Justice in a person and a city › The Allegory of the Sun and the Divided Line

To explain what philosophers know that others do not, Plato introduces two more images. The sun, he says, is to the visible world what the Form of the Good is to the intelligible world. Just as the sun provides the light by which we see and helps living things grow, the Good provides both the intelligibility by which we understand and the being by which things exist. Socrates says the Good gives knowable things their truth and being, while itself being beyond being in dignity and power (Book VI, 508e–509b). Exactly how to interpret that claim is a further philosophical question. The Divided Line illustrates the levels of cognition. The lowest section is imagination (_eikasia_), concerned with images such as shadows and reflections. Above that is belief (_pistis_), directed toward the visible things those images represent. Higher still is mathematical reasoning (_dianoia_): working with abstract concepts but still relying on assumptions. At the top is dialectical knowledge (_noesis_): grasping the Forms themselves and the Good that grounds them all. ::: {.callout-tip title="Practical Application"} The Divided Line invites a useful question about your own reasoning: which assumptions are you treating as starting points? This is a modern exercise inspired by the image. It does not make every unexamined opinion Plato's technical *pistis*, or every argument from assumptions mathematics. :::