Plato's theory of ideal state included compulsory education managed by the state, divided into elementary and higher education with three phases. The first phase focused on gymnastics, music, and mathematics from ages 0-18, followed by military training from 18-20. The second phase from ages 21-35 continued dialectics, geography, astronomy and other subjects. The third phase from ages 35-50 involved further advanced studies abroad. Plato also proposed a theory of communism with functional specialization, non-interference, and social harmony. His theory of justice aimed to differentiate the importance of harmony and non-interference.