Plato’s Theory of Ideas

Plato's doctrine of ideas has attained an imaginary clearness and definiteness which is not to be found in his own writings. The popular account of them is partly derived from one or two passages in his Dialogues interpreted without regard to their poetical environment. It is due also to the misunderstanding of him by the Aristotelian school; and the erroneous notion has been further narrowed and has become fixed by the realism of the schoolmen. This popular view of the Platonic ideas may be summed up in some such formula as the following: 'Truth consists not in particulars, but in universals, which have a place in the mind of God, or in some far-off heaven. These were revealed to men in a former state of existence, and are recovered by reminiscence (anamnesis) or association from sensible things. The sensible things are not realities, but shadows only, in relation to the truth.' These unmeaning propositions are hardly suspected to be a caricature of a great theory of knowledge, which Plato in various ways and under many figures of speech is seeking to unfold. Poetry has been converted into dogma; and it is not remarked that the Platonic ideas are to be found only in about a third of Plato's writings and are not confined to him. The forms which they assume are numerous, and if taken literally, inconsistent with one another. At one time we are in the clouds of mythology, at another among the abstractions of mathematics or metaphysics; we pass imperceptibly from one to the other. Reason and fancy are mingled in the same passage. The ideas are sometimes described as many, coextensive with the universals of sense and also with the first principles of ethics; or again they are absorbed into the single idea of good, and subordinated to it. They are not more certain than facts, but they are equally certain (Phaedo). They are both personal and impersonal. They are abstract terms: they are also the causes of things; and they are even transformed into the demons or spirits by whose help God made the world. And the idea of good (Republic) may without violence be converted into the Supreme Being, who 'because He was good' created all things (Tim.).

Plato's doctrine of ideas has acquired a supposed clarity and precision that his own writings do not contain. The popular account comes partly from one or two passages in his Dialogues, read without regard to their poetic context. It also comes from the Aristotelian school's misunderstanding of Plato. The realism of the medieval schoolmen further narrowed this mistaken view and made it fixed. The popular view of the Platonic ideas can be summed up in something like this formula: 'Truth lies not in particular things, but in universals. These universals exist in the mind of God, or in some distant heaven. They were revealed to humans in a previous existence. People recover them through recollection (anamnesis) or through associations prompted by things perceived through the senses. These things are not realities, but only shadows in relation to the truth.' Hardly anyone suspects that these meaningless claims caricature a great theory of knowledge. Plato tries to develop that theory in various ways and through many figures of speech. Poetry has been turned into dogma. And people overlook that Platonic ideas appear in only about a third of Plato's writings and are not unique to him. The ideas take many forms that, if read literally, contradict one another. At one moment we are in the clouds of mythology, at another among the abstractions of mathematics or metaphysics. We move from one to the other without noticing. Reason and imagination mingle in the same passage. Sometimes the ideas are described as many. They cover the same range as universals drawn from sensory experience and also the first principles of ethics. At other times, the ideas merge into the single idea of good and become subordinate to it. The ideas are no more certain than facts, but they are equally certain (Phaedo). They are both personal and impersonal. They are abstract terms, but they are also the causes of things. They even become the demons or spirits whose help God used to make the world. And the idea of good (Republic) can, without distorting its meaning, become the Supreme Being. This is the being who 'because He was good' created all things (Tim.).

It would be a mistake to try and reconcile these differing modes of thought. They are not to be regarded seriously as having a distinct meaning. They are parables, prophecies, myths, symbols, revelations, aspirations after an unknown world. They derive their origin from a deep religious and contemplative feeling, and also from an observation of curious mental phenomena. They gather up the elements of the previous philosophies, which they put together in a new form. Their great diversity shows the tentative character of early endeavours to think. They have not yet settled down into a single system. Plato uses them, though he also criticises them; he acknowledges that both he and others are always talking about them, especially about the Idea of Good; and that they are not peculiar to himself (Phaedo; Republic; Soph.). But in his later writings he seems to have laid aside the old forms of them. As he proceeds he makes for himself new modes of expression more akin to the Aristotelian logic.

It would be a mistake to try to reconcile these different ways of thinking. They should not be taken seriously as having a definite meaning. They are parables, prophecies, myths, symbols, revelations, and longings for an unknown world. They come from deep religious and reflective feeling, and also from observing curious mental phenomena. They bring together elements of earlier philosophies in a new form. Their great variety shows how tentative early attempts at thinking were. These ways of thinking have not yet settled into a single system. Plato uses them, although he also criticizes them. He admits that he and others are always discussing them, especially the Idea of Good. He also acknowledges that these ways of thinking are not unique to him (Phaedo, Republic, Soph.). But in his later writings, he seems to have set aside their old forms. As he goes on, he develops new ways of expressing himself that are closer to Aristotelian logic.

Yet amid all these varieties and incongruities, there is a common meaning or spirit which pervades his writings, both those in which he treats of the ideas and those in which he is silent about them. This is the spirit of idealism, which in the history of philosophy has had many names and taken many forms, and has in a measure influenced those who seemed to be most averse to it. It has often been charged with inconsistency and fancifulness, and yet has had an elevating effect on human nature, and has exercised a wonderful charm and interest over a few spirits who have been lost in the thought of it. It has been banished again and again, but has always returned. It has attempted to leave the earth and soar heavenwards, but soon has found that only in experience could any solid foundation of knowledge be laid. It has degenerated into pantheism, but has again emerged. No other knowledge has given an equal stimulus to the mind. It is the science of sciences, which are also ideas, and under either aspect require to be defined. They can only be thought of in due proportion when conceived in relation to one another. They are the glasses through which the kingdoms of science are seen, but at a distance. All the greatest minds, except when living in an age of reaction against them, have unconsciously fallen under their power.

