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Early Readings in the Philosophy of Science

Plato (circa 427-347 BCE)

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Bust of Plato via Wikimedia Commons

One cannot study philosophy without considering Plato, perhaps the most influential philosopher of any period. Plato lived in Athens, Greece, and studied with the famous teacher Socrates, before eventually founding his own school, the Academy. Aristotle was one of his students.

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Studying with Socrates, medieval manuscript drawing

For the philosophy of science, Plato's contributions to metaphysics and the nature of reality are perhaps the most crucial. The selections below encompass some of his more famous passages on these questions. Plato argued that the world as we experience it is a flawed or imperfect version of the real world, which is composed of the perfect essence of things, often referred to as Forms or Ideas. Thus, we perceive a beautiful tree, but the tree of our perception only partakes in some small part of the essence or idea of Beauty, and the idea of Treeness.

Plato's writing takes the form of dialogues or conversations between Socrates and various students. Socrates forwards a proposition, sometimes restating it to clarify the concept, and asks the student to concur with each step of his reasoning before moving to the next phase.

The first two selections are from the Phaedo. In "Two Worlds: Forms and Senses," Socrates demonstrates the distinction between the ideal world of Forms and the flawed world of our senses. "Socrates Intellectual History" describes how Socrates moved away from observing nature with his senses and toward reasoning about nature based on his intellectual ability to comprehend the ideal forms that lie behind our observations.

The excerpts from The Republic pursue the distinction between the ideal forms and the observations mediated by sensory experience still further. In "The Analogy of the Divided Line" Plato highlights the differences between scientific knowledge, which apprehends the world through logic and mathematics, and wisdom, which apprehends the transcendent world of ideas. "The Allegory of the Cave" then provides one of Plato's most frequently cited descriptions of the difference between the world we perceive through the senses and the world as it truly is.

A note on the text: English language translations have been taken from the Perseus Digital Library under a Creative Commons CC-BY-SA license. The notations in parentheses are conventional references to sections of the text.

You can navigate throughout this chapter using the links below:

Excerpts from the Phaedo

Excerpts from The Republic

Further Reading

Excerpts from the Phaedo

Plato. Plato in Twelve Volumes, Vol. 1 translated by Harold North Fowler; Introduction by W.R.M. Lamb. Cambridge, MA, Harvard University Press; London, William Heinemann Ltd. 1966.

For a summary of the full text, see the article Plato's Phaedo in the Internet Encyclopedia of Philosophy.

Two Worlds: Forms and Senses (78b-79a)

“Is the absolute essence, which we in our dialectic process of question and answer call true being, always the same or is it liable to change? Absolute equality, absolute beauty, any absolute existence, true being—do they ever admit of any change whatsoever? Or does each absolute essence, since it is uniform and exists by itself, remain the same and never in any way admit of any change?”

“It must,” said Cebes, “necessarily remain the same, Socrates.”

“But how about the many things, for example, men, or horses, or cloaks, or any other such things, which bear the same names as the absolute essences and are called beautiful or equal or the like? Are they always the same? Or are they, in direct opposition to the essences, constantly changing in themselves, unlike each other, and, so to speak, never the same?”

“The latter,” said Cebes; “they are never the same.”

“And you can see these and touch them and perceive them by the other senses, whereas the things which are always the same can be grasped only by the reason, and are invisible and not to be seen?”

“Certainly,” said he, “that is true.”

Socrates' Intellectual History (96a-102a)

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Sketch of Socrates, William Blake [Public domain], via Wikimedia Commons

“Listen then, and I will tell you. When I was young, Cebes, I was tremendously eager for the kind of wisdom which they call investigation of nature. I thought it was a glorious thing to know the causes of everything, why each thing comes into being and why it perishes and why it exists; and I was always unsettling myself with such questions as these: Do heat and cold, by a sort of fermentation, bring about the organization of animals, as some people say? Is it the blood, or air, or fire by which we think? Or is it none of these, and does the brain furnish the sensations of hearing and sight and smell, and do memory and opinion arise from these, and does knowledge come from memory and opinion in a state of rest? And again I tried to find out how these things perish, and I investigated the phenomena of heaven and earth until finally I made up my mind that I was by nature totally unfitted for this kind of investigation. And I will give you a sufficient proof of this. I was so completely blinded by these studies that I lost the knowledge that I, and others also, thought I had before; I forgot what I had formerly believed I knew about many things and even about the cause of man's growth. For I had thought previously that it was plain to everyone that man grows through eating and drinking; for when, from the food he eats, flesh is added to his flesh and bones to his bones, and in the same way the appropriate thing is added to each of his other parts, then the small bulk becomes greater and the small man large. That is what I used to think. Doesn't that seem to you reasonable?”

