The Divided Line and the Degrees of Cognition

In Book VI of the Republic, Plato asks us to imagine a line divided into four unequal segments, each standing for a different way of knowing and a different grade of reality. At the bottom sits eikasia, the mind's traffic in mere images and shadows; above it pistis, the confident belief we have about ordinary visible things. Higher still is dianoia, the reasoning of the mathematician who argues from assumed premises and visible diagrams; and at the summit noesis, the pure intellection that grasps the Forms themselves, ascending without props to the Form of the Good. The same ascent is dramatized in the allegory of the Cave: education is the soul's climb up these rungs, from illusion toward what is most truly real.