Chapter XII: Plato (1)

None of the predecessors of Plato had constructed a system of philosophy. What they had produced, and in great abundance, were isolated philosophical ideas, theories, hints, and suggestions. Plato was the first person in the history of the world to produce a great all-embracing system of philosophy, which has its ramifications in all departments of thought and reality. In doing this, Plato laid all previous thought under contribution. He gathered the entire harvest of Greek philosophy. All that was best in the Pythagoreans, the Eleatics, Heracleitus, and Socrates, reappears, transfigured in the system of Plato. But it is not to be imagined, on this account, that Plato was a mere eclectic, or a plagiarist, who took the best thoughts of others, and worked them into some sort of a patch-work philosophy of his own. He was, on the contrary, in the highest degree an original thinker. But like all great systems of thought, that of Plato grows out of the thought of previous thinkers. He does indeed appropriate the ideas of Heracleitus, Parmenides, and Socrates. But he does not leave them as he finds them. He takes them as the germs of a new development. They are the foundations, below ground, upon which he builds the palace of philosophy. In his hands, all previous thought becomes {165} transfigured under the light of a new and original principle.

1. Life and Writings.

The exact date of the birth of Plato is a matter of doubt. But the date usually given, 429-7 B.C. cannot be far wrong. He came of an aristocratic Athenian family, and was possessed of sufficient wealth to enable him to command that leisure which was essential for a life devoted to philosophy. His youth coincided with the most disastrous period of Athenian history. After a bitter struggle, which lasted over a quarter of a century, the Peloponnesian war ended in the complete downfall of Athens as a political power. And the internal affairs of the State were in no less confusion than the external. Here, as elsewhere, a triumphant democracy had developed into mob-rule. Then at the close of the Peloponnesian war, the aristocratic party again came into power with the Thirty Tyrants, among whom were some of Plato's own relatives. But the aristocratic party, so far from improving affairs, plunged at once into a reign of bloodshed, terror, and oppression. These facts have an important bearing upon the history of Plato's life. If he ever possessed any desire to adopt a political career, the actual condition of Athenian affairs must have quenched it. An aristocrat, both in thought and by birth, he could not accommodate himself to the rule of the mob. And if he ever imagined that the return of the aristocracy to power would improve matters, he must have been bitterly disillusioned by the proceedings of the Thirty Tyrants. Disgusted alike with the democracy and the aristocracy he seems to have retired into seclusion. He never once, throughout his long life, appeared as a {166} speaker in the popular assembly. He regarded the Athenian constitution as past help.

Not much is known of the philosopher's youth. He composed poems. He was given the best education that an Athenian citizen of those days could obtain. His teacher, Cratylus, was a follower of Heracleitus, and Plato no doubt learned from him the doctrines of that philosopher. It is improbable that he allowed himself to remain unacquainted with the disputations of the Sophists, many of whom were his own contemporaries. He probably read the book of Anaxagoras, which was easily obtainable in Athens at the time. But on all these points we have no certain information. What we do know is that the decisive event in his youth, and indeed in his life, was his association with Socrates.

For the last eight years of the life of Socrates, Plato was his friend and his faithful disciple. The teaching and personality of the master constituted the supreme intellectual impulse of his life, and the inspiration of his entire thought. And the devotion and esteem which he felt for Socrates, so far from waning as the years went by, seem, on the contrary, to have grown continually stronger. For it is precisely in the latest dialogues of his long life that some of the most charming and admiring portraits of Socrates are to be found. Socrates became for him the pattern and exemplar of the true philosopher.

After the death of Socrates a second period opens in the life of Plato, the period of his travels. He migrated first to Megara, where his friend and fellow-disciple Euclid was then founding the Megaric school. The Megaric philosophy was a combination of the thought of Socrates with that of the Eleatics. And it was no doubt here, at {167} Megara, under the influence of Euclid, that Plato formed his deeper acquaintance with the teaching of Parmenides, which exercised an all-important influence upon his own philosophy. From Megara he travelled to Cyrene, Egypt, Italy, and Sicily. In Italy he came in contact with the Pythagoreans. And to the effects of this journey may be attributed the strong Pythagorean elements which permeate his thought.

In Sicily he attended the court of Dionysius the Elder, tyrant of Syracuse. But here his conduct seems to have given grave offence. Dionysius was so angered by his moralizings and philosophical diatribes that he put Plato up to auction in the slave market. Plato narrowly escaped the fate of slavery, but was ransomed by Anniceris, the Cyrenaic. He then returned to Athens, his travels having occupied a period of about ten years.

