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History of Philosophy
Plato
by Turner, William (S.T.D.)

Life. Plato was born at Athens some years after the beginning of the Peloponnesian War. The exact year of his birth is unknown, but 427 or 428 B.C. is the most probable date. His father's name was Aristo; his mother, Perictione, was descended from Dropides, a near relative of Solon. Plato was originally called Aristocles, Platôn being a nickname given by his master in gymnastics on account of his broad build.

Concerning his early life we do not possess much reliable information. We may, however, presume that he profited by all the educational advantages that were within the reach of a noble and wealthy Athenian youth. Zeller^[1] calls attention to three circumstances which had a determining influence on the development of Plato's mind. The first of these was the political condition of Athens. The city was just then experiencing the full effects of demagogic rule, and the conditions at home and abroad were such that the mind of the aristocratic young student naturally turned towards idealistic schemes of state organization, schemes which were later to find expression in The Republic. The second circumstance is the fact that in early life Plato devoted much attention to poetry, composing poems of no mean artistic value. These early studies were not without effect on his philosophy; they influenced the entire spirit of his system as well as the language, so remarkable for its grace and beauty, in which that system was set forth. Indeed, it is true, in a sense, that Plato became a philosopher without ceasing to be a poet. The circumstance, however, which was most decisive in determining the life and philosophy of Plato was the personal influence of Socrates; for though he had studied the doctrines of Heraclitus under Cratylus, his philosophical training may be said to date from his first meeting with Socrates.

[1] Plato, etc., pp. 7 ff

After the death of Socrates, Plato, who had spent about eight years as disciple, began his travels preparatory to establishing a school of his own. He first repaired to Megara,^[2] where some of the disciples of Socrates were gathered under the leadership of Euclid. Thence he went to Italy to obtain a more intimate acquaintance with the doctrines of the Pythagoreans. The exact order of his subsequent journeys is not certain still, there is no reason to doubt that he visited Egypt, although the tales that are told of the vast stores of learning which he acquired in that country are far from reliable. We may accept as true the story of his journeys to Sicily, and of his relations with the elder Dionysius, who sold him into slavery, as well as with Dionysius the younger, whom he tried to convert to his Utopian scheme of state government.

[2] Some historians doubt the accuracy of this statement, which rests on the authority of Hermodorus, a disciple of Plato. cf. Zeller, op. cit., p. 14, note 26.

It was after his first journey to Sicily that Plato began his career at Athens as a teacher. Imitating his master, Socrates, he gathered round him the young men of the city, but, unlike Socrates, he refused to teach in the public squares, preferring the retirement of the groves near the gymnasium of Academus. There he met his disciples, conversing with them after the manner of Socrates, though it is natural to suppose that in his style as well as in his choice of illustrations he departed from the Socratic example of studied plainness. On his return from his third journey to Sicily, Plato took up his residence permanently in Athens, and thenceforth devoted himself unremittingly to teaching and writing. He lived to the age of eighty, dying in the midst of his intellectual labors. If Cicero's story be true,^[3] he died in the act of writing; according to another tradition prevalent in ancient times, he died at a wedding feast.

[3] Cf. Cicero, De Senectute, V, 13.

Plato's Character. Even in antiquity, the character of Plato was violently assailed. His dealings with Socrates and afterwards with his own disciples, his visits to Sicily, his references to the philosophical systems of his predecessors, were all made the pretext for accusations of self-assertion, tyranny, flattery of tyrants, plagiarism, and willful misrepresentation. His aristocratic ways and his disdain of the ostentatious asceticism of the Cynics served as the basis for charges of love of pleasure and immorality. The evidence on which all these accusations rests is of the flimsiest nature, while, on the contrary, everything that Plato wrote bears testimony to the lofty nobility of the man. The truth is that Plato's character was not easily understood. When the idealism and poetic temperament which were his by instinct and early training broke loose from the restraint of Socratic influence, he was merely realizing in his personal character the ideal of Greek life -- an ideal which, by reason of its many-sidedness, was a contradiction and a scandal to the narrow-minded advocates of asceticism and abstemiousness. The importance which Plato attached to a larger culture was taken by the Cynics and his other adversaries as a sign that he had abandoned, whereas he was in reality but rounding out and perfecting, the Socratic idea of what a philosopher ought to be.

Plato's Writings.^[4] We are fortunate in possessing all the genuine works of Plato. The so-called Platonic dialogues which are spoken of as lost are certainly spurious. The Divisions mentioned by Aristotle is neither a Platonic nor an Aristotelian treatise; the agrapha dogmata, of which Aristotle also makes mention, is most likely a collection of the views which Plato himsell had not committed to writing, but which some disciple collected for the use of the school.