Yet despite all these differences and inconsistencies, a common meaning or spirit runs through his writings. It appears both where he discusses ideas and where he says nothing about them. This is the spirit of idealism. Throughout philosophy’s history, idealism has had many names and taken many forms. It has even influenced, to some extent, those who seemed most opposed to it. Idealism has often been accused of inconsistency and wild speculation. Yet it has uplifted human nature. It has also deeply fascinated a few minds absorbed in contemplating it. Idealism has been banished again and again, but it has always returned. It has tried to leave the earth and soar toward heaven. But it has soon discovered that knowledge could have a solid foundation only in experience. It has declined into pantheism, but has emerged again. No other kind of knowledge has stimulated the mind as much. Idealism is the science of sciences. The sciences are also ideas, and whether viewed as sciences or ideas, they need to be defined. Their proper proportions can be understood only when they are considered in relation to one another. Ideas are the lenses through which we see the realms of science, though from a distance. All the greatest minds have unconsciously come under the power of ideas, except during periods of reaction against them.

The account of the Platonic ideas in the Meno is the simplest and clearest, and we shall best illustrate their nature by giving this first and then comparing the manner in which they are described elsewhere, e.g. in the Phaedrus, Phaedo, Republic; to which may be added the criticism of them in the Parmenides, the personal form which is attributed to them in the Timaeus, the logical character which they assume in the Sophist and Philebus, and the allusion to them in the Laws. In the Cratylus they dawn upon him with the freshness of a newly-discovered thought.

The Meno gives the simplest and clearest account of the Platonic ideas. We can best explain their nature by presenting this account first, then comparing descriptions elsewhere. These include the Phaedrus, Phaedo, and Republic. We may also consider the criticism of the ideas in the Parmenides and their personal form in the Timaeus. Further examples include their logical character in the Sophist and Philebus, and the reference to them in the Laws. In the Cratylus, the ideas dawn on Plato with the freshness of a newly discovered thought.

The Meno goes back to a former state of existence, in which men did and suffered good and evil, and received the reward or punishment of them until their sin was purged away and they were allowed to return to earth. This is a tradition of the olden time, to which priests and poets bear witness. The souls of men returning to earth bring back a latent memory of ideas, which were known to them in a former state. The recollection is awakened into life and consciousness by the sight of the things which resemble them on earth. The soul evidently possesses such innate ideas before she has had time to acquire them. This is proved by an experiment tried on one of Meno's slaves, from whom Socrates elicits truths of arithmetic and geometry, which he had never learned in this world. He must therefore have brought them with him from another.

The Meno looks back to a previous existence, when people did and experienced good and evil. They received rewards or punishments until their sins were cleansed and they were allowed to return to earth. This is an ancient tradition, supported by priests and poets. Human souls returning to earth bring back a hidden memory of ideas they knew in a previous existence. Seeing things on earth that resemble those ideas brings the memory to life and into conscious awareness. The soul clearly possesses these inborn ideas before having time to acquire them. An experiment with one of Meno's slaves proves this. Socrates draws out from the slave truths of arithmetic and geometry that the slave had never learned in this world. The slave must therefore have brought those truths with him from another world.

The notion of a previous state of existence is found in the verses of Empedocles and in the fragments of Heracleitus. It was the natural answer to two questions, 'Whence came the soul? What is the origin of evil?' and prevailed far and wide in the east. It found its way into Hellas probably through the medium of Orphic and Pythagorean rites and mysteries. It was easier to think of a former than of a future life, because such a life has really existed for the race though not for the individual, and all men come into the world, if not 'trailing clouds of glory,' at any rate able to enter into the inheritance of the past. In the Phaedrus, as well as in the Meno, it is this former rather than a future life on which Plato is disposed to dwell. There the Gods, and men following in their train, go forth to contemplate the heavens, and are borne round in the revolutions of them. There they see the divine forms of justice, temperance, and the like, in their unchangeable beauty, but not without an effort more than human. The soul of man is likened to a charioteer and two steeds, one mortal, the other immortal. The charioteer and the mortal steed are in fierce conflict; at length the animal principle is finally overpowered, though not extinguished, by the combined energies of the passionate and rational elements. This is one of those passages in Plato which, partaking both of a philosophical and poetical character, is necessarily indistinct and inconsistent. The magnificent figure under which the nature of the soul is described has not much to do with the popular doctrine of the ideas. Yet there is one little trait in the description which shows that they are present to Plato's mind, namely, the remark that the soul, which had seen truths in the form of the universal, cannot again return to the nature of an animal.

The idea of a previous existence appears in the verses of Empedocles and the surviving fragments of Heracleitus. It was the natural answer to two questions: 'Where did the soul come from? What is the origin of evil?' This belief was widespread in the east. It probably reached Hellas through Orphic and Pythagorean rites and mysteries. A past life was easier to imagine than a future one. This was because humanity really has had a past life, though the individual has not. And all people enter the world able to inherit the past, even if they are not 'trailing clouds of glory.' In the Phaedrus, as in the Meno, Plato tends to dwell on this former life rather than a future one. In the Phaedrus, the Gods set out to contemplate the heavens, with humans following behind them. Both are carried along as the heavens revolve. There they see the divine forms of justice, temperance, and similar qualities in their unchanging beauty. But seeing these forms requires more than human effort. The human soul is compared to a charioteer with two horses, one mortal and the other immortal. The charioteer and the mortal horse struggle fiercely. Eventually, the passionate and rational elements combine their strength to overpower the animal element, though they do not destroy it. This passage, like others in Plato, combines philosophy and poetry, and so is necessarily unclear and inconsistent. The magnificent image used to describe the soul's nature has little to do with the familiar doctrine of ideas. Yet one small detail shows that Plato has that doctrine in mind. He remarks that a soul that has seen truths in their universal form cannot return to an animal's nature.

