Kramer explains how H. L. A. Hart reinvigorated legal positivism by disconnecting it from the command theory of law defended by his predecessors Bentham and Austin; by introducing through his own theory of law some new and fruitful concepts into legal thinking, such as the internal point of view, the distinction between primary and secondary rules, and the idea of a rule of recognition; by clarifying the meaning of and reasons behind the separability of law and morality through considering the many different ways in which law and morality are, or could be, connected; and by introducing the idea of the minimum content of natural law and clarifying the relation between this and the separability of law and morality. Kramer explains: even though a legal system can fulfil its basic function of securing the conditions of civilisation only if it includes rules prohibiting murder, assault, fraud, etc., the relevant protection provided by the legal system against such misconduct need not be extended to all groups of citizens. Consequently, because no true moral principles would permit this, Hart’s account does not reveal any necessary connections between those principles and legal norms.