[4] Cf. Ueberweg, History of Philosophy, English trans., pp. 108 ff.

While nothing that Plato wrote has been lost, it is by no means easy to determine how many of the thirty-six dialogues that have come down to us are undoubtedly authentic. With respect to Phaedrus, Protagoras, The Banquet, Gorgias, The Republic, Timaeus, Thaetetus, and Phaedo , there can be no reasonable doubt. Others, like Parmenides, Cratylus, The Sophist, are not so certainly genuine; while in the case of Minos, Hipparchus, etc., the balance of evidence is against their authenticity.^[5]

[5] The paging employed in citations from Plato's Works is that of the Stephanus edition (Paris, 1578). This paging is preserved in the more recent editions, for example, Bekker's (Berlin, 1816-1823), Didot's (Paris, 1846 ff.), and also in Jowett's translation (The Dialogues of Plato, Oxford, 1871; third edition, New York and London, 1892). For general bibliography, cf. Weber, op. cit., p. 77, n.; Ueberweg, op. cit., p. x7; to these lists add Ritchie, Plato (New York, 1902).

Next comes the question of the order or plan of the Platonic dialogues. Ueberweg mentions the three principal theories held by scholars. They are (1) that Plato wrote according to a definite plan, composing first the elementary dialogues, then the mediatory, and finally the constructive discourses; (2) that he had no definite plan, but that the dialogues represent the different stages in the development of his mind; (3) that he deliberately portrayed in his dialogues the several stages in the life of Socrates, the ideal philosopher. Zeller, however, very sensibly remarks^[6] that the question has been argued too much on a priori grounds, and suggests that the first thing to do is to determine the order in which the dialogues were written -- a task that is by no means easy.

[6] Plato, pp. 118 ff.

The form of the Platonic writings is, as is well known, the dialogue; the reasons why Plato adopted this literary form are not far to seek. In the first place, he was influenced by the Socratic method; secondly, he was poet enough to recognize the dramatic effect of which the dialogue is capable, and the room which it affords for local coloring and portrayal of character. Finally, he must have recognized that the dialogue afforded him the amplest opportunity of presenting the life of the model philosopher in the words and acts of the idealized Socrates. Philosophy was for Plato a matter of life as well as of thought; "true philosophy, therefore, could only be represented in the perfect philosopher, in the personality, words, and demeanor of Socrates."

The Platonic dialogue has been well described as occupying a middle position between the personal converse of Socrates and the purely scientific continuous exposition of Aristotle.^[7] Plato, adopting a stricter idea of method than Socrates adopted, excludes the personal and contingent elements which made the discourse of Socrates so picturesque; while at times, when he explains the more difficult points of doctrine, he abandons almost altogether the inductive method for the deductive, the dialogue well-nigh disappears and gives way to unbroken discourse. This is especially true of the Timaeus.

[7] Cf. Zeller, op. cit., p. 153.

In his use of the dialogue, Plato constantly has recourse to the myth as a form of expression. The poetical and artistic value of the myth is conceded by all, but it offers no small difficulty when there is question of the philosophical doctrine which it was meant to convey. Whatever may have been Plato's purpose in introducing the myth, -- whether it was to elucidate by concrete imagery some abstract principle, or to mislead the unthinking populace as to his religious convictions, or to conceal the contradictions of his thought, striving to "escape philosophical criticism by seeking refuge in the license of the poet," -- there can be no doubt that the myth was intended to be a mere allegory, and Plato himself warns us against taking such allegories for truth, the shadow for the substance.

PLATO'S PHILOSOPHY

Definition of Philosophy. Plato's philosophy is essentially a completion and extension of the philosophy of Socrates. What Socrates laid down as a principle of knowledge, Plato enunciates as a principle of Being; the Socratic concept, which was epistemological, is succeeded by the Platonic Idea, which is a metaphysical notion. Socrates taught that knowledge through concepts is the only true knowledge; therefore, concludes Plato, the concept, or the Idea, is the only true reality. Thus, for Plato, philosophy is the science of the Idea, or, as we should say, of the unconditioned basis of phenomena.

In the Phaedrus^[8] Plato describes how the soul, at sight of singular phenomena, is moved to a remembrance of its heavenly home and of the archetypes which it contemplated in a previous existence, and of which it now beholds the imperfect copies. Thereupon, the soul, falling into an ecstasy of delight, wonders at the contrast between the Idea (archetype) and the phenomenon (copy), and from this wonder proceeds the impulse to philosophize, which is identical with the impulse to love. For, while it is true that there is a contrast between every Idea and its phenomenon, the contrast is more striking in the case of the Idea of the beautiful, this Idea shining through its visible copies more perfectly than any other Idea. Philosophy, then, is the effort of the human mind to rise from the contemplation of visible copies of Ideas to the knowledge of Ideas themselves.