“Yes,” said Cebes.

“Now listen to this, too. I thought I was sure enough, when I saw a tall man standing by a short one, that he was, say, taller by a head than the other, and that one horse was larger by a head than another horse; and, to mention still clearer things than those, I thought ten were more than eight because two had been added to the eight, and I thought a two-cubit rule was longer than a one-cubit rule because it exceeded it by half its length.”

“And now,” said Cebes, “what do you think about them?”

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Johann Friedrich Greuter: Socrates and His Students, 17th century

“By Zeus,” said he, “I am far from thinking that I know the cause of any of these things, I who do not even dare to say, when one is added to one, whether the one to which the addition was made has become two, or the one which was added, or the one which was added and the one to which it was added became two by the addition of each to the other. I think it is wonderful that when each of them was separate from the other, each was one and they were not then two, and when they were brought near each other this juxtaposition was the cause of their becoming two. And I cannot yet believe that if one is divided, the division causes it to become two; for this is the opposite of the cause which produced two in the former case; for then two arose because one was brought near and added to another one, and now because one is removed and separated from other. And I no longer believe that I know by this method even how one is generated or, in a word, how anything is generated or is destroyed or exists, and I no longer admit this method, but have another confused way of my own.

“Then one day I heard a man reading from a book, as he said, by Anaxagoras, that it is the mind that arranges and causes all things. I was pleased with this theory of cause, and it seemed to me to be somehow right that the mind should be the cause of all things, and I thought, 'If this is so, the mind in arranging things arranges everything and establishes each thing as it is best for it to be. So if anyone wishes to find the cause of the generation or destruction or existence of a particular thing, he must find out what sort of existence, or passive state of any kind, or activity is best for it. And therefore in respect to that particular thing, and other things too, a man need examine nothing but what is best and most excellent; for then he will necessarily know also what is inferior, since the science of both is the same. As I considered these things I was delighted to think that I had found in Anaxagoras a teacher of the cause of things quite to my mind, and I thought he would tell me whether the earth is flat or round, and when he had told me that, would go on to explain the cause and the necessity of it, and would tell me the nature of the best and why it is best for the earth to be as it is; and if he said the earth was in the center, he would proceed to show that it is best for it to be in the center; and I had made up my mind that if he made those things clear to me, I would no longer yearn for any other kind of cause. And I had determined that I would find out in the same way about the sun and the moon and the other stars, their relative speed, their revolutions, and their other changes, and why the active or passive condition of each of them is for the best. For I never imagined that, when he said they were ordered by intelligence, he would introduce any other cause for these things than that it is best for them to be as they are.

So I thought when he assigned the cause of each thing and of all things in common he would go on and explain what is best for each and what is good for all in common. I prized my hopes very highly, and I seized the books very eagerly and read them as fast as I could, that I might know as fast as I could about the best and the worst.

“My glorious hope, my friend, was quickly snatched away from me. As I went on with my reading I saw that the man made no use of intelligence, and did not assign any real causes for the ordering of things, but mentioned as causes air and ether and water and many other absurdities. And it seemed to me it was very much as if one should say that Socrates does with intelligence whatever he does, and then, in trying to give the causes of the particular thing I do, should say first that I am now sitting here because my body is composed of bones and sinews, and the bones are hard and have joints which divide them and the sinews can be contracted and relaxed and, with the flesh and the skin which contains them all, are laid about the bones; and so, as the bones are hung loose in their ligaments, the sinews, by relaxing and contracting, make me able to bend my limbs now, and that is the cause of my sitting here with my legs bent. Or as if in the same way he should give voice and air and hearing and countless other things of the sort as causes for our talking with each other, and should fail to mention the real causes, which are, that the Athenians decided that it was best to condemn me, and therefore I have decided that it was best for me to sit here and that it is right for me to stay and undergo whatever penalty they order.