With the return of Plato to Athens we enter upon the third and last period of his life. With the exception of two journeys to be mentioned shortly, he never again left Athens. He now appeared for the first time as a professional teacher and philosopher. He chose for the scene of his activities a gymnasium, called the Academy. Here he gradually collected round him a circle of pupils and disciples. For the rest of his life, a period of about forty years, he occupied himself in literary activity, and in the management of the school which he had founded. His manner of life was in strong contrast to that of Socrates. Only in one respect did he resemble his master. He took no fees for his teaching. Otherwise the lives of the two great men bear no resemblance to each other. Socrates had gone out into the highways and byways in search of wisdom. He had wrangled in {168} the market-place with all comers. Plato withdrew himself into the seclusion of a school, protected from the hubbub of the world by a ring of faithful disciples. It was not to be expected that a man of Plato's refinement, culture, and aristocratic feelings, should appreciate, as Socrates, the man of the people, had done, the rough-and-tumble life of the Athenian market-place. Nor was it desirable for the advancement of philosophy that it should be so. The Socratic philosophy had suffered from the Socratic manner of life. It was unmethodical and inchoate. Systematic thought is not born of disputes at the street corner. For the development of a great world-system, such as that of Plato, laborious study and quiet seclusion were essential.

This period of Plato's mastership was broken only by two journeys to Sicily, both undertaken with political objects. Plato knew well that the perfect State, as depicted in his "Republic," was not capable of realization in the Greece of his own time. Nevertheless, he took his political philosophy very seriously. Though the perfect republic was an unattainable ideal, yet, he thought, any real reform of the State must at least proceed in the direction of that ideal. One of the essential principles of the "Republic" was that the rulers must also be philosophers. Not till philosopher and ruler were combined in one and the same person could the State be governed upon true principles. Now, in the year 368 B.C., Dionysius the Elder died, and Dionysius the younger became tyrant of Syracuse. Dionysius despatched an invitation to Plato to attend his court and give him the benefit of his advice. Here was an opportunity to experiment. Plato could train and educate a {169} philosopher-king. He accepted the invitation. But the expedition ended disastrously. Dionysius received him with enthusiasm, and interested himself in the philosophical discourses of his teacher. But he was young, impetuous, hot-headed, and without genuine philosophic bent. His first interest gave place to weariness and irritation. Plato left Syracuse a disappointed man; and returned to Athens. Nevertheless, after the lapse of a few years, Dionysius again invited him to Syracuse, and again he accepted the invitation. But the second journey ended in disaster like the first, and Plato was even in danger of his life, but was rescued by the intervention of the Pythagoreans. He returned to Athens in his seventieth year, and lived till his death in the seclusion of his school, never again attempting to intervene in practical politics.

For more than another decade he dwelt and taught in Athens. His life was serene, quiet, and happy. He died peacefully at the age of eighty-two.

Plato's writings take the form of dialogues. In the majority of these, the chief part is taken by Socrates, into whose mouth Plato puts the exposition of his own philosophy. In a few, as for example the "Parmenides," other speakers enunciate the Platonic teaching, but even in these Socrates always plays an important _role_. Plato was not only a philosopher, but a consummate literary artist. The dialogues are genuinely dramatic, enlivened by incident, humour, and life-like characterization. Not only is the portrait of Socrates drawn with loving affection, but even the minor characters are flesh and blood.

A most important element of Plato's style is his use of myths. He does not always explain his meaning in {170} the form of direct scientific exposition. He frequently teaches by allegories, fables, and stories, all of which may be included under the one general appellation of Platonic myths. These are often of great literary beauty, but in spite of this they involve grave disadvantages. Plato slips so easily from scientific exposition into myth, that it is often no easy matter to decide whether his statements are meant literally or allegorically. Moreover, the myths usually signify a defect in his thought itself. The fact is that the combination of poet and philosopher in one man is an exceedingly dangerous combination. I have explained before that the object of philosophy is, not merely to feel the truth, as the poet and mystic feel it, but intellectually to comprehend it, not merely to give us a series of pictures and metaphors, but a reasoned explanation of things upon scientific principles. When a man, who is at once a poet and a philosopher, cannot rationally explain a thing, it is a terrible temptation to him to substitute poetic metaphors for the explanation which is lacking. We saw, for example, that the writers of the Upanishads, who believed that the whole world issues forth from the one, absolute, imperishable, being, which they called Brahman, being unable to explain why the One thus differentiates itself into the many, took refuge in metaphors. As the sparks from the substantial fire, so, they say, do all finite beings issue forth from the One. But this explains nothing, and the aim of the philosopher is not thus vaguely to feel, but rationally to understand. Now this is not merely my view of the functions of philosophy. It is emphatically Plato's own view. In fact Plato was the originator of it. He is perpetually insisting that {171} nothing save full rational comprehension deserves the names of knowledge and philosophy. No writer has ever used such contemptuous language as Plato used of the mere mystic and poet, who says wise and beautiful things, without in the least understanding why they are wise and beautiful. No man has formed such a low estimate of the functions of the poet and mystic. Plato is, in theory at least, the prince of rationalists and intellectualists. In practice, however, he must be convicted of the very fault he so severely censured in others. This, in fact, is the explanation of most of the Platonic myths. Wherever Plato is unable to explain anything, he covers up the gap in his system with a myth. This is particularly noticeable, for example, in the "Timaeus." Plato having, in other dialogues, developed his theory of the nature of the ultimate reality, arrives, in the "Timaeus," at the problem how the actual world is to be explained from that ultimate reality. At this point, as we shall see, Plato's system breaks down. His account of the absolute reality is defective, and in consequence, it affords no principle whereby the actual universe can be explained. In the "Timaeus," therefore, instead of a reasoned explanation, he gives us a series of wholly fanciful myths about the origin of the world. Wherever we find myths in Plato's dialogues, we may suspect that we have arrived at one of the weak points of the system.