[8] Phaedrus, 250.

To the question, How is this knowledge of Ideas to be attained? Plato answers, By means of dialectic -- to this all other training is preliminary. Plato, moreover, is careful to distinguish between knowledge (epistêmê) and opinion (doxa), -- so that, when he defines philosophy as knowledge, we must understand him to speak of knowledge in the stricter sense of the term.^[9]

[9] Cf. Gorgias, 454 D; Meno, 97 E.

Division of Plato's Philosophy. Plato, unlike Aristotle, neither distinguished between the different parts of philosophy, nor made each part the subject of a separate treatise. Still, the doctrines found in the dialogues may be classed under the three heads of Dialectic, Physics, and Ethics -- a division which, according to Cicero, was made by Plato himself, although it is more probable that it was first formulated by Xenocrates, as Sextus^[10] says. Under the title Dialectic it is customary to include not only logic, but also the doctrine of Ideas. Under the division Physics are comprised Plato's doctrine concerning the world of phenomena in general, his teaching regarding the relation between Idea and phenomenon, his cosmogenetic theories, his notions of matter, space, and so forth. Finally, under Ethics are included not only questions which belong to the science of morals, but also the political doctrines which play so important a part in the Platonic system.

[10] Mathem., VII, 16.

Dialectic.^[11] It would be idle to look to Plato for a system of logic. We find, indeed, that he mentions certain laws of thought, but he enunciates them as laws of being, making them serve a metaphysical rather than a logical purpose.^[12] It is owing, perhaps, to this tendency of Plato's mind towards the metaphysical view that definition and division receive more of his attention than do the other problems of logic; dialectic, he teaches, is concerned (as is every part of philosophy) with the Idea, or, more explicitly, dialectic has for its object to reduce what is manifold and multiple in our experience of phenomena to that unity of concept which belongs to a knowledge of Ideas, and, furthermore, to establish an organic order among the concepts thus acquired. Dialectic has, therefore, the double task of defining universal concepts by induction (sunagôgê) and classifying them by division (diairesis).^[13]

[11] Cf. Lutoslawski, Origin and Growth of Plato's Logic, etc. (London, 1897).

[12] Cf. Phaedo, 100 A; Tim., 28 A.

[13] Cf. Phaedrus, 265 E.

Definition and division together with some remarks on the problem of language are the only logical doctrines to be found in the dialogues. Dialectic, however, includes, besides logical doctrines, the theory of Ideas, which is the center of all Platonic thought; for dialectic is the doctrine of the Idea in itself, just as physics is the doctrine of the Idea imitated in nature, or as ethics is the doctrine of the Idea imitated in human action. Under the title of Dialectic, therefore, the theory of Ideas is studied; it includes the following questions: (1) origin of the theory of Ideas; (2) nature and objective existence of the Ideas; (3) their expansion into plurality: formation of the world of Ideas.

1. Origin of the theory of Ideas. The theory of Ideas, as has been remarked above, is a natural development of the Socratic doctrine of concepts. Knowledge, as distinct from opinion, is the knowledge of reality. Now, Socrates taught that in order to know a thing it is necessary and sufficient to have a concept of that thing. Therefore, the concept, or Idea, is the only reality.^[14] To deny that the Idea is a reality is to deny the possibility of scientific knowledge.

[14] Cf. Tim., 51.

Such is the first and most immediate derivation of the theory of Ideas. Starting from Socratic premises, Plato argues that the theory of Ideas is the only explanation of the objective value of scientific knowledge. Elsewhere, however, as in the Philebus,^[15] he derives the doctrine of Ideas from the failure of Heraclitus and the Eleatics to explain Being and Becoming. Heraclitus was right in teaching that Becoming exists; he was wrong in teaching that Being does not exist. The Eleatics, on the contrary, were right in teaching that Being is, but they were wrong in teaching that Becoming is not. The truth is that both Being and Becoming exist. When, however, we come to analyze Becoming we find that it is made up of Being and not-Being. Consequently, in the changing world around us, that alone is real which is unchangeable, absolute, one, namely the Idea. For example, the concrete, changeable just is made up partly of what we would call the contingent element, the element of imperfection, of not-Being, and partly of the one immutable Idea, justice, which alone possesses real being. To say, then, that the Idea of justice does not exist is to say that the just (a just man or a just action) is all not-Being and has no reality. And what is said of justice may be said of any other Idea. The Idea is the core of reality underlying the surface qualities which are imperfections, i.e., unrealities.

[15] Phileb., 54 B.

