3. The greatest of all evils is realized with this: truly poor people are not part of the society, as they are not part of any of its parts (soldiers, craftsmen, etc.); they have no stake in or involvement in the city.
4. The state is powerless in war--either the weak oligarchs are forced to fight, and they will always be defeated because they are unfit and few, or they are forced to arm the poor, who may well rebel.
When the poor people finally do rebel, kick out the wealthy, and re-distribute the land and goods, democracy arises. Democracy is characterized by a total freedom of anyone to do anything, which at first may seem ideal, but in fact lapses into total anarchy, chaos, hedonism, and lack of personal or societal discipline. Socrates says that democracy eventually lapses back into a semi- oligarchy, where a few members take advantage of the freedom presented to amass great wealth and power, and the people, justly or not, seek to depose them.
To depose these purported oligarchs, the people choose a champion. The many, being more powerful than the few, are able to put their champion in control, and he is at first very promising, but soon he starts amassing power and destroying anyone who threatens his own power, which eventually means killing anyone wise, brave, or strong. He thus cripples the state and amasses power for himself until the state becomes a full-blown tyranny.
Commentary .
The first interesting thing one might point out in this section is that Plato appears to believe that the dissolution of his Just City is inevitable. Despite all the safeguards he's put in place, Plato seems confident that his system of eugenics and breeding for the best will eventually fail. There are no signs anywhere else in the Republic of this sort of pessimism about the state. If one looks to Plato's broader philosophy, however, the reason for this is evident. His Just City adheres to the Form of the just, however, it itself is not that Form, and therefore it is not unchanging, ungrowing, etc.