For, by Dog, I fancy these bones and sinews of mine would have been in Megara or Boeotia long ago, carried thither by an opinion of what was best, if I did not think it was better and nobler to endure any penalty the city may inflict rather than to escape and run away. But it is most absurd to call things of that sort causes. If anyone were to say that I could not have done what I thought proper if I had not bones and sinews and other things that I have, he would be right. But to say that those things are the cause of my doing what I do, and that I act with intelligence but not from the choice of what is best, would be an extremely careless way of talking. Whoever talks in that way is unable to make a distinction and to see that in reality a cause is one thing, and the thing without which the cause could never be a cause is quite another thing. And so it seems to me that most people, when they give the name of cause to the latter, are groping in the dark, as it were, and are giving it a name that does not belong to it. And so one man makes the earth stay below the heavens by putting a vortex about it, and another regards the earth as a flat trough supported on a foundation of air; but they do not look for the power which causes things to be now placed as it is best for them to be placed, nor do they think it has any divine force, but they think they can find a new Atlas more powerful and more immortal and more all-embracing than this, and in truth they give no thought to the good, which must embrace and hold together all things. Now I would gladly be the pupil of anyone who would teach me the nature of such a cause; but since that was denied me and I was not able to discover it myself or to learn of it from anyone else, do you wish me, Cebes,” said he, “to give you an account of the way in which I have conducted my second voyage in quest of the cause?”

“I wish it with all my heart,” he replied.

“After this, then,” said he, “since I had given up investigating realities, I decided that I must be careful not to suffer the misfortune which happens to people who look at the sun and watch it during an eclipse. For some of them ruin their eyes unless they look at its image in water or something of the sort. I thought of that danger, and I was afraid my soul would be blinded if I looked at things with my eyes and tried to grasp them with any of my senses. So I thought I must have recourse to conceptions and examine in them the truth of realities. Now perhaps my metaphor is not quite accurate; for I do not grant in the least that he who studies realities by means of conceptions is looking at them in images any more than he who studies them in the facts of daily life. However, that is the way I began. I assume in each case some principle which I consider strongest, and whatever seems to me to agree with this, whether relating to cause or to anything else, I regard as true, and whatever disagrees with it, as untrue. But I want to tell you more clearly what I mean; for I think you do not understand now.”

“Not very well, certainly,” said Cebes.

“Well,” said Socrates, “this is what I mean. It is nothing new, but the same thing I have always been saying, both in our previous conversation and elsewhere. I am going to try to explain to you the nature of that cause which I have been studying, and I will revert to those familiar subjects of ours as my point of departure and assume that there are such things as absolute beauty and good and greatness and the like. If you grant this and agree that these exist, I believe I shall explain cause to you and shall prove that the soul is immortal.”

“You may assume,” said Cebes, “that I grant it, and go on.”

“Then,” said he, “see if you agree with me in the next step. I think that if anything is beautiful besides absolute beauty it is beautiful for no other reason than because it partakes of absolute beauty; and this applies to everything. Do you assent to this view of cause?”

“I do,” said he.

“Now I do not yet, understand,” he went on, “nor can I perceive those other ingenious causes. If anyone tells me that what makes a thing beautiful is its lovely color, or its shape or anything else of the sort, I let all that go, for all those things confuse me, and I hold simply and plainly and perhaps foolishly to this, that nothing else makes it beautiful but the presence or communion (call it which you please) of absolute beauty, however it may have been gained; about the way in which it happens, I make no positive statement as yet, but I do insist that beautiful things are made beautiful by beauty. For I think this is the safest answer I can give to myself or to others, and if I cleave fast to this, I think I shall never be overthrown, and I believe it is safe for me or anyone else to give this answer, that beautiful things are beautiful through beauty. Do you agree?”

“I do.”

“And great things are great and greater things greater by greatness, and smaller things smaller by smallness?”


“And you would not accept the statement, if you were told that one man was greater or smaller than another by a head, but you would insist that you say only that every greater thing is greater than another by nothing else than greatness, and that it is greater by reason of greatness, and that which is smaller is smaller by nothing else than smallness and is smaller by reason of smallness. For you would, I think, be afraid of meeting with the retort, if you said that a man was greater or smaller than another by a head, first that the greater is greater and the smaller is smaller by the same thing, and secondly, that the greater man is greater by a head, which is small, and that it is a monstrous thing that one is great by something that is small. Would you not be afraid of this?”

And Cebes laughed and said, “Yes, I should.”