Thus the reality of Being and the reality of scientific knowledge demand the existence of the Idea, and this double aspect of the Idea is never absent from Plato's thought: the Idea is a necessary postulate if we maintain, as we must maintain, the reality of scientific knowledge and the reality of Being. These are the two roads that lead to the Idea, -- the Socratic doctrine of concepts and the problem of Being and Becoming, a problem that was stated, though not satisfactorily solved, by Heraclitus and the Eleatics.^[16]

[16] Cf. Arist., Met., I, 6, 987 a, 29.

Besides these philosophical principles which led to the theory of Ideas, there existed in the mind of Plato what may be called a temperamental predisposition to adopt some such theory as the doctrine of Ideas and by means of it to explain knowledge and reality; for Plato was a poet and in him the artistic sense was always predominant. He was a Greek of the Greeks, and the Greek even in his mythology loved clearly cut, firmly outlined forms, definite, visible shapes. It was natural, therefore, for Plato not merely to distinguish in things the permanent element which is their Being and the object of our knowledge, but also to extract, as it were, this element from the manifold and changeable in which it was embedded, and to hypostatize it, causing it to stand out in a world of its own, in all its oneness and definiteness and immutability.

2. The nature and objective existence of the Ideas. From what has been said, it is clear that the Idea is the element of reality in things -- the one uniform, immutable element, unaffected by multiplicity, change, and partial not-Being. The expressions which Plato uses to describe the Idea always imply one or several of these attributes. For instance, he calls it ousia, aidios ousia, ontôs on, pantelôs on, kata tauta on, aei kata tauta echon akinêtôs, etc. The name, however, by which the Idea is most commonly designated is eidos, or idea, which primarily denotes something objective, though in a secondary sense the Platonic Idea is also an idea in our meaning of the word, a concept by which the object is known. But whether the Idea be considered subjectively or objectively, -- and the objective aspect is always to be considered first, -- it is essentially universal, or, to use Aristotle's phrase, hen epi pollôn. We may call it the universal essence if we are careful to dissociate from the word essence the meaning of something existing in things; for nothing is clearer than that Plato understood by the Idea something existing apart from (chôris) the phenomena which make up the world of sense. The Idea transcends the world of concrete existence; it abides in the heavenly sphere, the topos noetos, where the gods and the souls of the blessed contemplate it. It is described in the Phaedrus^[17] as follows: "Now of the heaven which is above the heavens no earthly poet has ever sung or ever will sing in a worthy manner. I must tell, for I am bound to speak truly when speaking of truth. The colorless and formless and intangible essence is visible to the mind, which is the only lord of the soul. Circling this in the region above the heavens is the place of true knowledge." In The Banquet^[18] the Idea of beauty is described "beauty only, absolute, separate, simple, and everlasting." There can be no doubt, therefore, that Plato separated the world of Ideas from the world of concrete existence. He hypostatized, so to speak, the Idea, and it was against this separation (chôrizein) of the Idea that Aristotle directed his criticism of Plato's theory. According to Aristotle, the Platonic world of Ideas is a world by itself, a prototype of the world which we see, and in this interpretation Aristotle is supported and sustained by all the later Scholastics. It is no longer seriously maintained that the Platonic Ideas exist merely in the human mind. More worthy of consideration is the view of St. Augustine, who, following the example of early Christian Platonists, identifies the world of Platonic Ideas with the mind of God. This view, supported as it is by the authority of some of the greatest of Christian philosophers as well as by that of the later Platonists and of all the Neo-Platonists, is not lightly to be set aside. On the other hand, the statements of Aristotle^[19] are explicit, and we must remember that Aristotle was an immediate disciple of Plato; we have no reason to suppose that he willfully misrepresented his master in this most important point, and we have every reason to believe that he was fully capable of understanding his master's teaching.^[20]

[17] Phaedrus, 247.

[18] Ibid., 210.

[19] Met., 1, 9, 990 b; XIII, 4, 1078; Phys., IV, 2, 209 b, et alibi.

[20] For bibliography, cf. Ritter and Preller, op. cit., p. 244, note d.

So far the Idea has been described as the objective correlative of our universal concept; but while the universality of our concepts is a product of dialectical thought, the universality of the Idea is objective, that is, independent of the human mind. This objective universality is explained in the Sophist,^[21] in which Plato attacks the Eleatic doctrine of the oneness of Being, maintaining that the Idea is at the same time one and many. But how are the unity and multiplicity of the Idea to be reconciled? Plato answers that they are reconciled by the community (koinônia) of concepts. As a concept, for example Being, is differentiated into its determinations, such as motion and rest, so in the objective order (as Plato shows in the Parmenides^[22] by a more cogent process of direct argument) the Idea is identical with another thing (tauton) and at the same time is different from other things (thateron). In this way, we have unity in plurality and plurality in unity. A Scholastic would say that the fundamental unity of the subject is not incompatible with the formal multiplicity of its qualities, and while this is not precisely what Plato meant, it is certainly a better illustration of Plato's meaning than is the Neo-Platonic interpretation, according to which by Ideas Plato meant numbers. It is, however, very likely that Plato did not clearly understand how unity and multiplicity could belong to the Idea.

