The philosophers continue the debate in Book II by introducing a new definition that belongs more to political philosophy than pure philosophy: that justice is a legally enforced compromise devised for the mutual protection of citizens of a state.
In other words, justice is a fabrication of the State that prevents citizens from harming one another. Socrates is certainly up to the challenge. He dislikes the idea that justice does not exists naturally, but that it must be externally and superficially imposed to discourage unjust behavior.
Adeimantus' mentioning of the State seems fortuitous, but it is as if Socrates has been waiting for it all along. Uncertain whether they can arrive at an acceptable definition of justice any other way, Socrates proposes they construct a State of which they approve, and see if they might not find justice lurking in it somewhere.
This State arises, Socrates says, "out of the needs of mankind." And the immense project of building a State from its very foundation has officially commenced. Basic necessities are addressed first, then the primitive division of labor, followed by the rudiments of education.
Within the ideal State, Socrates maintains, there will be no need for "bad fictions," or manipulative poetics in general, since education must be perfectly moral.