“Then,” he continued, “you would be afraid to say that ten is more than eight by two and that this is the reason it is more. You would say it is more by number and by reason of number; and a two-cubit measure is greater than a one-cubit measure not by half but by magnitude, would you not? For you would have the same fear.”

“Certainly,” said he.

“Well, then, if one is added to one or if one is divided, you would avoid saying that the addition or the division is the cause of two? You would exclaim loudly that you know no other way by which any thing can come into existence than by participating in the proper essence of each thing in which it participates, and therefore you accept no other cause of the existence of two than participation in duality, and things which are to be two must participate in duality, and whatever is to be one must participate in unity, and you would pay no attention to the divisions and additions and other such subtleties, leaving those for wiser men to explain. You would distrust your inexperience and would be afraid, as the saying goes, of your own shadow; so you would cling to that safe principle of ours and would reply as I have said. And if anyone attacked the principle, you would pay him no attention and you would not reply to him until you had examined the consequences to see whether they agreed with one another or not; and when you had to give an explanation of the principle, you would give it in the same way by assuming some other principle which seemed to you the best of the higher ones, and so on until you reached one which was adequate. You would not mix things up, as disputants do, in talking about the beginning and its consequences, if you wished to discover any of the realities; for perhaps not one of them thinks or cares in the least about these things. They are so clever that they succeed in being well pleased with themselves even when they mix everything up; but if you are a philosopher, I think you will do as I have said.”

“That is true,” said Simmias and Cebes together.

Excerpts from The Republic

Plato. Plato in Twelve Volumes, Vols. 5 & 6 translated by Paul Shorey. Cambridge, MA, Harvard University Press; London, William Heinemann Ltd. 1969.

The Analogy of the Divided Line (Book VI 509d-511e)

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Divided Line

“Conceive then,” said I, “as we were saying, that there are these two entities, and that one of them is sovereign over the intelligible order and region and the other over the world of the eye-ball, not to say the sky-ball, but let that pass. You surely apprehend the two types, the visible and the intelligible.”

“I do.”

“Represent them then, as it were, by a line divided into two unequal sections and cut each section again in the same ratio (the section, that is, of the visible and that of the intelligible order), and then as an expression of the ratio of their comparative clearness and obscurity you will have, as one of the sections of the visible world, images. By images I mean, first, shadows, and then reflections in water and on surfaces of dense, smooth and bright texture, and everything of that kind, if you apprehend.”

“I do.”

“As the second section assume that of which this is a likeness or an image, that is, the animals about us and all plants and the whole class of objects made by man.”

“I so assume it,” he said.

“Would you be willing to say,” said I, “that the division in respect of reality and truth or the opposite is expressed by the proportion: as is the opinable to the knowable so is the likeness to that of which it is a likeness?”

“I certainly would.”

“Consider then again the way in which we are to make the division of the intelligible section.”

“In what way?”

“By the distinction that there is one section of it which the soul is compelled to investigate by treating as images the things imitated in the former division, and by means of assumptions from which it proceeds not up to a first principle but down to a conclusion, while there is another section in which it advances from its assumption to a beginning or principle that transcends assumption, and in which it makes no use of the images employed by the other section, relying on ideas only and progressing systematically through ideas.”

“I don't fully understand what you mean by this,” he said.

“Well, I will try again,” said I,” for you will better understand after this preamble. For I think you are aware that students of geometry and reckoning and such subjects first postulate the odd and the even and the various figures and three kinds of angles and other things akin to these in each branch of science, regard them as known, and, treating them as absolute assumptions, do not deign to render any further account of them to themselves or others, taking it for granted that they are obvious to everybody. They take their start from these, and pursuing the inquiry from this point on consistently, conclude with that for the investigation of which they set out.”

“Certainly,” he said, “I know that.”

“And do you not also know that they further make use of the visible forms and talk about them, though they are not thinking of them but of those things of which they are a likeness, pursuing their inquiry for the sake of the square as such and the diagonal as such, and not for the sake of the image of it which they draw? And so in all cases. The very things which they mould and draw, which have shadows and images of themselves in water, these things they treat in their turn2 as only images, but what they really seek is to get sight of those realities which can be seen only by the mind.”

“True,” he said.

“This then is the class that I described as intelligible, it is true, but with the reservation first that the soul is compelled to employ assumptions in the investigation of it, not proceeding to a first principle because of its inability to extricate itself from and rise above its assumptions, and second, that it uses as images or likenesses the very objects that are themselves copied and adumbrated by the class below them, and that in comparison with these latter are esteemed as clear and held in honor.”

