Basically, natural law is the system of law based on human nature. That means that the law is determined by intrinsic values in human nature and can be deduced independently of positive law.
Several versions of legal positivism include a theory of separability in its foundations. This theory is part of the basis of legal positivism and asserts that law and morality are conceptually distinct. This is a response to the traditional notion of natural law, in which both law and morality are normative systems. It aims to explain how the distinction can be made between them, thereby solving the problem of jurisprudential antinomy.
A common interpretation of the separability thesis is that law and morality are distinct in the sense that law and morality cannot be conceived of in the same way. This can be understood in a number of ways. It can be interpreted as a general claim that law and morality are separate from one another, or it can be interpreted as a more narrow claim that law has moral value.
In a more complex understanding of the separability thesis, it is argued that a system of rules has no morally valuable objectives unless it meets certain legal requirements. This explains why no system of rules can achieve such objectives without minimal compliance with legality. It also explains why no system of rules can have a morally good effect without a moral component.
Various authors have criticized the separability thesis, arguing that the thesis fails to recognize the nature of law and morality. Hart, for example, claimed that legal reasoning was not moral and that it was normative. Nevertheless, it seems that the separation thesis is a conceptually valid assertion.
Those who believe in the commonsensical implications of natural law have argued that natural law is a moral standard that is known by human reason. Many conservatives have claimed that it supports traditional morality and social order. Others have argued that it is grounded in biological processes. There are, however, disagreements about whether or not natural law is a universal or particularistic principle.
For instance, one of the commonsensical implications of natural law is that it is inherent within the nature of humans. Some believe that it is passed on through divine influence. Other schools of thought, such as those in the sociobiology and evolutionary psychology communities, have applied Darwinian biology to human nature. These perspectives are sometimes called neo-Darwinian.
Another commonsensical implication of natural law is that it supports self-preservation. For example, almost all people accept that murder is a punishable offense. It is also accepted that child care should be provided.
Yet a third commonsensical implication of natural laws is that they support social order. For instance, rape and sexual differences are deemed acceptable, but the penal code punishes certain crimes. The problem with this approach is that there are too many rules that are not morally good. Therefore, judges should not ignore the moral reasonableness of derived rules.
In response to these challenges, John Crowe argues that law is an artifact. He explains why moral defects of rule relate to legality.