In the Phaedo, as in the Meno, the origin of ideas is sought for in a previous state of existence. There was no time when they could have been acquired in this life, and therefore they must have been recovered from another. The process of recovery is no other than the ordinary law of association, by which in daily life the sight of one thing or person recalls another to our minds, and by which in scientific enquiry from any part of knowledge we may be led on to infer the whole. It is also argued that ideas, or rather ideals, must be derived from a previous state of existence because they are more perfect than the sensible forms of them which are given by experience. But in the Phaedo the doctrine of ideas is subordinate to the proof of the immortality of the soul. 'If the soul existed in a previous state, then it will exist in a future state, for a law of alternation pervades all things.' And, 'If the ideas exist, then the soul exists; if not, not.' It is to be observed, both in the Meno and the Phaedo, that Socrates expresses himself with diffidence. He speaks in the Phaedo of the words with which he has comforted himself and his friends, and will not be too confident that the description which he has given of the soul and her mansions is exactly true, but he 'ventures to think that something of the kind is true.' And in the Meno, after dwelling upon the immortality of the soul, he adds, 'Of some things which I have said I am not altogether confident' (compare Apology; Gorgias). From this class of uncertainties he exempts the difference between truth and appearance, of which he is absolutely convinced.

In the Phaedo, as in the Meno, the origin of ideas is traced to a previous existence. There was no time when these ideas could have been acquired in this life. They must therefore have been recovered from another life. This recovery is simply the ordinary process of association. In daily life, seeing one thing or person brings another to mind. In scientific inquiry, the same process may lead us from any part of knowledge to infer the whole. Another argument holds that ideas, or rather ideals, must come from a previous existence. This is because ideals are more perfect than the forms we perceive through the senses and encounter through experience. But in the Phaedo, the theory of ideas serves the argument proving the soul’s immortality. 'If the soul existed in a previous state, then it will exist in a future state. For a law of alternation runs through all things.' And, 'If the ideas exist, then the soul exists. If not, not.' We should note that Socrates speaks cautiously in both the Meno and the Phaedo. In the Phaedo, he speaks of the words he has used to comfort himself and his friends. He is not too confident that his description of the soul and its dwelling places is exactly true. But he 'ventures to think that something of the kind is true.' And in the Meno, after discussing the soul’s immortality at length, he adds, 'I am not entirely confident about some things I have said' (compare Apology and Gorgias). But he does not include the distinction between truth and appearance among these uncertainties. Of that distinction, he is absolutely convinced.

In the Republic the ideas are spoken of in two ways, which though not contradictory are different. In the tenth book they are represented as the genera or general ideas under which individuals having a common name are contained. For example, there is the bed which the carpenter makes, the picture of the bed which is drawn by the painter, the bed existing in nature of which God is the author. Of the latter all visible beds are only the shadows or reflections. This and similar illustrations or explanations are put forth, not for their own sake, or as an exposition of Plato's theory of ideas, but with a view of showing that poetry and the mimetic arts are concerned with an inferior part of the soul and a lower kind of knowledge. On the other hand, in the 6th and 7th books of the Republic we reach the highest and most perfect conception, which Plato is able to attain, of the nature of knowledge. The ideas are now finally seen to be one as well as many, causes as well as ideas, and to have a unity which is the idea of good and the cause of all the rest. They seem, however, to have lost their first aspect of universals under which individuals are contained, and to have been converted into forms of another kind, which are inconsistently regarded from the one side as images or ideals of justice, temperance, holiness and the like; from the other as hypotheses, or mathematical truths or principles.

In the Republic, ideas are described in two different but not contradictory ways. In the tenth book, ideas are presented as categories or general ideas covering individual things with a common name. For example, there is the bed a carpenter makes, the picture of a bed a painter draws, and the bed existing in nature. God is the maker of this last bed. All visible beds are only shadows or reflections of that bed. This example and similar explanations are not offered for their own sake or to explain Plato's theory of ideas. Instead, their purpose is to show that poetry and the imitative arts involve an inferior part of the soul. These arts also involve a lower kind of knowledge. By contrast, in the sixth and seventh books of the Republic, we reach Plato's highest and most complete understanding of knowledge. Ideas are now finally seen as both one and many, and as causes as well as ideas. Their unity is the idea of good, which is also the cause of all the other ideas. Yet ideas seem to have lost their original character as universals covering individual things. They seem instead to have become forms of another kind, viewed in inconsistent ways. On one side, these forms are images or ideals of justice, temperance, holiness, and similar qualities. On the other, these forms are hypotheses, mathematical truths, or principles.

In the Timaeus, which in the series of Plato's works immediately follows the Republic, though probably written some time afterwards, no mention occurs of the doctrine of ideas. Geometrical forms and arithmetical ratios furnish the laws according to which the world is created. But though the conception of the ideas as genera or species is forgotten or laid aside, the distinction of the visible and intellectual is as firmly maintained as ever. The IDEA of good likewise disappears and is superseded by the conception of a personal God, who works according to a final cause or principle of goodness which he himself is. No doubt is expressed by Plato, either in the Timaeus or in any other dialogue, of the truths which he conceives to be the first and highest. It is not the existence of God or the idea of good which he approaches in a tentative or hesitating manner, but the investigations of physiology. These he regards, not seriously, as a part of philosophy, but as an innocent recreation (Tim.).

In the sequence of Plato's works, the Timaeus immediately follows the Republic, though it was probably written some time later. The Timaeus makes no mention of the doctrine of ideas. Geometric forms and numerical ratios provide the laws governing the world's creation. But although ideas as genera or species are forgotten or set aside, the distinction between the visible and the intelligible remains just as firm. The IDEA of good also disappears, replaced by the conception of a personal God. God works toward an ultimate purpose or principle of goodness, and he himself is that principle. Neither in the Timaeus nor in any other dialogue does Plato doubt the truths he considers first and highest. He is not tentative or hesitant about the existence of God or the idea of good. Rather, his uncertainty concerns investigations into nature. He treats these investigations not as a serious part of philosophy, but as a harmless recreation (Tim.).

