To understand H.L.A. Hart's general theory of law, it is helpful to distinguish between substantive and methodological legal positivism. Substantive legal positivism is the view that there is no necessary connection between morality and the content of law. Methodological legal positivism is the view that legal theory can and should offer a normatively neutral description of a particular social phenomenon, namely law. Methodological positivism holds, we might say, not that there is no necessary connection between morality and law, but rather that there is no connection, necessary or otherwise, between morality and legal theory. The respective claims of substantive and methodological positivism are, at least on the surface, logically independent. Hobbes and Bentham employed normative methodologies to defend versions of substantive positivism, and in modern times Michael Moore has developed what can be regarded as a variant of methodological positivism to defend a theory of natural law.
Hart's Methodological Positivism