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Most people tend unreflectively to assume that laws belong to legal systems. "Most educated people," writes H. L. A. Hart, "have the idea that the laws in England form some sort of system, and that in France or the United States or Soviet Russia and, indeed, in almost every part of the world which is thought of as a separate 'country' there are legal systems which are broadly similar in structure in spite of important differences." This includes for most people the assumption that laws differ from non-legal rules and principles. There are, for example, moral rules and principles, social customs, constitutions and regulations of voluntary associations, and so on, which are not laws. Many legal philosophers have tried to justify this common assumption. Various criteria have been offered for demarcating the limits of law, for testing whether or not a particular standard belongs to a particular legal system. Various suggestions have been made concerning the importance of the distinction between what is legal and what is not, and the ways in which, by preserving it, we promote our understanding of law and society. For it has often been acknowledged that the distinction is not an easy one to draw in precise terms, and that any reasonable test would admit the presence of borderline cases. Despite these difficulties many theorists have thought that the distinction is worth preserving, partly because it is not difficult to apply in the majority of cases and partly because it seemed to them crucial for a proper understanding of law and society.
Joseph Raz (Sat,) studied this question.