[21] Cf. especially 256.

[22] Parm., 137.

Just as Plato attacked the Eleatic doctrine of the oneness of Being so did he^[23] attack the Eleatic doctrine of immobility. The Idea is active, for, if it were inert, it would be capable neither of being known by us nor of constituting reality; and to cause things to be known and to constitute their reality are, so to speak, the two functions of the Idea. Not only is the Idea described as active,^[24] but even as the only true cause. In a remarkable passage,^[25] Socrates is represented as saying that he was dissatisfied with the speculations of the Physicists, that he was disappointed in his hope that Anaxagoras would explain the origin of things, and that he finally discovered that Ideas are the only adequate causes of phenomena. Aristotle, therefore, is right in saying^[26] that he knew of no efficient causes in the doctrine of Plato except Ideas, and thus we are forced to accept without attempting to explain the Platonic doctrine that Ideas, without being caused, are causes; that although they are not subject to Becoming, they are the power by whose agency all phenomena become. Still, in justice to Plato, it should be remembered that while he maintains the dynamic function of the Ideas, holding them to be living powers, he is primarily concerned with their static, or plastic, function, inasmuch as they are the forms, or types, of existing things.

[23] Sophis., 248.

[24] Phaedo, 96 ff.

[25] Phaedo, loc. cit.

[26] Met., I, 9, 991, 992; De Gen. et Corr., II, 9, 335 b.

3. The world of Ideas. Plato hardly ever speaks of the Idea, but always of Ideas in the plural, for there is a world of Ideas. Indeed, we may say that for Plato there are three worlds: world of concrete phenomena, the world of our concepts, and the world of Ideas (kosmos, or topos noêtos). The relation between the first and third of these worlds will be discussed later under the head of Physics. The relation between the world of concepts and the world of Ideas lies in the fact that the former is the faint reflection of the latter. This is how Plato would describe it; in modern terminology we should say the world of Ideas is the logical and ontological prius of the world of concepts. But, however we view the relation between the two worlds, it cannot be denied that there is at least a parallelism between them. To every concept corresponds an Idea, and to the laws of thought which rule the world of concepts correspond the laws of Being which rule the world of Ideas.

In the first place, just as our concepts are many, the Ideas are many. Everything has its Idea, -- what is small and worthless as well as what is great and perfect. Products of art as well as objects of nature; substances, qualities, relations, mathematical figures, and grammatical forms, -- all these have their Ideas.^[27] That alone has no Idea which is mere Becoming. The number of Ideas, then, is indefinite.

[27] Cf. Parm., 130.

In the second place, our concepts possess a logical unity, and so in all the multiplicity of Ideas there is a unity which may be called organic. The Ideas form a series descending in well-ordered division and subdivision from the highest genera to the individual, and it is the task of science to represent this series, -- to descend in thought from the one to the multiple. Plato himself^[28] attempted to perform this task, naming, as the most universal Ideas, Being and not-Being, like and unlike, unity and number, the straight and the crooked, -- an attempt which suggests on the one hand the ten opposites of the Pythagoreans and on the other hand the ten Aristotelian categories. The classification is of course incomplete.

[28] Thaet., 184, 186.

Of greater importance than this incomplete enumeration of the highest kinds of Ideas is Plato's doctrine of the supremacy of the Idea of good. As in the material universe the sun is the source of light and life, illumining the earth and filling every part of it with life-producing warmth, so in the supersensible world of Ideas the Idea of good is the light and life of all the other Ideas causing them both to be and to be known.^[29] But what does Plato mean by this Idea of good? Is it merely the absolute good, acting as final cause, the goal of human activity, the ultimate end of all things? If this were Plato's meaning, the good might be defined as a final cause; it could not be defined as efficient cause, and it certainly is so described.^[30] Moreover, in the Philebus ^[31] the good is identified with divine reason. The only rational interpretation, therefore, of Plato's doctrine of the good is that by the Idea of good Plato meant God Himself. It is true that for us who are accustomed to represent the Deity as a person, it is not easy to realize how Plato could hypostatize a universal concept and call it God, or how he could conceive the source of life and energy to be intelligent, and yet describe it in terms inconsistent with self-consciousness. The correct explanation seems to be that the relation between personality and intelligence did not suggest itself to Plato. (Not only he, but the ancient philosophers in general, lacked a definite notion of what personality is. Plato, it must be understood, did not deny the personality of God. Indeed, he often speaks of God as a person. He was simply unconscious of the problem which suggests itself so naturally to us, How to reconcile the notion of personality with the Idea of good which he identified with God?

