In Book IV the happiness of the guardians, so strenuously trained, is questioned.
Socrates takes the objections of his auditors in due stride, reminding them of their original premise: that the State is to be for the good of the many and not the few. Their State has grown larger in the meantime, and is beginning to divide its labors. Defense and security against neighbors and foreign invasion enter the debate.
But surely, Socrates says, the education, military and otherwise, that the citizens have garnered, coupled with their love for the State and their solidarity, will repel or outwit all challenges. Believing that what they have created thus far is a perfect State, the philosopher once again seek out justice.
Socrates suggests they proceed by a process of elimination among the four virtues. He defines courage, temperance, and wisdom, but must digress before attaining justice.
The digression yields the three principles of the soul: reason, passion, and appetite. When these exist in harmony, Socrates concludes, there is justice. It is a provisional definition.