If we are to study Plato intelligently, it is essential that we should cease to regard the dialogues as if they were all produced _en bloc_ from a single phase of their author's mind. His literary activity extended over a period of not less than fifty years. During that time, he did not stand still. His thought, and his mode of {172} expression, were constantly developing. If we are to understand Plato, we must obtain some clue to enable us to trace this development. And this means that we must know something of the order in which the dialogues were written. Unfortunately, however, they have not come down to us dated and numbered. It is a matter of scholarship and criticism to deduce the period at which any dialogue was written from internal evidences. Many minor points are still undecided, as well as a few questions of importance, such as the date of the "Phaedrus," [Footnote 11] which some critics place quite early and some very late in Plato's life. Neglecting these points, however, we may say in general that unanimity has been reached, and that we now know enough to be able to trace the main lines of development.

[Footnote 11: The same remark applies to the "Symposium," the "Republic," and the "Theaetetus."]

The dialogues fall into three main groups, which correspond roughly to the three periods of Plato's life. Those of the earliest group were written about the time of the death of Socrates, and before the author's journey to Megara. Some of them may have been written before the death of Socrates. This group includes the "Hippias Minor," the "Lysis," the "Charmides," the "Laches," the "Euthyphro," the "Apology," the "Crito," and the "Protagoras." The "Protagoras" is the longest, the most complex in thought, and the most developed. It is probably the latest, and forms the bridge to the second group.

All these early dialogues are short and simple, and are still, as regards their thought, entirely under the influence of Socrates. Plato has not as yet developed {173} any philosophy of his own. He propounds the philosophy of Socrates almost unaltered. Even so, however, he is no mere plagiarist. There are throughout these dialogues evidences of freshness and originality, but these qualities exhibit themselves rather in the literary form than in the philosophical substance. We find here all the familiar Socratic propositions, that virtue is knowledge, is one, is teachable; that all men seek the good, but that men differ as to what the good is; that a man who does wrong deliberately is better than a man who does it unintentionally; and so on. Moreover, just as Socrates had occupied himself in attempting to fix the concepts of the virtues, asking "what is prudence?", "what is temperance?", and the like, so in many of these dialogues Plato pursues similar inquiries. The "Lysis" discusses the concept of friendship, the "Charmides" of temperance, the "Laches" of bravery. On the whole, the philosophical substance of these early writings is thin and meagre. There is a preponderance of incident and much biographical detail regarding Socrates. There is more art than matter. Consequently, from a purely literary point of view, these are among the most charming of Plato's dialogues, and many of them, such as the "Apology" and the "Crito," are especially popular with those who care for Plato rather as an artist than as a philosopher.

The second group of dialogues is generally connected with the period of Plato's travels. In addition to the influence of Socrates, we have now the influence of the Eleatics, which naturally connects these dialogues with the period of the philosopher's sojourn at Megara. But it is in these dialogues, too, that Plato for the first time {174} develops his own special philosophical thesis. This is in fact his great constructive period. The central and governing principle of his philosophy is the theory of Ideas. All else hinges on this, and is dominated by this. In a sense, his whole philosophy is nothing but the theory of Ideas and what depends upon it. It is in this second period that the theory of Ideas is founded and developed, and its relationship to the Eleatic philosophy of Being discussed. We have here the spectacle of Plato's most original thoughts in the pangs of childbirth. He is now at grips with the central problems of philosophy. He is intent upon the thought itself, and cares little for the ornaments of style. He is struggling to find expression for ideas newly-formed in his mind, of which he is not yet completely master, and which he cannot manipulate with ease. Consequently, the literary graces of the first period recede into the background. There is little incident, and no humour. There is nothing but close reasoning, hard and laborious discussion.

The twin dialogues, "Gorgias" and "Theaetetus" are probably the earliest of this group. They result in nothing very definite, and are chiefly negative in character. Plato is here engaged merely in a preparatory clearing of the ground. The "Gorgias" discusses and refutes the Sophistic identification of virtue and pleasure, and attempts to show, as against it, that the good must be something objectively existent, and independent of the pleasure of the individual. The "Theaetetus," similarly, shows that truth is not, as the Sophists thought, merely the subjective impression of the individual, but is something objectively true in itself. The other {175} dialogues of the group are the "Sophist," the "Statesman," and the "Parmenides." The "Sophist" discusses Being and not-being, and their relationship to the theory of Ideas. The "Parmenides" inquires whether the absolute reality is to be regarded, in the manner of the Eleatics, as an abstract One. It gives us, therefore, Plato's conception of the relation of his own philosophy to Eleaticism.