Passing on to the Parmenides, we find in that dialogue not an exposition or defence of the doctrine of ideas, but an assault upon them, which is put into the mouth of the veteran Parmenides, and might be ascribed to Aristotle himself, or to one of his disciples. The doctrine which is assailed takes two or three forms, but fails in any of them to escape the dialectical difficulties which are urged against it. It is admitted that there are ideas of all things, but the manner in which individuals partake of them, whether of the whole or of the part, and in which they become like them, or how ideas can be either within or without the sphere of human knowledge, or how the human and divine can have any relation to each other, is held to be incapable of explanation. And yet, if there are no universal ideas, what becomes of philosophy? (Parmenides.) In the Sophist the theory of ideas is spoken of as a doctrine held not by Plato, but by another sect of philosophers, called 'the Friends of Ideas,' probably the Megarians, who were very distinct from him, if not opposed to him (Sophist). Nor in what may be termed Plato's abridgement of the history of philosophy (Soph.), is any mention made such as we find in the first book of Aristotle's Metaphysics, of the derivation of such a theory or of any part of it from the Pythagoreans, the Eleatics, the Heracleiteans, or even from Socrates. In the Philebus, probably one of the latest of the Platonic Dialogues, the conception of a personal or semi-personal deity expressed under the figure of mind, the king of all, who is also the cause, is retained. The one and many of the Phaedrus and Theaetetus is still working in the mind of Plato, and the correlation of ideas, not of 'all with all,' but of 'some with some,' is asserted and explained. But they are spoken of in a different manner, and are not supposed to be recovered from a former state of existence. The metaphysical conception of truth passes into a psychological one, which is continued in the Laws, and is the final form of the Platonic philosophy, so far as can be gathered from his own writings (see especially Laws). In the Laws he harps once more on the old string, and returns to general notions:—these he acknowledges to be many, and yet he insists that they are also one. The guardian must be made to recognize the truth, for which he has contended long ago in the Protagoras, that the virtues are four, but they are also in some sense one (Laws; compare Protagoras).

Turning to the Parmenides, we find no explanation or defense of the doctrine of ideas, but an attack on it. Plato puts this attack in the mouth of the veteran Parmenides. It could have come from Aristotle himself or one of his disciples. The doctrine under attack takes two or three forms. But none escapes the difficulties raised against it through logical argument. The existence of ideas of all things is accepted. Yet how individual things share in these ideas, whether wholly or partly, is considered impossible to explain. So is how individual things become like the ideas. Nor can anyone explain how ideas can fall either within or beyond human knowledge. The same difficulty applies to any relationship between the human and the divine. And yet, if there are no universal ideas, what becomes of philosophy? (Parmenides.) In the Sophist, the theory of ideas is presented as the doctrine of another school of philosophers, not Plato's. These philosophers are called 'the Friends of Ideas.' They were probably the Megarians, who were quite distinct from Plato, if not opposed to him (Sophist). The dialogue also offers what might be called Plato's brief history of philosophy (Soph.). Yet this account says nothing about the theory, or any part of it, coming from earlier thinkers. These include the Pythagoreans, the Eleatics, the Heracleiteans, and even Socrates. Such an account of the theory's origins appears in the first book of Aristotle's Metaphysics. The Philebus, probably one of Plato's latest Dialogues, retains the conception of a personal or semi-personal deity. This deity is represented as mind, the king of all, who is also the cause. The problem of the one and the many, found in the Phaedrus and Theaetetus, still occupies Plato's mind. He also asserts and explains relationships among ideas, not of 'all with all,' but of 'some with some.' But the ideas are discussed differently, and are not thought to be recovered from a previous existence. The metaphysical conception of truth becomes a psychological one. This psychological conception continues in the Laws. It is the final form of Plato's philosophy, as far as his own writings reveal (see especially Laws). In the Laws, Plato takes up his old theme once more and returns to general concepts. He acknowledges that these concepts are many, yet insists that they are also one. The guardian must be taught to recognize a truth Plato argued for long before in the Protagoras. The virtues are four, but they are also, in some sense, one (Laws, compare Protagoras).

So various, and if regarded on the surface only, inconsistent, are the statements of Plato respecting the doctrine of ideas. If we attempted to harmonize or to combine them, we should make out of them, not a system, but the caricature of a system. They are the ever-varying expression of Plato's Idealism. The terms used in them are in their substance and general meaning the same, although they seem to be different. They pass from the subject to the object, from earth (diesseits) to heaven (jenseits) without regard to the gulf which later theology and philosophy have made between them. They are also intended to supplement or explain each other. They relate to a subject of which Plato himself would have said that 'he was not confident of the precise form of his own statements, but was strong in the belief that something of the kind was true.' It is the spirit, not the letter, in which they agree—the spirit which places the divine above the human, the spiritual above the material, the one above the many, the mind before the body.

Plato’s statements about the doctrine of ideas are varied and, if viewed only on the surface, inconsistent. If we tried to reconcile or combine them, we would produce not a system but a caricature of one. These statements are the ever-changing expression of Plato’s Idealism. Their terms have the same substance and general meaning, although they seem different. The statements move from subject to object, from earth (diesseits) to heaven (jenseits). They do so without regard for the gulf that later theology and philosophy have created between these realms. The statements are also meant to supplement or explain one another. They concern a subject about which Plato himself would have said that 'he was unsure of his exact wording, but firmly believed that something of the kind was true.' The statements agree in spirit, not in their exact wording. That spirit places the divine above the human, the spiritual above the material, the one above the many, and mind before body.