“I understand,” said he, “that you are speaking of what falls under geometry and the kindred arts.”

“Understand then,” said I, “that by the other section of the intelligible I mean that which the reason itself lays hold of by the power of dialectics, treating its assumptions not as absolute beginnings but literally as hypotheses, underpinnings, footings, and springboards so to speak, to enable it to rise to that which requires no assumption and is the starting-point of all, and after attaining to that again taking hold of the first dependencies from it, so to proceed downward to the conclusion, making no use whatever of any object of sense3 but only of pure ideas moving on through ideas to ideas and ending with ideas.4

“I understand,” he said; “not fully, for it is no slight task that you appear to have in mind, but I do understand that you mean to distinguish the aspect of reality and the intelligible, which is contemplated by the power of dialectic, as something truer and more exact than the object of the so-called arts and sciences whose assumptions are arbitrary starting-points. And though it is true that those who contemplate them are compelled to use their understanding and not their senses, yet because they do not go back to the beginning in the study of them but start from assumptions you do not think they possess true intelligence about them although the things themselves are intelligibles when apprehended in conjunction with a first principle. And I think you call the mental habit of geometers and their like mind or understanding and not reason because you regard understanding as something intermediate between opinion and reason.”

“Your interpretation is quite sufficient,” I said; “and now, answering to these four sections, assume these four affections occurring in the soul: intellection or reason for the highest, understanding for the second; assign belief to the third, and to the last picture-thinking or conjecture, and arrange them in a proportion, considering that they participate in clearness and precision in the same degree as their objects partake of truth and reality.”

“I understand,” he said; “I concur and arrange them as you bid.”

The Allegory of the Cave (Book VII 514a-520a)

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Allegory of the Cave

“Next,” said I, “compare our nature in respect of education and its lack to such an experience as this. Picture men dwelling in a sort of subterranean cavern5 with a long entrance open to the light on its entire width. Conceive them as having their legs and necks fettered from childhood, so that they remain in the same spot, able to look forward only, and prevented by the fetters from turning their heads. Picture further the light from a fire burning higher up and at a distance behind them, and between the fire and the prisoners and above them a road along which a low wall has been built, as the exhibitors of puppet-shows have partitions before the men themselves, above which they show the puppets.”

“All that I see,” he said.

“See also, then, men carrying6 past the wall implements of all kinds that rise above the wall, and human images and shapes of animals as well, wrought in stone and wood and every material, some of these bearers presumably speaking and others silent.”

“A strange image you speak of,” he said, “and strange prisoners.”

“Like to us,” I said; “for, to begin with, tell me do you think that these men would have seen anything of themselves or of one another except the shadows cast from the fire on the wall of the cave that fronted them?”

“How could they,” he said, “if they were compelled to hold their heads unmoved through life?”

“And again, would not the same be true of the objects carried past them?”


“If then they were able to talk to one another, do you not think that they would suppose that in naming the things that they saw7 they were naming the passing objects?”


“And if their prison had an echo8 from the wall opposite them, when one of the passersby uttered a sound, do you think that they would suppose anything else than the passing shadow to be the speaker?”

“By Zeus, I do not,” said he.

“Then in every way such prisoners would deem reality to be nothing else than the shadows of the artificial objects.”

“Quite inevitably,” he said.

“Consider, then, what would be the manner of the release and healing from these bonds and this folly if in the course of nature something of this sort should happen to them: When one was freed from his fetters and compelled to stand up suddenly and turn his head around and walk and to lift up his eyes to the light, and in doing all this felt pain and, because of the dazzle and glitter of the light, was unable to discern the objects whose shadows he formerly saw, what do you suppose would be his answer if someone told him that what he had seen before was all a cheat and an illusion, but that now, being nearer to reality and turned toward more real things, he saw more truly? And if also one should point out to him each of the passing objects and constrain him by questions to say what it is, do you not think that he would be at a loss and that he would regard what he formerly saw as more real than the things now pointed out to him?”

“Far more real,” he said.

“And if he were compelled to look at the light itself, would not that pain his eyes, and would he not turn away and flee to those things which he is able to discern and regard them as in very deed more clear and exact than the objects pointed out?”

“It is so,” he said.

