The Greeks, and many subsequent thinkers, made the point that if conventional laws were grounded in natural law then rather than being mutable and arbitrary, they would be fair and just.
One sign of a law being "natural" is that it is universal rather than limited to one specific culture.
On the other hand, most people think that laws and conventions determining gender roles, such as the prohibition against females driving in Saudi Arabia, are purely conventional, as not only are they not universal but not grounded in the actual statistical evidence that female drivers are actually far safer than male drivers, getting in fewer accidents and getting fewer tickets.
Natural law and positive law differ in a number of ways.
The most important architects of this revised positivism are the Austrian jurist Hans Kelsen (1881-1973) and the two dominating figures in the analytic philosophy of law, H. Legal positivism's importance, however, is not confined to the philosophy of law.
It can be seen throughout social theory, particularly in the works of Marx, Weber, and Durkheim, and also (though here unwittingly) among many lawyers, including the American “legal realists” and most contemporary feminist scholars.157) The positivist thesis does not say that law's merits are unintelligible, unimportant, or peripheral to the philosophy of law.It says that they do not determine whether laws or legal systems .Thirdly, whereas natural laws are eternal and constant, positive laws can be amended or rescinded.Fourthly, natural law is based on reason and human beings have the free will to choose what they feel is right or wrong.For example, an overwhelming number of cultures have taboos against incest.Modern evolutionary biologists argue that these taboos are rooted in the natural laws of genetics, because incest or inbreeding is likely to increase the frequency of deleterious recessive genes.Its most important roots lie in the conventionalist political philosophies of Hobbes and Hume, and its first full elaboration is due to Jeremy Bentham (1748-1832) whose account Austin adopted, modified, and popularized.For much of the next century an amalgam of their views, according to which law is the command of a sovereign backed by force, dominated legal positivism and English philosophical reflection about law.Whether a society has a legal system depends on the presence of certain structures of governance, not on the extent to which it satisfies ideals of justice, democracy, or the rule of law.What laws are in force in that system depends on what social standards its officials recognize as authoritative; for example, legislative enactments, judicial decisions, or social customs.