The stream of ancient philosophy in the Alexandrian and Roman times widens into a lake or sea, and then disappears underground to reappear after many ages in a distant land. It begins to flow again under new conditions, at first confined between high and narrow banks, but finally spreading over the continent of Europe. It is and is not the same with ancient philosophy. There is a great deal in modern philosophy which is inspired by ancient. There is much in ancient philosophy which was 'born out of due time; and before men were capable of understanding it. To the fathers of modern philosophy, their own thoughts appeared to be new and original, but they carried with them an echo or shadow of the past, coming back by recollection from an elder world. Of this the enquirers of the seventeenth century, who to themselves appeared to be working out independently the enquiry into all truth, were unconscious. They stood in a new relation to theology and natural philosophy, and for a time maintained towards both an attitude of reserve and separation. Yet the similarities between modern and ancient thought are greater far than the differences. All philosophy, even that part of it which is said to be based upon experience, is really ideal; and ideas are not only derived from facts, but they are also prior to them and extend far beyond them, just as the mind is prior to the senses.

In Alexandrian and Roman times, the stream of ancient philosophy widens into a lake or sea, then disappears underground. Many ages later, the stream reappears in a distant land. Philosophy begins to flow again under new conditions, at first confined between high, narrow banks. Eventually, it spreads across the continent of Europe. This philosophy is both the same as ancient philosophy and different from it. Much in modern philosophy is inspired by ancient thought. Much in ancient philosophy was 'born before its time', before people could understand it. To the founders of modern philosophy, their own thoughts seemed new and original. Yet those thoughts carried an echo or shadow of the past, recalled from an older world. The thinkers of the seventeenth century were unaware of this connection to the past. They believed they were independently pursuing an inquiry into all truth. Their relationship with theology and natural philosophy, the study of nature, was new. For a time, they remained guarded toward both fields and kept their distance from them. Yet the similarities between modern and ancient thought far outweigh the differences. All philosophy, even the philosophy said to rest on experience, is really grounded in ideas. Ideas do not simply come from facts. Ideas also come before facts and reach far beyond them, just as the mind comes before the senses.

Early Greek speculation culminates in the ideas of Plato, or rather in the single idea of good. His followers, and perhaps he himself, having arrived at this elevation, instead of going forwards went backwards from philosophy to psychology, from ideas to numbers. But what we perceive to be the real meaning of them, an explanation of the nature and origin of knowledge, will always continue to be one of the first problems of philosophy.

Early Greek thought reaches its peak in Plato’s ideas, or rather in the single idea of good. His followers, and perhaps Plato himself, reached this height but then moved backward instead of forward. They moved from philosophy to psychology, from ideas to numbers. But we see the real meaning of these ideas as an explanation of the nature and origin of knowledge. That explanation will always remain one of philosophy’s central problems.

Plato also left behind him a most potent instrument, the forms of logic—arms ready for use, but not yet taken out of their armoury. They were the late birth of the early Greek philosophy, and were the only part of it which has had an uninterrupted hold on the mind of Europe. Philosophies come and go; but the detection of fallacies, the framing of definitions, the invention of methods still continue to be the main elements of the reasoning process.

Plato also left behind a powerful tool: the forms of logic. These were weapons ready for use, but not yet taken from the armory. These forms emerged late in early Greek philosophy. They were the only part of that philosophy to maintain an unbroken hold on the European mind. Philosophies come and go. But identifying faulty arguments, creating definitions, and developing methods remain the main elements of reasoning.

Modern philosophy, like ancient, begins with very simple conceptions. It is almost wholly a reflection on self. It might be described as a quickening into life of old words and notions latent in the semi-barbarous Latin, and putting a new meaning into them. Unlike ancient philosophy, it has been unaffected by impressions derived from outward nature: it arose within the limits of the mind itself. From the time of Descartes to Hume and Kant it has had little or nothing to do with facts of science. On the other hand, the ancient and mediaeval logic retained a continuous influence over it, and a form like that of mathematics was easily impressed upon it; the principle of ancient philosophy which is most apparent in it is scepticism; we must doubt nearly every traditional or received notion, that we may hold fast one or two. The being of God in a personal or impersonal form was a mental necessity to the first thinkers of modern times: from this alone all other ideas could be deduced. There had been an obscure presentiment of 'cognito, ergo sum' more than 2000 years previously. The Eleatic notion that being and thought were the same was revived in a new form by Descartes. But now it gave birth to consciousness and self-reflection: it awakened the 'ego' in human nature. The mind naked and abstract has no other certainty but the conviction of its own existence. 'I think, therefore I am;' and this thought is God thinking in me, who has also communicated to the reason of man his own attributes of thought and extension—these are truly imparted to him because God is true (compare Republic). It has been often remarked that Descartes, having begun by dismissing all presuppositions, introduces several: he passes almost at once from scepticism to dogmatism. It is more important for the illustration of Plato to observe that he, like Plato, insists that God is true and incapable of deception (Republic)—that he proceeds from general ideas, that many elements of mathematics may be found in him. A certain influence of mathematics both on the form and substance of their philosophy is discernible in both of them. After making the greatest opposition between thought and extension, Descartes, like Plato, supposes them to be reunited for a time, not in their own nature but by a special divine act (compare Phaedrus), and he also supposes all the parts of the human body to meet in the pineal gland, that alone affording a principle of unity in the material frame of man. It is characteristic of the first period of modern philosophy, that having begun (like the Presocratics) with a few general notions, Descartes first falls absolutely under their influence, and then quickly discards them. At the same time he is less able to observe facts, because they are too much magnified by the glasses through which they are seen. The common logic says 'the greater the extension, the less the comprehension,' and we may put the same thought in another way and say of abstract or general ideas, that the greater the abstraction of them, the less are they capable of being applied to particular and concrete natures.