[29] Cf. Rep., VI, 508.

[30] Cf. Rep., loc. cit.

[31] Phileb., 22 C.

From the consideration of the Idea of good we are led to the next division of Plato's philosophy, namely, physics; it was because of his goodness that God created phenomena. We pass therefore, as it were, through the Idea of good, from the world of Ideas to the world of phenomena.

Physics. Under this head are included all the manifestations of the Idea in the world of phenomena. Now the world of phenomena is the world of sense-presentation, the region of change and multiplicity and imperfection and, therefore, of partial not-Being. It presents a striking contrast to the world of Ideas, which stands "in viewless majesty" above it, and where there is no change, no imperfection, no not-Being. Yet these two worlds have something in common: there is a contact (koinônia) of the lower with the higher, for the phenomenon partakes (metechei) of the Idea.^[32] Thus the concrete good (good men, good actions) partakes of the absolute good: a horse or a fire in the concrete world partakes of the horse-in-itself or of the fire-in-itself which exists in the world of Ideas. In the Parmenides^[33] the participation is explained to be an imitation (mimêsis), the Ideas being prototypes (paradeigmata) of which the phenomena are ectypes, or copies (eidôla). This participation is, however, so imperfect that in beauty and luster and grandeur the world of phenomena falls far short of the world of Ideas.

[32] Cf. Arist., Met., I, 6, 987 b, 9.

[33] Parm., 132 D.

1. Whence, we are forced to ask, comes this imperfection, this partial not-Being? For answer, Plato is obliged to assume a principle directly antithetical to the Idea. He does not call this principle matter, the word hulê being first used in this sense by Aristotle; and it is a mistake to interpret Plato's thought as if by the principle of imperfection he meant a material substratum of existence. The phrase by which it is designated varies in the different dialogues; it is called, for example, space (chôra), mass (ekmageion), receptacle (pandeches), the unlimited (apeiron), and, according to some interpreters, it is not-Being (mê on), and the great and small. It is described in the Timeaus^[34] as that in which all things appear, grow up, and decay. Consequently, it is a negative principle of limitation, more akin to space than to matter, and Aristotle is right in contrasting^[35] his own idea of the limiting principle with that of Plato. The so-called Platonic matter is essentially a negation, whereas in Aristotle's philosophy negation (steresis) is but a quality of matter.

[34] Tim., 48ff.

[35] Phys., IV, 2, 209b; ibid., 210 a.

The concept of Platonic matter is not easy to grasp. It is a mere form, yet it is not a form of the mind in any Kantian sense. It is a form objectively existing, and yet it is not a reality. Plato himself recognized the difficulty which the concept of the principle of limitation involved. In the Timaeus^[36] he tells us that it is known by a kind of spurious reason (logismô nothô) and is hardly a matter of belief. The confession does not surprise us, for in this attempt to designate a limiting principle lies the fatal flaw of the whole Platonic theory. To derive the limited from the unlimited, the partial not-Being from Being, is a task which neither Plato nor Spinoza could fulfill consistently with his first assumptions. Aristotle detected this weakness in the idealistic monism of Plato, as well as in the materialistic monism of the early Physicists, and it was in order to supply the defects of both that he introduced the dualistic concept of a world which is the outcome of the potential and the actual.

[36] Tim., 52.

Plato, therefore, failed to account satisfactorily for the derivation of the sensuous from the supersensuous world. He had recourse, as Aristotle remarks,^[37] to such widely different expressions as participation, community (koinônia), imitation ; but he must have been aware that by these phrases he evaded rather than solved the real problem. One point, however, is beyond dispute: Plato assumed that a limiting principle, the source of all evil, and imperfection, exists. He assumed it, illogically, in defiance of his doctrine that the Idea is the only reality. He is, therefore, as one who would be a dualist did his premises allow him to depart from the monism which is the starting point of all his speculation.

[37] Met., I, 6, 987 b.

2. In order to explain the world of phenomena, Plato was obliged to postulate, besides the Idea and the principle of limitation, the existence of a world-soul (Nous), which mediates between the Idea and matter and is the proximate cause of all life and order and motion and knowledge in the universe. The universe, he taught, is a living animal (zôon ennoun), endowed with the most perfect and most intelligent of souls, because, as he argues in the Timaeus,^[38] if God made the world as perfect as the nature of matter (the principle of limitation) would allow, He must have endowed it with a soul that is perfect. This soul is a perfect harmony: it contains all mathematical proportions. Diffused throughout the universe, ceaselessly self-moving according to regular law, it is the cause of all change and all Becoming. It is not an Idea, for the Idea is uncaused, universal, all-Being, while the world-soul is derived and particular and is partly made up of not-Being. Although it is conceived by a kind of analogy with the human soul, the question whether it is personal or impersonal never suggested itself to Plato.^[39]

[38] Tim., 30, 35.