The dialogues of the third group are the work of Plato's maturity. He has now completely mastered his thought, and turns it with ease in all directions. Hence the style returns to the lucidity and purity of the first period. If the first period was marked chiefly by literary grace, the second by depth of thought, the third period combines both. The perfect substance is now moulded in the perfect form. But a peculiarity of all the dialogues of this period is that they take it for granted that the theory of Ideas is already established and familiar to the reader. They proceed to apply it to all departments of thought. The second period was concerned with the formulation and proof of the theory of Ideas, the third period undertakes its systematic application. Thus the "Symposium," which has for its subject the metaphysic of love, attempts to connect man's feeling for beauty with the intellectual knowledge of the Ideas. The "Philebus" applies the theory of Ideas to the sphere of ethics, the "Timaeus" to the sphere of physics, and the "Republic" to the sphere of politics. The "Phaedo" founds the doctrine of the immortality of the soul upon the theory of Ideas. The "Phaedrus" is probably to be grouped with the "Symposium." The beauty, grace, and lucidity of the style, and the fact that it assumes throughout that {176} the theory of Ideas is a thing established, lead us to the belief that it belongs to the period of Plato's maturity. Zeller's theory that it was written at the beginning of the second period, and is then offered to the reader as a sort of sweetmeat to induce him to enter upon the laborious task of reading the "Sophist," the "Statesman," and the "Parmenides," seems to be far-fetched and unnecessary. [Footnote 12]

[Footnote 12: Zeller's _Plato and the Older Academy_, chap. iii.]

If the second is the great constructive period of Plato's life, the third may be described as his systematic and synthetic period. Every part of his philosophy is here linked up with every other part. All the details of the system are seen to flow from the one central principle of his thought, the theory of Ideas. Every sphere of knowledge and being is in turn exhibited in the light of that principle, is permeated and penetrated by it.

The plan for expounding Plato which first suggests itself is to go through the dialogues, one by one, and extract the doctrine of each successively. But this suggestion has to be given up as soon as it is mentioned. For although the philosophy of Plato is in itself a systematic and coherent body of thought, he did not express it in a systematic way. On the contrary, he scatters his ideas in all directions. He throws them out at random in any order. What logically comes first often appears last. It may be found at the end of a dialogue, and the next step in reasoning may make its appearance at the beginning, or even in a totally different dialogue. If, therefore, we are to get any connected view of the system, we must abandon Plato's own order of exposition, and piece the thought together for ourselves. We must begin {177} with what logically comes first, wherever we may find it, and proceed with the exposition in the same manner.

A similar difficulty attends the question of the division of Plato's philosophy. He himself has given us no single and certain principle of division. But the principle usually adopted divides his philosophy into Dialectic, Physics, and Ethics. Dialectic, or the theory of Ideas, is Plato's doctrine of the nature of the absolute reality. Physics is the theory of phenomenal existence in space and time, and includes therefore the doctrine of the soul and its migrations, since these are happenings in time. Ethics includes politics, the theory of the duty of man as a citizen, as well as the ethics of the individual. Certain portions of the system, the doctrine of Eros, for example, do not fall very naturally into any of these divisions. But, on the other hand, though some dialogues are mixed as to their subject matter, others, and those the most important, fall almost exclusively into one or other division. For example, the "Timaeus," the "Phaedo," and the "Phaedrus," are physical. The "Philebus," the "Gorgias," and the "Republic," are ethical. The "Theaetetus," the "Sophist," and the "Parmenides," are dialectical.

2. The Theory of Knowledge.

The theory of Ideas is itself based upon the theory of knowledge. What is knowledge? What is truth? Plato opens the discussion by telling us first what knowledge and truth are not. His object here is the refutation of false theories. These must be disposed of to clear the ground preparatory to positive exposition. The first such false theory which he attacks is that knowledge {178} is perception. To refute this is the main object of the "Theaetetus." His arguments may be summarized as follows:--

(1) That knowledge is perception is the theory of Protagoras and the Sophists, and we have seen to what results it leads. What it amounts to is that what appears to each individual true is true for that individual. But this is at any rate false in its application to our judgment of future events. The frequent mistakes which men make about the future show this. It may appear to me that I shall be Chief Justice next year. But instead of that, I find myself, perhaps, in prison. In general, what appears to each individual to be the truth about the future frequently does not turn out so in the event.

(2) Perception yields contradictory impressions. The same object appears large when near, small when removed to a distance. Compared with some things it is light, with others heavy. In one light it is white, in another green, and in the dark it has no colour at all. Looked at from one angle this piece of paper seems square, from another it appears to be a rhombus. Which of all these impressions is true? To know which is true, we must be able to exercise a choice among these varying impressions, to prefer one to another, to discriminate, to accept this and reject that. But if knowledge is perception, then we have no right to give one perception preference over another. For all perceptions are knowledge. All are true.

