Natural law was initially defined by ancient Greek philosophers such as Aristotle and Plato. Plato did not have a theory on natural law; however, some of his theories involved concepts of natural law. On the other hand, Aristotle focused on the distinction between law and nature. It then led to the introduction of natural justice, which can be attributed to the Stoics.
In Plato’s Republic, justice is discussed in relation to the individual and the state. Plato argues that justice is a virtue that is necessary for both individual happiness and social harmony. He defines justice as each part of the soul performing its proper function and each class in society performing its proper role.
Aristotle, in his Nicomachean Ethics, discusses justice in terms of what is lawful and what is fair. He argues that justice is a mean between doing harm and suffering harm and that it involves giving people what they are due. Aristotle also discusses statesmanship in his Politics, where he argues that the best form of government is one that promotes the common good and allows citizens to live a good life.