The greatest of Socrates' disciples was Plato (427-347 BC). This philosopher believed that the soul had known the meanings of things in the period before it came on Earth. Thus all knowledge in the terrestrial world is essentially a memory of what the soul had seen before it entered the body and then forgot. So, when the soul sees in the earthly world things that resemble its formerly superhuman forms, it awakens and feels nostalgia for the eternal archetype. This state evokes true love or otherwise "Platonic love", that is, the soul's desire to know the real beings and to imitate them in the earthly world.
The conquest of knowledge, according to Plato, takes place through dialogue. Through this, the meanings and the relations between them are determined. Meanings contribute to the approach of eternal and pre-existing ideas, which are, according to the philosopher, the real beings and the cause of everything that happens in the world. In fact, the idea of the good was considered by Plato as the ultimate purpose of the world.
For the soul, the philosopher formulated the following theory: The soul once inhabited the world of ideas but the laws of the earthly world forced it to enter the body and come to the earthly world. Depending on its actions on earth, the soul after the death of the body is either released immediately and returns to the divine world or enters successively into bodies of other living organisms, until it is completely cleansed of its faults and can one day return to the divine world.
According to Plato, the soul is not an idea but a relative of it. Also, the way for the soul to know the divine, the ideal is to become the same as it. In order for the soul to know the beautiful and the good, it must become beautiful and good itself. Finally, in order to know God, the soul must know the idea of the good, which, as foretold, is the ultimate purpose of the world.
Plato believed, like his teacher, Socrates, that no one is bad at will but only because he does not know good. This implies that the knowledge of good leads to virtue, so virtue is instructive.
In a political level, Plato believed that the purpose of the state is the spiritual and moral promotion of its citizens, so the good politician must move towards their achievement. In the ideal city, according to the philosopher, there are three categories of citizens: Professionals, security guards and lords. The professionals form the largest team of citizens and with their work they maintain the rest. The guards protect the state in case of external and internal dangers. Finally, the lords come from the guard class, after careful selection, and aim to rule.
According to the philosopher, the guards must acquire music and gymnastics education. The first contributes to knowledge and the second to will. However, in order not to use their skills only for their own benefit and not for the common good, Plato considered that the guards should not have property but instead are required to stay in camps and be feeded there.
Finally, as far as the lords are concerned, they should have at the highest level the virtues of the guards and always act guided by the happiness of all the whole group of citizens.
