Step 1: Understanding the Concept:
The question traces the historical and philosophical origin of natural law, which is the foundation for the principles of natural justice. Natural law theory posits that there are universal moral and ethical principles inherent in human nature and that these principles form the basis for a just legal system.
Step 2: Detailed Explanation:
- The Stoics, ancient Greek and Roman philosophers (like Cicero), are credited with developing the concept of natural law. They believed in 'logos' – a universal reason or divine law that governs the cosmos. They argued that human law should align with this higher, rational natural law to be considered just. This idea of a universal, inherent justice is the direct ancestor of modern concepts of natural justice.
- Positivists (like Austin and Hart) and the Analytical School are essentially the same. They argue that law is what is 'posited' or laid down by the sovereign or a recognized authority. They separate law from morality and would not attribute the development of natural justice to a higher moral law.
- The Historical School (like Savigny) believed that law is not made but is found in the customs, traditions, and spirit of the people (\textit{Volksgeist}). Their focus was on the organic growth of law from society, not on universal rational principles.
Step 3: Final Answer:
The development and popularization of the idea of natural law, from which natural justice principles are derived, is historically attributed to the Stoics.