[109] The knowledge that comes from the sciences usually is expressed in propositions and is laid before us in the form of conclusions that we can grasp and put to use. But the “doctrine” of a thinker is that which, within what is said, remains unsaid, that to which we are exposed so that we might expend ourselves on it.

In order to experience and to know for the future what a thinker left unsaid, whatever that might be, we have to consider what he said. To properly satisfy this demand would entail examining all of Plato's “dialogues” in their interrelationship. Since this is impossible, we must let a different path guide us to the unsaid in Plato's thinking.

What remains unsaid in Plato's thinking is a change in what determines the essence of truth. The fact that this change does take place, what it consists in, and what gets grounded through this transformation of the essence of truth – all of that can be clarified by an interpretation of the “allegory of the cave.”

The “allegory of the cave” is presented at the beginning of the seventh book of the “dialogue” on the essence of the πόλιζ (Republic, VII, 514 a2 to 517 a7). The “allegory” tells a story. The tale unfolds in the conversation between Socrates and Glaucon. Socrates presents the story, Glaucon shows his awakening astonishment.