Modern philosophy, like ancient philosophy, begins with very simple ideas. It consists almost entirely of reflection on the self. We might describe it as bringing old words and ideas to life and giving them new meanings. These had lain dormant in a partly barbarous form of Latin. Unlike ancient philosophy, modern philosophy has been unaffected by impressions drawn from the natural world. It arose within the mind itself. From Descartes to Hume and Kant, it had little or nothing to do with scientific facts. On the other hand, ancient and medieval logic continued to influence modern philosophy. Modern philosophy also readily took on a mathematical form. The principle of ancient philosophy most apparent in modern philosophy is scepticism. We must doubt nearly every traditional or accepted idea so that we can hold firmly to one or two. For the first modern thinkers, the existence of God, whether personal or impersonal, was a mental necessity. From God's existence alone, all other ideas could be deduced. There had been a vague anticipation of 'cognito, ergo sum' more than 2,000 years earlier. Descartes revived, in a new form, the Eleatic idea that being and thought were the same. But now this idea gave rise to consciousness and self-reflection. It awakened the 'ego' in human nature. The mind, stripped of everything and considered in the abstract, has only one certainty: its conviction that it exists. 'I think, therefore I am;' and this thought is God thinking in me. God has also given human reason his own attributes of thought and extension. These attributes are genuinely given to human reason because God is truthful (compare Republic). As people have often noted, Descartes begins by rejecting all assumptions, but then introduces several. He moves almost immediately from scepticism to dogmatism. To shed light on Plato, however, it is more important to notice other features of Descartes's thought. Like Plato, Descartes insists that God is truthful and incapable of deception (Republic). Descartes also starts from general ideas, and his philosophy contains many elements of mathematics. Mathematics has a discernible influence on both the form and content of each philosopher's work. Descartes first draws the sharpest possible distinction between thought and extension. Then, like Plato, he supposes that thought and extension are reunited for a time. They are reunited not by their own nature, but through a special act of God (compare Phaedrus). Descartes also supposes that all parts of the human body meet in the pineal gland. He sees this gland alone as providing a unifying principle for the human body's material structure. Descartes begins, like the Presocratics, with a few general ideas. He first falls completely under their influence, then quickly discards them. This pattern is characteristic of the first period of modern philosophy. At the same time, he is less able to observe facts. The lenses through which he views facts magnify them too much. Traditional logic says, 'the greater the extension, the less the comprehension,' meaning that broader categories have fewer defining features. We can express the same thought another way about abstract or general ideas. The more abstract these ideas become, the less they can be applied to particular, concrete things.

Not very different from Descartes in his relation to ancient philosophy is his successor Spinoza, who lived in the following generation. The system of Spinoza is less personal and also less dualistic than that of Descartes. In this respect the difference between them is like that between Xenophanes and Parmenides. The teaching of Spinoza might be described generally as the Jewish religion reduced to an abstraction and taking the form of the Eleatic philosophy. Like Parmenides, he is overpowered and intoxicated with the idea of Being or God. The greatness of both philosophies consists in the immensity of a thought which excludes all other thoughts; their weakness is the necessary separation of this thought from actual existence and from practical life. In neither of them is there any clear opposition between the inward and outward world. The substance of Spinoza has two attributes, which alone are cognizable by man, thought and extension; these are in extreme opposition to one another, and also in inseparable identity. They may be regarded as the two aspects or expressions under which God or substance is unfolded to man. Here a step is made beyond the limits of the Eleatic philosophy. The famous theorem of Spinoza, 'Omnis determinatio est negatio,' is already contained in the 'negation is relation' of Plato's Sophist. The grand description of the philosopher in Republic VI, as the spectator of all time and all existence, may be paralleled with another famous expression of Spinoza, 'Contemplatio rerum sub specie eternitatis.' According to Spinoza finite objects are unreal, for they are conditioned by what is alien to them, and by one another. Human beings are included in the number of them. Hence there is no reality in human action and no place for right and wrong. Individuality is accident. The boasted freedom of the will is only a consciousness of necessity. Truth, he says, is the direction of the reason towards the infinite, in which all things repose; and herein lies the secret of man's well-being. In the exaltation of the reason or intellect, in the denial of the voluntariness of evil (Timaeus; Laws) Spinoza approaches nearer to Plato than in his conception of an infinite substance. As Socrates said that virtue is knowledge, so Spinoza would have maintained that knowledge alone is good, and what contributes to knowledge useful. Both are equally far from any real experience or observation of nature. And the same difficulty is found in both when we seek to apply their ideas to life and practice. There is a gulf fixed between the infinite substance and finite objects or individuals of Spinoza, just as there is between the ideas of Plato and the world of sense.

