Virtue is innate and cannot be learned, no one does bad on purpose, and to know what is good results in doing what is good;
Knowledge is virtue.
In the Republic, Plato poses the question, "What is justice?" and by examining both individual justice and the justice that informs societies, Plato is able not only to inform metaphysics, but also ethics and politics with the question:
"What is the basis of moral and social obligation?"
Plato's well-known answer rests upon the fundamental responsibility to seek wisdom, wisdom which leads to an understanding of the Form of the Good.
Plato views "The Good" as the supreme Form, somehow existing even "beyond being".
In this manner, justice is obtained when knowledge of how to fulfill one's moral and political function in society is put into practice.