; the latter is subject to "terrible and irresistible affections" (69c). The mortal soul is placed in the breast and thorax, while the immortal soul inhabits the head. The mortal and inferior soul is subdivided into two parts occupying different parts of the body: "That part of the inferior soul which is endowed with courage and passion and loves contention, they placed nearer the head, midway between the midriff and the neck" (70a). This part of the mortal soul is allied with the immortal soul, which is to direct the other part of the inferior soul, the appetites, in check. (A similar statement of the tripartite view of the soul is found in Republic 4.)
 

Questions for Discussion

1. Is it true that for there to be beautiful things there must exist beauty itself? If you do not agree, how do you account for the existence of abstractions?

2. Are Ideas the causes of individual material things?

3. On the assumption of the validity of Plato's doctrine of Ideas, does it follow that there must be the Idea of the Good or the One?

4. Do you find the argument convincing that we know the Good Itself exists because we all seek the good in all that we do?

5. Why is it that Plato says that the Good is not essence (ousia), but far exceeds essence in dignity and power?

6. What is the Being Itself or "truly existing existence" of which Plato speaks in Phaedrus? Is it to be identified with the Good and the One? Why does it have no qualities?

7. Does the universe require a creator as Plato argues in the Timaeus?

8. Why does Plato say that the creator is past finding out, and even if we found him, to tell of him to men would be impossible?

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