Writing in the great work Republic, Plato said that the problem of states will not go away until philosophers become kings, that is, knowledge of ideas is necessary. Plato's ideas were influenced by Athens and Sparta. Plato said that the soul is real and the body is physical, that is, the pleasure of the body is momentary, the reality is in the soul. Plato said in the Republic that a person should act on the basis of knowledge such as a person satisfied with lust should produce, a courageous person should be a soldier and a prudent person should be a ruler. Plato said that the world of ideas is knowledge, that is, the real world, while the material world is influenced by opinion, that is, imaginary. Commenting on Plato's views, Karl Popper said that Plato is the enemy of free society. Because he leaves the individual at the will of the king and ignores the rights and liberties of the individual. Plato talked about the unity of the state because Plato's thoughts were influen...