[39] Cf. Zeller, Plato, p. 358.

After the general problem of the derivation of the sensuous from the supersensuous world come the particular questions which belong to what we call cosmology. Plato himself informs us^[40] that since nature is Becoming rather than Being, the study of nature leads not to true scientific knowledge (epistême), but to belief only (pistis). Cosmology, therefore, and physical science in general have a value far inferior to dialectic, which is the science of the pure Idea.

[40] Tim., 59 C.

3. As to the origin of the universe: The so-called Platonic matter is eternal. The universe, however, as it exists had its origin in time. This seems to be the natural and obvious sense of Timeus, 28, although Xenocrates, an immediate disciple of Plato, was of opinion that Plato taught the temporal origin of the world merely for the sake of clearness -- to emphasize the fact that it had an origin. Now, since matter existed from eternity, the universe was not created. From out the chaos which was ruled by necessity (anagke), God, the Demiurgos, or Creator, brought order, fashioning the phenomena in matter according to the eternal prototypes, the Ideas, and making the phenomena -- for He was free from jealousy -- as perfect as the imperfection of matter would allow. First, He produced the world-soul; then, as the sphere is the most perfect figure, He formed for this soul a spherical body composed of fire, air, earth, and water -- substances which Empedocles had designated as the root principles of the world, and which are now, for the first time in the history of philosophy, called elements. The question, Why are the elements four in number? Plato answers by assigning a teleological as well as a physical reason,^[41] thus exhibiting the two influences, Socratic and Pythagorean, which more than any other causes contributed to determine his physical theories. The four elements differ from one another by the possession of definite qualities; all differences of things are accounted for by different combinations of the elements themselves -- bodies are light or heavy according as the element of fire, which is light, or the element of earth, which is heavy, prevails.

[41] Cf. Tim., 31 B.

4. In his explanation of the world-system as it now is, Plato shows still more evidently the influence of the Pythagoreans, and especially of Philolaus.^[42] Add to this influence the natural tendency of Plato's mind towards the idealistic and artistic concept of everything, and the doctrine that the heavenly bodies are created gods -- the most perfect of God's creatures, from whose fidelity to their paths in the firmament man may learn to rule the lawless movements of his own soul^[43] -- will cease to appear out of keeping with the seriousness of Plato's attempt to solve the problems of human knowledge and human destiny.

[42] Cf. ibid., 33 B.

[43] Cf. ibid.,38 E.

5. In Plato's anthropological doctrines the mixture of myth and science is more frequent and more misleading than in any other portion of his philosophy. As to the origin of the soul, he teaches^[44] that when the Creator had formed the universe and the stars He commanded the created gods to fashion the human body, while He Himself proceeded to form the human soul (or at least the rational part of it), taking for this purpose the same materials which He had used to form the world-soul, mixing them in the same cup, though the mixture was of inferior purity.

[44] Ibid., 41 A

Plato rejects^[45] the doctrine that the soul is a harmony of the body, on the ground that the soul has strivings which are contrary to the inclinations of sense, and which prove it to be of a nature different from that of the body. The soul is expressly defined^[46] as a self-moving principle. It is related to the body merely as a causa movens. How, then, did it come to be united to the body? Plato^[47] answers by the "figure," or allegory, in which is conveyed the doctrine of preëxistence. In the Timaeus, however, the mythical form of expression is laid aside, as when, for example,^[48] the soul is said to have been united to the body by virtue of a cosmic law.

[45] Phaedo, 93, 95.

[46] Phaedrus, 245 C.

[47] Ibid., 246 ff.

[48] Timaeus, 41 D.

The doctrine of preëxistence gave rise to the doctrine of recollection, although sometimes, as in the Meno,^[49] the previous existence of the soul is proved from the possibility of learning. The doctrine of recollection implies that in our supercelestial home the soul enjoyed a clear and unclouded vision of the Ideas, and that, although it fell from that happy state and was steeped in the river of forgetfulness, it still retains an indistinct memory of those heavenly intuitions of the truth; so that the sight of the phenomena -- mere shadows of the Ideas -- arouses in the soul a clearer and fuller recollection of what it contemplated in its previous existence. The process of learning consists, therefore, in recalling what we have forgotten: to learn is to remember.

[49] Meno, 81.

