Analogy of the sun

The analogy of the sun (or simile of the sun or metaphor of the sun) is found in the sixth book of The Republic (507b–509c), written by the Greek philosopher Plato as a dialogue between Glaucon (Plato's elder brother) and Socrates (narrated by the latter). Upon being urged by Glaucon to define goodness, a cautious Socrates professes himself incapable of doing so. Instead he draws an analogy and offers to talk about "the child of goodness" (Greek: "ἔκγονός τε τοῦ ἀγαθοῦ"). Socrates reveals this "child of goodness" to be the sun, proposing that just as the sun illuminates, bestowing the ability to see and be seen by the eye, with its light so the idea of goodness illumines the intelligible with truth. 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. The sun is a metaphor for the nature of reality and knowledge concerning it.

Plato's use of such an analogy can be interpreted for many different reasons in philosophy. For example, Plato uses them to illustrate and help illuminate his arguments. In the Analogy of the Sun, Socrates compares the "Good" with the sun. Plato might be using the image of the sun to help bring life to his arguments or to make the argument more clearly understood. David Hume once wrote, "All our reasonings concerning matters of fact are founded on a species of Analogy."

Plato makes the claim that "sight and the visible realm are deficient." He argues that for the other senses to be used all that is needed is the sense itself and that which can be sensed by it (e.g., to taste sweetness, one needs the sense of taste and that which can be tasted as sweet), but "even if a person's eyes are capable of sight, and he's trying to use it, and what he's trying to look at is coloured, the sight will see nothing and the colours will remain unseen, surely, unless there is also present an extra third thing which is made specifically for this purpose." The third thing Plato is talking about is light. Through this analogy he equates that which gives us natural light, the sun, as the source of goodness in this world.

In other words, Plato is saying that the true nature of reality cannot be comprehended by the ordinary senses. Thus, we should make use of the mind rather than the sensory organs to better understand the higher truths of the universe. The mind, much like sight, requires a "third thing" to function properly, and that third thing is Plato's idea of goodness. He likens a mind without goodness to sight without light; one cannot operate at peak efficiency without the other.

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