“And if,” said I, “someone should drag him thence by force up the ascent which is rough and steep, and not let him go before he had drawn him out into the light of the sun, do you not think that he would find it painful to be so haled along, and would chafe at it, and when he came out into the light, that his eyes would be filled with its beams so that he would not be able to see even one of the things that we call real?”

“Why, no, not immediately,” he said.

“Then there would be need of habituation, I take it, to enable him to see the things higher up. And at first he would most easily discern the shadows and, after that, the likenesses or reflections in water of men and other things, and later, the things themselves, and from these he would go on to contemplate the appearances in the heavens and heaven itself, more easily by night, looking at the light of the stars and the moon, than by day the sun and the sun's light.9

“Of course.”

“And so, finally, I suppose, he would be able to look upon the sun itself and see its true nature, not by reflections in water or phantasms of it in an alien setting,10 but in and by itself in its own place.”

“Necessarily,” he said.

“And at this point he would infer and conclude that this it is that provides the seasons and the courses of the year and presides over all things in the visible region, and is in some sort the cause of all these things that they had seen.”

“Obviously,” he said, “that would be the next step.”

“Well then, if he recalled to mind his first habitation and what passed for wisdom there, and his fellow-bondsmen, do you not think that he would count himself happy in the change and pity them?”

“He would indeed.”

“And if there had been honors and commendations among them which they bestowed on one another and prizes for the man who is quickest to make out the shadows as they pass and best able to remember their customary precedences, sequences and coexistences,11 and so most successful in guessing at what was to come, do you think he would be very keen about such rewards, and that he would envy and emulate those who were honored by these prisoners and lorded it among them, or that he would feel with Homer and ‘greatly prefer while living on earth to be serf of another, a landless man,’ and endure anything rather than opine with them and live that life?”

“Yes,” he said, “I think that he would choose to endure anything rather than such a life.”

“And consider this also,” said I, “if such a one should go down again and take his old place would he not get his eyes full of darkness, thus suddenly coming out of the sunlight?”

“He would indeed.”

“Now if he should be required to contend with these perpetual prisoners in 'evaluating' these shadows while his vision was still dim and before his eyes were accustomed to the dark—and this time required for habituation would not be very short—would he not provoke laughter, and would it not be said of him that he had returned from his journey aloft with his eyes ruined and that it was not worth while even to attempt the ascent? And if it were possible to lay hands on and to kill the man who tried to release them and lead them up, would they not kill him?”12

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Daniel Nicholas Chodowiecki: ''The Death of Socrates'' 18th - 19th century

“They certainly would,” he said.

“This image then, dear Glaucon, we must apply as a whole to all that has been said, likening the region revealed through sight to the habitation of the prison, and the light of the fire in it to the power of the sun. And if you assume that the ascent and the contemplation of the things above is the soul's ascension to the intelligible region, you will not miss my surmise, since that is what you desire to hear. But God knows whether it is true. But, at any rate, my dream as it appears to me is that in the region of the known the last thing to be seen and hardly seen is the idea of good, and that when seen it must needs point us to the conclusion that this is indeed the cause for all things of all that is right and beautiful, giving birth in the visible world to light, and the author of light and itself in the intelligible world being the authentic source of truth and reason, and that anyone who is to act wisely in private or public must have caught sight of this.”

“I concur,” he said, “so far as I am able.”

“Come then,” I said, “and join me in this further thought, and do not be surprised that those who have attained to this height are not willing to occupy themselves with the affairs of men, but their souls ever feel the upward urge and the yearning for that sojourn above. For this, I take it, is likely if in this point too the likeness of our image holds.”

“Yes, it is likely.”

“And again, do you think it at all strange,” said I, “if a man returning from divine contemplations to the petty miseries of men cuts a sorry figure and appears most ridiculous, if, while still blinking through the gloom, and before he has become sufficiently accustomed to the environing darkness, he is compelled in courtrooms or elsewhere to contend about the shadows of justice or the images that cast the shadows and to wrangle in debate about the notions of these things in the minds of those who have never seen justice itself?”

“It would be by no men strange,” he said.