(3) This doctrine renders all teaching, all discussion, proof, or disproof, impossible. Since all perceptions are equally true, the child's perceptions must be just as much the truth as those of his teachers. His teachers, {179} therefore, can teach him nothing. As to discussion and proof, the very fact that two people dispute about anything implies that they believe in the existence of an objective truth. Their impressions, if they contradict each other, cannot both be true. For if so, there is nothing to dispute about. Thus all proof and refutation are rendered futile by the theory of Protagoras.

(4) If perception is truth, man is the measure of all things, in his character as a percipient being. But since animals are also percipient beings, the lowest brute must be, equally with man, the measure of all things.

(5) The theory of Protagoras contradicts itself. For Protagoras admits that what appears to me true is true. If, therefore, it appears to me true that the doctrine of Protagoras is false, Protagoras himself must admit that it is false.

(6) It destroys the objectivity of truth, and renders the distinction between truth and falsehood wholly meaningless. The same thing is true and false at the same time, true for you and false for me. Hence it makes no difference at all whether we say that a proposition is true, or whether we say that it is false. Both statements mean the same thing, that is to say, neither of them means anything. To say that whatever I perceive is true for me merely gives a new name to my perception, but does not add any value to it.

(7) In all perception there are elements which are not contributed by the senses. Suppose I say, "This piece of paper is white." This, we might think, is a pure judgment of perception. Nothing is stated except what I perceive by means of my senses. But on consideration it turns out that this is not correct. First of all I must {180} think "this piece of paper." Why do I call it paper? My doing so means that I have classified it. I have mentally compared it with other pieces of paper, and decided that it is of a class with them. My thought, then, involves comparison and classification. The object is a compound sensation of whiteness, squareness, etc. I can only recognise it as a piece of paper by identifying these sensations, which I have now, with sensations received from other similar objects in the past. And not only must I recognize the sameness of the sensations, but I must recognize their difference from other sensations. I must not confound the sensations I receive from paper with those which I receive from a piece of wood. Both identities and differences of sensations must be known before I can say "this piece of paper." The same is true when I go on to say that it "is white." This is only possible by classifying it with other white objects, and differentiating it from objects of other colours. But the senses themselves cannot perform these acts of comparison and contrast. Each sensation is, so to speak, an isolated dot. It cannot go beyond itself to compare itself with others. This operation must be performed by my mind, which acts as a co-ordinating central authority, receiving the isolated sensations, combining, comparing, and contrasting them. This is particularly noticeable in cases where we compare sensations of one sense with those of another. Feeling a ball with my fingers, I say it feels round. Looking at it with my eyes, I say it looks round. But the feel is quite a different sensation from the look. Yet I use the same word, "round," to describe both. And this shows that I have identified the two sensations. This {181} cannot be done by the senses themselves. For my eyes cannot feel, and my fingers cannot see. It must be the mind itself, standing above the senses, which performs the identification. Thus the ideas of identity and difference are not yielded to me by my senses. The intellect itself introduces them into things. Yet they are involved in all knowledge, for they are involved even in the simplest acts of knowledge, such as the proposition, "This is white." Knowledge, therefore, cannot consist simply of sense-impressions, as Protagoras thought, for even the simplest propositions contain more than sensation.

If knowledge is not the same as perception, neither is it, on the other hand, the same as opinion. That knowledge is opinion is the second false theory that Plato seeks to refute. Wrong opinion is clearly not knowledge. But even right opinion cannot be called knowledge. If I say, without any grounds for the statement, that there will be a thunderstorm next Easter Sunday, it may chance that my statement turns out to be correct. But it cannot be said that, in making this blind guess, I had any knowledge, although, as it turned out, I had right opinion. Right opinion may also be grounded, not on mere guess-work, but on something which, though better, is still not true understanding. We often feel intuitively, or instinctively, that something is true, though we cannot give any definite grounds for our belief. The belief may be quite correct, but it is not, according to Plato, knowledge. It is only right opinion. To possess knowledge, one must not only know that a thing is so, but why it is so. One must know the reasons. Knowledge must be full and complete understanding, rational comprehension, and not mere instinctive belief. {182} It must be grounded on reason, and not on faith. Right opinion may be produced by persuasion and sophistry, by the arts of the orator and rhetorician. Knowledge can only be produced by reason. Right opinion may equally be removed by the false arts of rhetoric, and is therefore unstable and uncertain. But true knowledge cannot be thus shaken. He who truly knows and understands cannot be robbed of his knowledge by the glamour of words. Opinion, lastly, may be true or false. Knowledge can only be true.

These false theories being refuted, we can now pass to the positive side of the theory of knowledge. If knowledge is neither perception nor opinion, what is it? Plato adopts, without alteration, the Socratic doctrine that all knowledge is knowledge through concepts. This, as I explained in the lecture on Socrates, gets rid of the objectionable results of the Sophistic identification of knowledge with perception. A concept, being the same thing as a definition, is something fixed and permanent, not liable to mutation according to the subjective impressions of the individual. It gives us objective truth. This also agrees with Plato's view of opinion. Knowledge is not opinion, founded on instinct or intuition. Knowledge is founded on reason. This is the same as saying that it is founded upon concepts, since reason is the faculty of concepts.

