Natural law requires a minimal moral content as a prerequisite for viewing something as in contravention of the law, while the positivist school holds that the law is whatever the state (in whatever form that exists) says it is. The concept of the natural law has the advantage of being based on something immutable, though admittedly morality may differ somewhat from one society to another. The concept of natural law was first developed in the Greek world and has been carried through to the present day. There are a number of different approaches to this concept. The Graeco-Roman tradition held that there was a natural law that was accessible to mankind through reason. Christian theorists adopted aspects of Cicero’s Stoic philosophy, an example of natural law, because of its emphasis on moral content. The Christian legal philosophy that developed was in many ways a fusion between the fundamental Christian teachings and the adapted teachings of the Stoics. Natural law is the belief that there is a higher law than that of a government and that any law to be written by a government must be compared to and brought into line with natural law. This higher law is considered universally valid, and it is reached or perceived by the application of human reason.