From a "comic strip" papyrus dating from Egypt's New Kingdom to the works of Stein, Joyce, and Barth, "nonsense" texts reveal a set of possibilities as rich and complex as the more conventional system of "making sense" from which they are derived.

Of he many excellences which I perceive in the order of our State, there is none which upon reflection pleases me better than the rule about poetry. To what do you refer? To the rejection of imitative poetry, which certainly ought not to be received; as I see far more clearly now that the parts of the soul have been distinguished. What do you mean? Speaking in confidence, for I should not like to have my words repeated to the tragedians and the rest of the imitative tribe --but I do not mind saying to you, that all poetical imitations are ruinous to the understanding of the hearers, and that the knowledge of their true nature is the only antidote to them. Explain the purport of your remark. Well, I will tell you, although I have always from my earliest youth had an awe and love of Homer, which even now makes the words falter on my lips, for he is the great captain and teacher of the whole of that charming tragic company; but a man is not to be reverenced more than the truth, and therefore I will speak out.

Socrates has now completed the main argument of The Republic; he has defined justice and shown it to be worthwhile. He turns back to the postponed question concerning poetry about human beings. In a surprising move, he banishes poets from the city. He has three reasons for regarding the poets as unwholesome and dangerous. First, they pretend to know all sorts of things, but they really know nothing at all. It is widely considered that they have knowledge of all that they write about, but, in fact, they do not. The things they deal with cannot be known: they are images, far removed from what is most real. By presenting scenes so far removed from the truth poets, pervert souls, turning them away from the most real toward the least.

Plato realizes that the general run of humankind can think, and speak, etc., without (so far as they acknowledge) any awareness of his realm of Forms.

The allegory of the cave is supposed to explain this.

In the allegory, Plato likens people untutored in the Theory of Forms to prisoners chained in a cave, unable to turn their heads. All they can see is the wall of the cave. Behind them burns a fire.  Between the fire and the prisoners there is a parapet, along which puppeteers can walk. The puppeteers, who are behind the prisoners, hold up puppets that cast shadows on the wall of the cave. The prisoners are unable to see these puppets, the real objects, that pass behind them. What the prisoners see and hear are shadows and echoes cast by objects that they do not see.