But if Plato, in answering the question, "What is knowledge?" follows implicitly the teaching of Socrates, he yet builds upon this teaching a new and wholly un-Socratic metaphysic of his own. The Socratic theory of knowledge he now converts into a theory of the nature of reality. This is the subject-matter of Dialectic.

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3. Dialectic, or the Theory of Ideas.

The concept had been for Socrates merely a rule of thought. Definitions, like guide-rails, keep thought upon the straight path; we compare any act with the definition of virtue in order to ascertain whether it is virtuous. But what was for Socrates merely regulative of thought, Plato now transforms into a metaphysical substance. His theory of Ideas is the theory of the objectivity of concepts. That the concept is not merely an idea in the mind, but something which has a reality of its own, outside and independent of the mind--this is the essence of the philosophy of Plato.

How did Plato arrive at this doctrine? It is founded upon the view that truth means the correspondence of one's ideas with the facts of existence. If I see a lake of water, and if there really is such a lake, then my idea is true. But if there is no lake, then my idea is false. It is an hallucination. Truth, according to this view, means that the thought in my mind is a copy of something outside my mind. Falsehood consists in having an idea which is not a copy of anything which really exists. Knowledge, of course, means knowledge of the truth. And when I say that a thought in my mind is knowledge, I must therefore mean that this thought is a copy of something that exists. But we have already seen that knowledge is the knowledge of concepts. And if a concept is true knowledge, it can only be true in virtue of the fact that it corresponds to an objective reality. There must, therefore, be general ideas or concepts, outside my mind. It were a contradiction to suppose, on the one hand, that the concept is true knowledge, and on the other, that it corresponds to nothing external {184} to us. This would be like saying that my idea of the lake of water is a true idea, but that no such lake really exists. The concept in my mind must be a copy of the concept outside it.

Now if knowledge by concepts is true, our experiences through sensation must be false. Our senses make us aware of many individual horses. Our intellect gives us the concept of the horse in general. If the latter is the sole truth, the former must be false. And this can only mean that the objects of sensation have no true reality. What has reality is the concept; what has no reality is the individual thing which is perceived by the senses. This and that particular horse have no true being. Reality belongs only to the idea of the horse in general.

Let us approach this theory from a somewhat different direction. Suppose I ask you the question, "What is beauty?" You point to a rose, and say, "Here is beauty." And you say the same of a woman's face, a piece of woodland scenery, and a clear moonlight night. But I answer that this is not what I want to know. I did not ask what things are beautiful, but what is beauty. I did not ask for many things, but for one thing, namely, beauty. If beauty is a rose, it cannot be moonlight, because a rose and moonlight are quite different things. By beauty we mean, not many things, but one. This is proved by the fact that we use only one word for it. And what I want to know is what this one beauty is, which is distinct from all beautiful objects. Perhaps you will say that there is no such thing as beauty apart from beautiful objects, and that, though we use one word, yet this is only a manner of {185} speech, and that there are in reality many beauties, each residing in a beautiful object. In that case, I observe that, though the many beauties are all different, yet, since you use the one word to describe them all, you evidently think that they are similar to each other. How do you know that they are similar? Your eyes cannot inform you of this similarity, because it involves comparison, and we have already seen that comparison is an act of the mind, and not of the senses. You must therefore have an idea of beauty in your mind, with which you compare the various beautiful objects and so recognise them as all resembling your idea of beauty, and therefore as resembling each other. So that there is at any rate an idea of one beauty in your mind. Either this idea corresponds to something outside you, or it does not. In the latter case, your idea of beauty is a mere invention, a figment of your own brain. If so, then, in judging external objects by your subjective idea, and in making it the standard of whether they are beautiful or not, you are back again at the position of the Sophists. You are making yourself and the fancies of your individual brain the standard of external truth. Therefore, the only alternative is to believe that there is not only an idea of beauty in your mind, but that there is such a thing as the one beauty itself, of which your idea is a copy. This beauty exists outside the mind, and it is something distinct from all beautiful objects.

What has been said of beauty may equally be said of justice, or of goodness, or of whiteness, or of heaviness. There are many just acts, but only one justice, since we use one word for it. This justice must be a real thing, distinct from all particular just acts. Our ideas of justice {186} are copies of it. So also there are many white objects, but also the one whiteness.

Of the above examples, several are very exalted moral ideas, such as beauty, justice, and goodness. But the case of whiteness will serve to show that the theory attributes reality not only to exalted ideas, but to others also. In fact, we might quite well substitute evil for goodness, and all the same arguments would apply. Or we might take a corporeal object such as the horse, and ask what "horse" means. It does not mean the many individual horses, for since one word is used it must mean one thing, which is related to individual horses, just as whiteness is related to individual white things. It means the universal horse, the idea of the horse in general, and this, just as much as goodness or beauty, must be something objectively real.

