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A Psychiatrist and Philosopher Explains the Three Great Metaphors at the Heart of Plato’s Republic

By Dr Neel Burton — Psychiatrist, philosopher, and wine writer; Fellow of Green Templeton College, University of Oxford; author of over twenty books.

Plato’s Sun, Line, and Cave are not three separate allegories, but one extraordinary vision of reality, knowledge, and truth.

Plato’s Republic culminates in three of the most influential metaphors in the history of philosophy: the Sun, the Divided Line, and the Cave. Together they explain the nature of reality, the possibility of knowledge, the purpose of education, and why philosophers should rule.

When Plato first appeals to the Forms (or Theory of Forms) at the end of Book V of the Republic, he assumes that the reader is already familiar with the concept, perhaps from earlier dialogues such as the Phaedo and Phaedrus. But now, in discussing the education of the guardians, he introduces the elusive Form of the Good [hē toû agathoû idea]. It is by attaining the Form of the Good that the philosopher-king is made fit to rule.

Because the Form of the Good is impossible to describe and difficult even to imagine, Socrates conveys its essence through three connected metaphors: the Sun, the Line, and the Cave.

The three metaphors are not independent. The Sun explains what the Good is. The Line explains the levels of knowledge. The Cave shows the soul’s journey through those levels.

The Metaphor of the Sun

Just as it is by the light of the sun that the visible is made apparent to the eye, so it is by the light of truth and being – in contrast to the twilight of becoming and perishing – that the nature of reality is made apprehensible to the soul.
Just as light and sight may be said to be like the sun, and yet not to be the sun, so science and truth may be said to be like the Good, and yet not to be the Good; it is by the sun that there is light and sight, and it is by the Good that there is science and truth.
Just as the sun is the author of nourishment and generation, so the Good is the author of being and essence. Thus, the Good is beyond being, and the cause of all existence. The Sun is therefore not merely a metaphor for goodness, but for the very possibility of knowledge itself.

The Metaphor of the Line

A line is cut into two unequal parts, and each of them is divided again in the same proportion. The two main divisions correspond to the intelligible world and to the visible world. One section in the visible division consists of images, that is,
shadows and reflections, and is accessed through imagination. The other, higher section in the visible division consists of sensible particulars and is accessed through belief. One section in the intelligible division consists of Forms and is accessed through thought, but via sensible particulars and hypotheses, as when geometers use a picture of a triangle to help reason about triangularity, or make appeal to axioms to prove theorems. The other, higher section in the intelligible division also consists of Forms but is accessed by understanding, a purely abstract science which requires neither sensible particulars nor hypotheses, but only an unhypothetical first principle, namely, the Form of the Good. The purpose of education is to move the philosopher through the various sections of the line until he reaches the Form of the Good.

The Metaphor or Allegory of the Cave

Human beings have spent all their lives in an underground cave or den which has a mouth open towards the light. They have their legs and their necks chained so that they cannot move, and can see only in front of them, towards the back of the cave. Above and behind them a fire is blazing, and between them and the fire there is a raised way along which there is a low wall. Men pass along the wall carrying all sorts of statues, and the fire throws the shadows of these statues onto the back of the cave. All the prisoners ever see are the shadows, and so they suppose that the shadows are the objects themselves.

If a prisoner is unshackled and turned towards the light, he suffers sharp pains, but in time he begins to see the statues and moves from the cognitive stage of imagination to that of belief. The prisoner is then dragged out of the cave, where the light is so bright that he can only look at the shadows, and then at the reflections, and then finally at the objects themselves: not statues this time, but real objects. In time, he looks up at the sun, and understands that the sun is the cause of everything that he sees around him, of light, of vision, and of the objects of vision. In so doing, he passes from the cognitive stage of thought to that of understanding.

The purpose of education is to drag the prisoner as far out of the cave as possible; not to instil knowledge into his soul, but to turn his whole soul towards the sun, which is the Form of the Good. Once out of the cave, the prisoner is reluctant to descend back into the cave and get involved in human affairs. When he does, his eyes are no longer accustomed to the darkness, and he appears ridiculous to his fellow prisoners. However, he must be made to descend back into the cave and partake of human labours and honours, whether they are worth having or not. This is because the State aims not at the happiness of a single person or single class, but at the happiness of all its citizens. In any case, the prisoner has a duty to give service to the State, since it is by the State that he was educated to see the light of the sun.

The State in which the rulers are most reluctant to govern is always the best and most quietly governed, and the State in which they are most eager, the worst… You must contrive for your future rulers another and a better life than that of a ruler, and then you may have a well-ordered State; for only in the State which offers this, will they rule who are truly rich, not in silver and gold, but in virtue and wisdom, which are the true blessings of life… And the only life which looks down upon the life of political ambition is that of true philosophy. Do you know of any other?

Taken together, the Sun, the Line, and the Cave are not three separate metaphors but one of the most ambitious philosophical visions ever conceived. They explain not only what reality is, but how we come to know it, why education transforms us, and why wisdom carries with it a responsibility to serve others.