This thesis addresses the historic debate between natural law theorists and positivists. After providing a foundation for the debate by discussing the thirteenth century natural law theory of St. Thomas Aquinas and the criticisms of it by positivist philosopher John Austin, this thesis turns to the theory of H.L.A. Hart. My primary aim is to outline a defense of the soft positivism of H.L.A. Hart in face of the criticisms of Ronald Dworkin by appealing to two nonexclusive roots of moral principles in the law: justice and criminal law.