The divided line (509d–511e)

A line cut in two and each part cut again in the same ratio: images, then visible things, then mathematical reasoning that argues from assumptions, then the intelligible reached without assumptions. Four states of mind — eikasia, pistis, dianoia, noēsis — and each is a way of being related to what is real.

The measuring device for the whole story: the walk-in tracks your place on it as you climb. It is also the closest thing in Greek to a four-worlds scheme — and the Tree's Assiah, Yetzirah, Beriah and Atzilut are a genuinely startling parallel, arrived at from other soil.