Now beauty, justice, goodness, whiteness, the horse in general, are all concepts. The idea of beauty is formed by including what is common to all beautiful objects, and excluding those points in which they differ. And this, as we have seen, is just what is meant by a concept. Plato's theory, therefore, is that concepts are objective realities. And he gives to these objective concepts the technical name Ideas. This is his answer to the chief question of philosophy, namely, what, amid all the appearances and unrealities of things, is that absolute and ultimate reality, from which all else is to be explained? It consists, for Plato, in Ideas.

Let us see next what the characteristics of the Ideas are. In the first place, they are substances. Substance is a technical term in philosophy, but its philosophical meaning is merely a more consistent development of its {187} popular meaning. In common talk, we generally apply the word substance to material things such as iron, brass, wood, or water. And we say that these substances possess qualities. For example, hardness and shininess are qualities of the substance iron. The qualities cannot exist apart from the substances. They do not exist on their own account, but are dependent on the substance. The shininess cannot exist by itself. There must be a shiny something. But, according to popular ideas, though the qualities are not independent of the substance, the substance is independent of the qualities. The qualities derive their reality from the substance. But the substance has reality in itself. The philosophical use of the term substance is simply a more consistent application of this idea. Substance means, for the philosopher, that which has its whole being in itself, whose reality does not flow into it from anything else, but which is the source of its own reality. It is self-caused, and self-determined. It is the ground of other things, but itself has no ground except itself. For example, if we believe the popular Christian idea that God created the world, but is Himself an ultimate and uncreated being, then, since the world depends for its existence upon God, but God's existence depends only upon Himself, God is a substance and the world is not. In this sense the word is correctly used in the Creed where it speaks of God as "three persons, but one substance." Again, if, with the Idealists, we think that mind is a self-existent reality, and that matter owes its existence to mind, then in that case matter is not substance, but mind is. In this technical sense the Ideas are substances. They are absolute and ultimate realities. {188} Their whole being is in themselves. They depend on nothing, but all things depend on them. They are the first principles of the universe.

Secondly, the Ideas are universal. An Idea is not any particular thing. The Idea of the horse is not this or that horse. It is the general concept of all horses. It is the universal horse. For this reason the Ideas are, in modern times, often called "universals."

Thirdly, the Ideas are not things, but thoughts. There is no such thing as the horse-in-general. If there were, we should be able to find it somewhere, and it would then be a particular thing instead of a universal. But in saying that the Ideas are thoughts, there are two mistakes to be carefully avoided. The first is to suppose that they are the thoughts of a person, that they are your thoughts or my thoughts. The second is to suppose that they are thoughts in the mind of God. Both these views are wrong. It would be absurd to suppose that our thoughts can be the cause of the universe. Our concepts are indeed copies of the Ideas, but to confuse them with the Ideas themselves is, for Plato, as absurd as to confuse our idea of a mountain with the mountain itself. Nor are they the thoughts of God. They are indeed sometimes spoken of as the "Ideas in the divine mind." But this is only a figurative expression. We can, if we like, talk of the sum of all the Ideas as constituting the "divine mind." But this means nothing in particular, and is only a poetical phrase. Both these mistakes are due to the fact that we find it difficult to conceive of thoughts without a thinker. This, however, is just what Plato meant. They are not subjective ideas, that is, the ideas in a particular and existent {189} mind. They are objective Ideas, thoughts which have reality on their own account, independently of any mind.

Fourthly, each Idea is a unity. It is the one amid the many. The Idea of man is one, although individual men are many. There cannot be more than one Idea for each class of objects. If there were several Ideas of justice, we should have to seek for the common element among them, and this common element would itself constitute the one Idea of justice.

Fifthly, the Ideas are immutable and imperishable. A concept is the same as a definition. And the whole point in a definition is that it should always be the same. The object of a definition is to compare individual things with it, and to see whether they agree with it or not. But if the definition of a triangle differed from day to day, it would be useless, since we could never say whether any particular figure were a triangle or not, just as the standard yard in the Tower of London would be useless if it changed in length, and were twice as long to-day as it was yesterday. A definition is thus something absolutely permanent, and a definition is only the expression in words of the nature of an Idea. Consequently the Ideas cannot change. The many beautiful objects arise and pass away, but the one Beauty neither begins nor ends. It is eternal, unchangeable, and imperishable. The many beautiful things are but the fleeting expressions of the one eternal beauty. The definition of man would remain the same, even if all men were destroyed. The Idea of man is eternal, and remains untouched by the birth, old age, decay, and death, of individual men.

Sixthly, the Ideas are the Essences of all things. The definition gives us what is essential to a thing. If we {190} define man as a rational animal, this means that reason is of the essence of man. The fact that this man has a turned-up nose, and that man red hair, are accidental facts, not essential to their humanity. We do not include them in the definition of man.

Seventhly, each Idea is, in its own kind, an absolute perfection, and its perfection is the same as its reality. The perfect man is the one universal type-man, that is, the Idea of man, and all individual men deviate more or less from this perfect type. In so far as they fall short of it, they are imperfect and unreal.