“But a sensible man,” I said, “would remember that there are two distinct disturbances of the eyes arising from two causes, according as the shift is from light to darkness or from darkness to light, and, believing that the same thing happens to the soul too, whenever he saw a soul perturbed and unable to discern something, he would not laugh unthinkingly, but would observe whether coming from a brighter life its vision was obscured by the unfamiliar darkness, or whether the passage from the deeper dark of ignorance into a more luminous world and the greater brightness had dazzled its vision.13 And so14 he would deem the one happy in its experience and way of life and pity the other, and if it pleased him to laugh at it, his laughter would be less laughable than that at the expense of the soul that had come down from the light above.”

“That is a very fair statement,” he said.

“Then, if this is true, our view of these matters must be this, that education is not in reality what some people proclaim it to be in their professions. What they aver is that they can put true knowledge into a soul that does not possess it, as if they were inserting vision into blind eyes.”

“They do indeed,” he said.

“But our present argument indicates,” said I, “that the true analogy for this indwelling power in the soul and the instrument whereby each of us apprehends is that of an eye that could not be converted to the light from the darkness except by turning the whole body. Even so this organ of knowledge must be turned around from the world of becoming together with the entire soul, like the scene-shifting periact15 in the theater, until the soul is able to endure the contemplation of essence and the brightest region of being. And this, we say, is the good,16 do we not?”


“Of this very thing, then,” I said, “there might be an art,17 an art of the speediest and most effective shifting or conversion of the soul, not an art of producing vision in it, but on the assumption that it possesses vision but does not rightly direct it and does not look where it should, an art of bringing this about.”

“Yes, that seems likely,” he said.

“Then the other so-called virtues18 of the soul do seem akin to those of the body. For it is true that where they do not pre-exist, they are afterwards created by habit and practice. But the excellence of thought, it seems, is certainly of a more divine quality, a thing that never loses its potency, but, according to the direction of its conversion, becomes useful and beneficent, or, again, useless and harmful. Have you never observed in those who are popularly spoken of as bad, but smart men, how keen is the vision of the little soul, how quick it is to discern the things that interest it,19 a proof that it is not a poor vision which it has, but one forcibly enlisted in the service of evil, so that the sharper its sight the more mischief it accomplishes?”

“I certainly have,” he said.

“Observe then,” said I, “that this part of such a soul, if it had been hammered from childhood, and had thus been struck free of the leaden weights, so to speak, of our birth and similar pleasures and gluttonies turn downwards the vision of the soul—if, I say, freed from these, it had suffered a conversion towards the things that are real and true, that same faculty of the same men would have been most keen in its vision of the higher things, just as it is for the things toward which it is now turned.”

“It is likely,” he said.

“Well, then,” said I, “is not this also likely and a necessary consequence of what has been said, that neither could men who are uneducated and inexperienced in truth ever adequately preside over a state, nor could those who had been permitted to linger on to the end in the pursuit of culture—the one because they have no single aim and purpose in life to which all their actions, public and private, must be directed, and the others, because they will not voluntarily engage in action, believing that while still living they have been transported to the Islands of the Blest.”

“True,” he said.

“It is the duty of us, the founders, then,” said I, “to compel the best natures to attain the knowledge which we pronounced the greatest, and to win to the vision of the good, to scale that ascent, and when they have reached the heights and taken an adequate view, we must not allow what is now permitted.”

“What is that?”

“That they should linger there,” I said, “and refuse to go down again among those bondsmen and share their labors and honors, whether they are of less or of greater worth.”

“Do you mean to say that we must do them this wrong, and compel them to live an inferior life when the better is in their power?”

“You have again forgotten, my friend,” said I, “that the law is not concerned with the special happiness of any class in the state, but is trying to produce this condition20 in the city as a whole, harmonizing and adapting the citizens to one another by persuasion and compulsion, and requiring them to impart to one another any benefit which they are severally able to bestow upon the community, and that it itself creates such men in the state, not that it may allow each to take what course pleases him, but with a view to using them for the binding together of the commonwealth.”

“True,” he said, “I did forget it.”

“Observe, then, Glaucon,” said I, “that we shall not be wronging, either, the philosophers who arise among us, but that we can justify our action when we constrain them to take charge of the other citizens and be their guardians.”21

Further Reading

Brickhouse, Thomas, and Nicholas D. Smith. "Plato." The Internet Encyclopedia of Philosophy.

"Dialogues of Plato." Internet Sacred Text Archive.

Kraut, Richard. "Plato." The Stanford Encyclopedia of Philosophy (Fall 2013 Edition). Ed. Edward N. Zalta.

Losin, Peter. "Plato and Platonism." 2000.

