It has to be kept in mind that ideal state of Plato is not a historical one. It has
not become concretein any period of history. It is timeless. Four elements affect the degeneration of the states: disappearance of internal harmony of society, violation of division of labour within the society, emergence of economical class conflicts, and finally, moral corruption and destruction of unity of the rulers.

"A) The need of mass for social knowledge" is one of the reasons
for the birth of sophist thought in Athens.