If preëxistence is one pole in the ideal circle of the soul's existence, immortality is the other. The sojourn of the soul in the world of ever-changing phenomena is but a period of punishment which ends with the death of the body. Underlying the mythical language in which Plato conveyed his psychological doctrines, there is a deep-seated conviction of the reality of the future life, a genuine belief in the immortality of the soul. Indeed, Plato is the first Greek philosopher to formulate in scientific language and to establish with scientific proof an answer to the question, Does death end all things? Hitherto, the immortality of the soul had been part of the religious systems of Asia and of Greece; now it appears for the first time as a scientific thesis, as part of a purely rational system of philosophy.

The dialogue which deals expressly with the problem of immortality is the Phaedo; there Socrates is represented by the narrator as discoursing on the future existence, while the jailer stands at the door of the prison with the fatal draught in his hand. The arguments which Socrates uses may be summed up as follows:

1. Opposites generate opposites. Out of life comes death: therefore, out of death comes life.^[50]

[50] Phaedo, 70 E.

2. The soul, being without composition, is akin to the absolutely immutable Idea. The body, on the contrary, is, by its composition, akin to things which change. When the body is destroyed, the soul, by virtue of its affinity to the indestructible, is enabled to resist all decay and destruction.^[51]

[51] Op. cit., 78-81.

3. If the soul existed before the body, it is natural to expect that it will exist after the body. That it existed before the body is proved by the doctrine of recollection.^[52]

[52] Op. cit., 72-79.

4. Besides these arguments, the following proof is used by Plato.^[53] The dissolution of anything is accomplished by the evil which is opposed to it. Now, moral evil is the only evil which is opposed to the nature of the soul; if, then, sin does not destroy the soul, -- as it certainly does not, -- the reason must be that the soul is indestructible.

[53] Rep., X, 609.

Underlying all the foregoing arguments is the one pivotal thought of Plato's psychology, that life necessarily belongs to the Idea of the soul. This thought is brought out in the last of the Socratic arguments.

5. An Idea cannot pass into its opposite, -- a Scholastic would say essences are immutable. An Idea, therefore, which has a definite concept attached to it excludes the opposite of that concept. Now, life belongs to the Idea of the soul. Consequently, the soul excludes death, which is the opposite of life. A dead soul is a contradiction in terms.^[54]

[54] Phaedo, 103 ff.

The same ontological argument occurs in Phaedrus, 245, and it is evidently the chief argument on which Plato bases his conviction that the soul is immortal. Yet in the Phaedo, after each of Socrates' listeners has signified his acceptance of the proof, Socrates is made to agree with Simmias that there is no longer room for any uncertainty except that which arises from the greatness of the subject and the feebleness of the human mind.^[55]

[55] Op. cit., 107.

Closely allied with the doctrine of immortality is the doctrine of transmigration of souls and of future retribution. Plato recognized that immortality involves the idea of future retribution of some sort, just as the necessity of a future retribution involves immortality. He did not determine scientifically the precise nature of retribution in the next life. He was content with adopting the transmigration myths which he derived from the mysteries. Yet, for Plato, these myths contained a germ of truth, although the most that can be safely said is that he seriously maintained the doctrine of transmigration in a generic sense: the details so carefully set forth in the Timaeus and in the Phaedo are not to be taken as part of Plato's scientific thought.

When we speak of immortality we must not imagine that Plato held every part of the soul to be immortal. He enumerates three parts of the soul, -- the rational (logos), the irascible (thumos), and the appetitive (epithumia) parts. These are not faculties or powers of one substance, but parts (merê) the distinction of which is proved by the fact that appetite strives against reason, and anger against reason and appetite.^[56] Reason resides in the head; the irascible soul, the seat of courage, is in the heart; and appetite, the seat of desire, is in the abdomen.^[57]

[56] Rep., IV, 436 A.

[57] Cf. Cicero, Tusculanae Disputationes, I, 20.

Of these three, the rational part alone is immortal. It alone is produced by God. By maintaining that the soul has parts Plato weakens his doctrine of immortality and exposes it to many objections.

Plato in his theory of knowledge bases his distinction of kinds of knowledge on the distinction of objects. Objects of knowledge^[58] are divided as follows:

Supersensible objects (Noêton genos)
- Ideas (Ideai)
- Mathematical entities (Mathêmatika)
Sensible objects (Horaton genos)
- Real bodies (Sômata)
- Semblances of bodies (Eikones)

[58] Cf. Rep., VI, 509; Ueberweg, op. cit., p. 122

To this corresponds the division of knowledge:

Supersensible knowledge (Noêsis)
- Intellect (Nous)
- Reason (Dianoia)
Opinion: sense-knowledge (Doxa)
- Sense-perception (Pistis)
- Imagination (Eikasia)