Perseus Digital Library.

Rehmeyer, Julie. "Still Debating with Plato." Science News. 25 Apr. 2008.

WorldCat Identities Network. Plato.


  1. Image CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons. ^
  2. i.e. a bronze sphere would be the original of its imitative reflection in water, but it is in turn only the imperfect imitation of the mathematical idea of a sphere. ^
  3. This is one of the passages that are misused to attribute to Plato disdain for experience and the perceptions of the senses . . . The dialectician is able to reason purely in concepts and words without recurring to images. Plato is not here considering how much or little of his knowledge is ultimately derived from experience. ^
  4. The description undoubtedly applies to a metaphysical philosophy that deduces all things from a transcendent first principle. I have never denied that. The point of my interpretation is that it also describes the method which distinguishes the dialectician as such from the man of science, and that this distinction is for practical and educational purposes the chief result of the discussion, as Plato virtually says in the next few lines. ^
  5. The image of the cave illustrates by another proportion the contrast between the world of sense-perception and the world of thought. Instead of going above the plane of ordinary experience for the other two members of the proportion, Plato here goes below and invents a fire and shadows cast from it on the walls of a cave to correspond to the sun and the “real” objects of sense. In such a proportion our “real” world becomes the symbol of Plato's ideal world. Modern fancy may read what meanings it pleases into the Platonic antithesis of the “real” and the “ideal.” It has even been treated as an anticipation of the fourth dimension. But Plato never leaves an attentive and critical reader in doubt as to his own intended meaning. There may be at the most a little uncertainty as to which are merely indispensable parts of the picture. ^
  6. The men are merely a part of the necessary machinery of the image. Their shadows are not cast on the wall. The artificial objects correspond to the things of sense and opinion in the divided line, and the shadows to the world of reflections. ^
  7. As we use the word tree of the trees we see, though the reality is the idea of a tree, so they would speak of the shadows as the world, though the real reference unknown to them would be to the objects that cause the shadows, and back of the objects to the things of the “real” world of which they are copies. The general meaning, which is quite certain, is that they would suppose the shadows to be the realities. ^
  8. The echo and the voices merely complete the picture. ^
  9. It is probably a mistake to look for a definite symbolism in all the details of this description. There are more stages of progress than the proportion of four things calls for. All that Plato's thought requires is the general contrast between an unreal and a real world, and the goal of the rise from one to the other in the contemplation of the sun, or the idea of good. ^
  10. I.e., a foreign medium. ^
  11. Another of Plato's anticipations of modern thought. This is precisely the Humian, Comtian, positivist, pragmatist view of causation. ^
  12. An allusion to the death of Socrates, who was executed for purportedly corrupting the youth of Athens with his teaching. ^
  13. Lit. “or whether coming from a deeper ignorance into a more luminous world, it is dazzled by the brilliance of a greater light.” ^
  14. I.e., only after that. ^
  15. Probably a reference to the triangular prisms on each side of the stage. They revolved on an axis and had different scenes painted on their three faces. Many scholars are of the opinion that they were not known in the classical period, as they are mentioned only by late writers; but others do not consider this conclusive evidence, as a number of classical plays seem to have required something of the sort. ^
  16. Hard-headed distaste for the unction or seeming mysticism of Plato's language should not blind us to the plain meaning. Unlike Schopenhauer, who affirms the moral will to be unchangeable, Plato says that men may be preached and drilled into ordinary morality, but that the degree of their intelligence is an unalterable endowment of nature. Some teachers will concur. ^
  17. Plato often distinguishes the things that do or do not admit of reduction to an art or science. ^
  18. This then is Plato's answer (intended from the first) to the question whether virtue can be taught, debated in the Protagoras and Meno. The intellectual virtues (to use Aristotle's term), broadly speaking, cannot be taught; they are a gift. And the highest moral virtue is inseparable from rightly directed intellectual virtue. Ordinary moral virtue is not rightly taught in democratic Athens, but comes by the grace of God. In a reformed state it could be systematically inculcated and “taught.” ^
  19. Lit. “Toward which it is turned.”and becoming, which attaching themselves to it by food ^
  20. I.e., happiness, not of course exceptional happiness. ^
  21. Noblesse oblige, or the obligation of the better off (e.g., in social status, wealth, or education) to help and take responsibility for those who are disadvantaged (e.g., of lower social status, poor or less educated). ^

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