Spinoza, Descartes’s successor, lived in the next generation. His relationship to ancient philosophy was not very different from Descartes’s. Spinoza’s system is less personal and less dualistic than Descartes’s. In this respect, their difference resembles the difference between Xenophanes and Parmenides. Spinoza’s teaching might broadly be described as the Jewish religion reduced to an abstraction, taking the form of Eleatic philosophy. Like Parmenides, Spinoza is overwhelmed and intoxicated by the idea of Being or God. Both philosophies draw their greatness from the vastness of a thought that excludes all other thoughts. Their weakness is that this thought is necessarily separated from actual existence and practical life. Neither philosophy clearly sets the inner and outer worlds against each other. Spinoza’s substance has two attributes that humans alone can know: thought and extension. These attributes are completely opposed, yet inseparably identical. They may be seen as the two aspects or expressions through which God or substance is revealed to humans. This takes a step beyond the limits of Eleatic philosophy. Spinoza’s famous proposition, 'Omnis determinatio est negatio,' is already contained in 'negation is relation' in Plato’s Sophist. Republic VI grandly describes the philosopher as the spectator of all time and all existence. This description may be compared with another famous expression of Spinoza’s, 'Contemplatio rerum sub specie eternitatis.' According to Spinoza, finite objects are unreal because they are conditioned by things outside themselves and by one another. Human beings are among these finite objects. Therefore, human action has no reality, and there is no place for right and wrong. Individuality is an accidental feature. The much-praised freedom of the will is only an awareness of necessity. Truth, Spinoza says, is reason directed toward the infinite, in which all things rest. Here lies the secret of human well-being. Spinoza elevates reason or intellect and denies that evil is voluntary (Timaeus, Laws). In these respects, he comes closer to Plato than in his conception of an infinite substance. Socrates said that virtue is knowledge. Similarly, Spinoza would have maintained that knowledge alone is good, and whatever contributes to knowledge is useful. Both thinkers are equally distant from any real experience or observation of nature. Both also present the same difficulty when we try to apply their ideas to life and practice. A gulf separates Spinoza’s infinite substance from finite objects or individuals. Just such a gulf separates Plato’s ideas from the world of the senses.

Removed from Spinoza by less than a generation is the philosopher Leibnitz, who after deepening and intensifying the opposition between mind and matter, reunites them by his preconcerted harmony (compare again Phaedrus). To him all the particles of matter are living beings which reflect on one another, and in the least of them the whole is contained. Here we catch a reminiscence both of the omoiomere, or similar particles of Anaxagoras, and of the world-animal of the Timaeus.

The philosopher Leibnitz lived less than a generation after Spinoza. Leibnitz deepened and sharpened the opposition between mind and matter, then reunited them through his preconcerted harmony (compare again Phaedrus). For Leibnitz, all particles of matter are living beings that reflect one another. Even the smallest particle contains the whole. Here we find echoes of both the omoiomere, or similar particles, of Anaxagoras and the world-animal of the Timaeus.

In Bacon and Locke we have another development in which the mind of man is supposed to receive knowledge by a new method and to work by observation and experience. But we may remark that it is the idea of experience, rather than experience itself, with which the mind is filled. It is a symbol of knowledge rather than the reality which is vouchsafed to us. The Organon of Bacon is not much nearer to actual facts than the Organon of Aristotle or the Platonic idea of good. Many of the old rags and ribbons which defaced the garment of philosophy have been stripped off, but some of them still adhere. A crude conception of the ideas of Plato survives in the 'forms' of Bacon. And on the other hand, there are many passages of Plato in which the importance of the investigation of facts is as much insisted upon as by Bacon. Both are almost equally superior to the illusions of language, and are constantly crying out against them, as against other idols.

In Bacon and Locke, we find another development: the human mind is thought to gain knowledge through a new method. The mind works through observation and experience. But we may note that the mind is filled with the idea of experience, rather than experience itself. We are given a symbol of knowledge rather than knowledge itself. Bacon’s Organon is not much closer to actual facts than Aristotle’s Organon or the Platonic idea of good. Many of the old rags and ribbons that spoiled philosophy’s clothing have been stripped away. But some still cling to it. A crude version of Plato’s ideas survives in Bacon’s 'forms'. On the other hand, many passages in Plato stress the importance of investigating facts as strongly as Bacon does. Both thinkers are almost equally able to see through the illusions of language. Both constantly speak out against these illusions, as they do against other idols.

Locke cannot be truly regarded as the author of sensationalism any more than of idealism. His system is based upon experience, but with him experience includes reflection as well as sense. His analysis and construction of ideas has no foundation in fact; it is only the dialectic of the mind 'talking to herself.' The philosophy of Berkeley is but the transposition of two words. For objects of sense he would substitute sensations. He imagines himself to have changed the relation of the human mind towards God and nature; they remain the same as before, though he has drawn the imaginary line by which they are divided at a different point. He has annihilated the outward world, but it instantly reappears governed by the same laws and described under the same names.

Locke cannot truly be considered the founder of sensationalism any more than of idealism. His system rests on experience, but for him experience includes reflection as well as sensation. His analysis of ideas and his account of how ideas are formed have no basis in fact. They are only the mind’s reasoning as it is 'talking to herself.' Berkeley’s philosophy merely swaps two words. He replaces objects perceived by the senses with sensations. He imagines he has changed the human mind’s relationship with God and nature. Those relationships remain unchanged, though he has moved the imaginary line that divides the mind from God and nature. He has wiped out the external world, but that world immediately reappears, governed by the same laws and described by the same names.

A like remark applies to David Hume, of whose philosophy the central principle is the denial of the relation of cause and effect. He would deprive men of a familiar term which they can ill afford to lose; but he seems not to have observed that this alteration is merely verbal and does not in any degree affect the nature of things. Still less did he remark that he was arguing from the necessary imperfection of language against the most certain facts. And here, again, we may find a parallel with the ancients. He goes beyond facts in his scepticism, as they did in their idealism. Like the ancient Sophists, he relegates the more important principles of ethics to custom and probability. But crude and unmeaning as this philosophy is, it exercised a great influence on his successors, not unlike that which Locke exercised upon Berkeley and Berkeley upon Hume himself. All three were both sceptical and ideal in almost equal degrees. Neither they nor their predecessors had any true conception of language or of the history of philosophy. Hume's paradox has been forgotten by the world, and did not any more than the scepticism of the ancients require to be seriously refuted. Like some other philosophical paradoxes, it would have been better left to die out. It certainly could not be refuted by a philosophy such as Kant's, in which, no less than in the previously mentioned systems, the history of the human mind and the nature of language are almost wholly ignored, and the certainty of objective knowledge is transferred to the subject; while absolute truth is reduced to a figment, more abstract and narrow than Plato's ideas, of 'thing in itself,' to which, if we reason strictly, no predicate can be applied.