Eighthly, the Ideas are outside space and time. That they are outside space is obvious. If they were in space, they would have to be in some particular place. We ought to be able to find them somewhere. A telescope or microscope might reveal them. And this would mean that they are individual and particular things, and not universals at all. They are also outside time. For they are unchangeable and eternal; and this does not mean that they are the same at all times. If that were so, their immutability would be a matter of experience, and not of reason. We should, so to speak, have to look at them from time to time to see that they had not really changed. But their immutability is not a matter of experience, but is known to thought. It is not merely that they are always the same in time, but that time is irrelevant to them. They are timeless. In the "Timaeus" eternity is distinguished from infinite time. The latter is described as a mere copy of eternity.

Ninthly, the Ideas are rational, that is to say, they are apprehended through reason. The finding of the common element in the manifold is the work of inductive {191} reason, and through this alone is knowledge of the Ideas possible. This should be noted by those persons who imagine that Plato was some sort of benevolent mystic. The imperishable One, the absolute reality, is apprehended, not by intuition, or in any kind of mystic ecstasy, but only by rational cognition and laborious thought.

Lastly, towards the end of his life, Plato identified the Ideas with the Pythagorean numbers. We know this from Aristotle, but it is not mentioned in the dialogues of Plato himself. It appears to have been a theory adopted in old age, and set forth in the lectures which Aristotle attended. It is a retrograde step, and tends to degrade the great and lucid idealism of Plato into a mathematical mysticism. In this, as in other respects, the influence of the Pythagoreans upon Plato was harmful.

It results from this whole theory of Ideas that there are two sources of human experience, sense-perception and reason. Sense-perception has for its object the world of sense; reason has for its object the Ideas. The world of sense has all the opposite characteristics to the Ideas. The Ideas are absolute reality, absolute Being. Objects of sense are absolute unreality, not-being, except in so far as the Ideas are in them. Whatever reality they have they owe to the Ideas. There is in Plato's system a principle of absolute not-being which we shall consider when we come to deal with his Physics. Objects of sense participate both in the Ideas and in this not-being. They are, therefore, half way between Being and not-being. They are half real. Ideas, again, are universal; things of sense are always particular and individual. The Idea is one, the sense-object is always {192} a multiplicity. Ideas are outside space and time, things of sense are both temporal and spatial. The Idea is eternal and immutable; sense-objects are changeable and in perpetual flux.

As regards the last point, Plato adopts the view of Heracleitus that there is an absolute Becoming, and he identifies it with the world of sense, which contains nothing stable and permanent, but is a constant flow. The Idea always is, and never becomes; the thing of sense always becomes, and never is. It is for this reason that, in the opinion of Plato, no knowledge of the world of sense is possible, for one can have no knowledge of that which changes from moment to moment. Knowledge is only possible if its subject stands fixed before the mind, is permanent and changeless. The only knowledge, then, is knowledge of the Ideas.

This may seem, at first sight, a very singular doctrine. That there can be no knowledge of sense-objects would, it might seem to us moderns, involve the denial that modern physical science, with all its exactitude and accumulated knowledge, is knowledge at all. And surely, though all earthly things arise and pass away, many of them last long enough to admit of knowledge. Surely the mountains are sufficiently permanent to allow us to know something of them. They have relative, though not absolute, permanence. This criticism is partly justified. Plato did underestimate the value of physical knowledge. But for the most part, the criticism is a misunderstanding. By the world of sense Plato means bare sensation with no rational element in it. Now physical science has not such crude sensation for its object. Its objects are rationalized sensations. {193} If, in Plato's manner, we think only of pure sensation, then it is true that it is nothing but a constant flux without stability; and knowledge of it is impossible. The mountains are comparatively permanent. But our sensation of the mountains is perpetually changing. Every change of light, every cloud that passes over the sun, changes the colours and the shades. Every time we move from one situation to another, the mountain appears a different shape. The permanence of the mountain itself is due to the fact that all these varying sensations are identified as sensations of one and the same object. The idea of identity is involved here, and it is, as it were, a thread upon which these fleeting sensations are strung. But the idea of identity cannot be obtained from the senses. It is introduced into things by reason. Hence knowledge of this permanent mountain is only possible through the exercise of reason. In Plato's language, all we can know of the mountain is the Ideas in which it participates. To revert to a previous example, even the knowledge "this paper is white" involves the activity of intellect, and is impossible through sensation alone. Bare sensation is a flow, of which no knowledge is possible.

Aristotle observes that Plato's theory of Ideas has three sources, the teachings of the Eleatics, of Heracleitus, and of Socrates. From Heracleitus, Plato took the notion of a sphere of Becoming, and it appears in his system as the world of sense. From the Eleatics he took the idea of a sphere of absolute Being. From Socrates he took the doctrine of concepts, and proceeded to identify the Eleatic Being with the Socratic concepts. This gives him his theory of Ideas.

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