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: " "). 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."
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