[1]: 169 Instead he draws an analogy and offers to talk about "the child of goodness"[1]: 169 (Ancient Greek: "ἔκγονός τε τοῦ ἀγαθοῦ").
While the analogy sets forth both epistemological and ontological theories, it is debated whether these are most authentic to the teaching of Socrates or its later interpretations by Plato.
David Hume once wrote, "All our reasonings concerning matters of fact are founded on a species of Analogy.
— The Republic VI (508c)[1]: 171 In other words, Plato is saying that the true nature of reality cannot be comprehended by the ordinary senses.
— The Republic VI (508d)[1]: 171 Having made these claims, Socrates asks Glaucon, "...which of the gods in heaven can you put down as cause and master of this, whose light makes our sight see so beautifully and the things to be seen?"
Socrates argues that the bodily senses can only bring us to opinions, conveying an underlying assumption that true knowledge is of that which is not subject to change.
Instead, Socrates continues, knowledge is to be found in "... that region in which truth and real being brightly shine..." (508d) This is the intelligible illuminated by the highest idea, that of goodness.
Through this analogy, Socrates helped Glaucon come to the realization that Goodness is of inestimable value, being both the source of knowledge and truth, as well as more valuable and unattainable than both.
Even today, humans still use all kinds of mathematical models, the physics of electromagnetic measurements, deductions, and logic to further know and understand the real sun as a fascinating being.
— The Republic VI (509b)[3] Socrates' main concern was that he did not want his followers to place Goodness, Knowledge, and Truth all on the same level.
[5] Incidentally, the metaphor of the Sun exemplifies a traditional interrelation between metaphysics and epistemology: interpretations of fundamental existence create—and are created by—ways of knowing.
Socrates, using the Simile of the Sun as a foundation, continues with the Analogy of the Divided Line (509d–513e) after which follows the Allegory of the Cave (514a–520a).
The divided line gives the details of the four stage process of moving from opinions, or shadows, all the way up to mathematics, logic, deduction, and the dialectical method.