A similar point applies to David Hume, whose philosophy centers on denying the relationship between cause and effect. He would take away a familiar term that people can hardly afford to lose. But he seems not to have noticed that this change concerns words alone and does not affect reality at all. Still less did he notice that he was using language’s inevitable imperfections to argue against the most certain facts. Here again, we may find a parallel with ancient thinkers. His skepticism goes beyond the facts, just as their idealism did. Like the ancient Sophists, he leaves the more important principles of ethics to custom and probability. But crude and meaningless as this philosophy is, it greatly influenced his successors. Its influence resembled Locke’s influence on Berkeley and Berkeley’s on Hume himself. All three were both skeptical and idealist in almost equal measure. Neither they nor their predecessors truly understood language or the history of philosophy. The world has forgotten Hume's paradox. Like ancient skepticism, his paradox did not need to be seriously refuted. Like some other philosophical paradoxes, it would have been better left to die out. Certainly, a philosophy such as Kant's could not refute it. Like the systems already mentioned, Kant's philosophy almost entirely ignores the history of the human mind and the nature of language. It also shifts the certainty of objective knowledge to the knowing subject. Meanwhile, absolute truth becomes an imaginary concept, more abstract and narrower than Plato's ideas: the 'thing in itself'. If we reason strictly, we can attribute no quality to this 'thing in itself'.

The question which Plato has raised respecting the origin and nature of ideas belongs to the infancy of philosophy; in modern times it would no longer be asked. Their origin is only their history, so far as we know it; there can be no other. We may trace them in language, in philosophy, in mythology, in poetry, but we cannot argue a priori about them. We may attempt to shake them off, but they are always returning, and in every sphere of science and human action are tending to go beyond facts. They are thought to be innate, because they have been familiar to us all our lives, and we can no longer dismiss them from our mind. Many of them express relations of terms to which nothing exactly or nothing at all in rerum natura corresponds. We are not such free agents in the use of them as we sometimes imagine. Fixed ideas have taken the most complete possession of some thinkers who have been most determined to renounce them, and have been vehemently affirmed when they could be least explained and were incapable of proof. The world has often been led away by a word to which no distinct meaning could be attached. Abstractions such as 'authority,' 'equality,' 'utility,' 'liberty,' 'pleasure,' 'experience,' 'consciousness,' 'chance,' 'substance,' 'matter,' 'atom,' and a heap of other metaphysical and theological terms, are the source of quite as much error and illusion and have as little relation to actual facts as the ideas of Plato. Few students of theology or philosophy have sufficiently reflected how quickly the bloom of a philosophy passes away; or how hard it is for one age to understand the writings of another; or how nice a judgment is required of those who are seeking to express the philosophy of one age in the terms of another. The 'eternal truths' of which metaphysicians speak have hardly ever lasted more than a generation. In our own day schools or systems of philosophy which have once been famous have died before the founders of them. We are still, as in Plato's age, groping about for a new method more comprehensive than any of those which now prevail; and also more permanent. And we seem to see at a distance the promise of such a method, which can hardly be any other than the method of idealized experience, having roots which strike far down into the history of philosophy. It is a method which does not divorce the present from the past, or the part from the whole, or the abstract from the concrete, or theory from fact, or the divine from the human, or one science from another, but labours to connect them. Along such a road we have proceeded a few steps, sufficient, perhaps, to make us reflect on the want of method which prevails in our own day. In another age, all the branches of knowledge, whether relating to God or man or nature, will become the knowledge of 'the revelation of a single science' (Symp.), and all things, like the stars in heaven, will shed their light upon one another.

Plato’s question about the origin and nature of ideas belongs to philosophy’s infancy. In modern times, the question would no longer be asked. The origin of ideas is simply their history, as far as we know it. There can be no other origin. We may trace ideas through language, philosophy, mythology, and poetry, but we cannot reason about them independently of experience. We may try to shake ideas off, but they always return. In every field of science and human activity, ideas tend to go beyond the facts. Ideas are thought to be innate because we have known them all our lives and can no longer dismiss them. Many ideas express relationships between terms that have no exact counterpart, or no counterpart at all, in nature. We are not always as free in using ideas as we imagine. Fixed ideas have completely taken over some thinkers who were most determined to reject them. Such ideas have been passionately asserted when they were least explainable and could not be proved. The world has often been led astray by a word with no clear meaning. Consider abstractions such as 'authority,' 'equality,' 'utility,' 'liberty,' 'pleasure,' 'experience,' 'consciousness,' 'chance,' 'substance,' 'matter,' and 'atom.' These and a host of other metaphysical and theological terms cause just as much error and illusion as Plato’s ideas. They also have just as little connection to actual facts. Few students of theology or philosophy have thought enough about how quickly a philosophy loses its freshness. Few have considered how hard one age finds it to understand another age’s writings. Nor have they sufficiently considered the fine judgment needed to express one age’s philosophy in another age’s terms. The 'eternal truths' that metaphysicians speak of have hardly ever lasted more than a generation. In our own day, once-famous schools or systems of philosophy have died before their founders. As in Plato’s age, we are still feeling our way toward a new method. We seek a method broader than any now in use, and also more lasting. And we seem to see, in the distance, the promise of such a method. This can hardly be anything other than the method of idealized experience, rooted deep in the history of philosophy. This method does not separate the present from the past, the part from the whole, or the abstract from the concrete. Nor does it separate theory from fact, the divine from the human, or one science from another. Instead, the method works to connect them. We have taken a few steps along this road. Perhaps these steps are enough to make us reflect on the lack of method in our own day. In another age, all branches of knowledge, whether about God, humanity, or nature, will become one body of knowledge. This will be knowledge of 'the revelation of a single science' (Symp.). And all things, like the stars in the sky, will cast their light on one another.