The basic realisation of the Legal Positivist movement was that what the law is and what it ought to be are separate. The champion of this perspective was John Austin. The origins of Legal Positivism will be described, as will the importance of the Social and Separation theses. Critiques of the Legal Positivist stance will also be briefly considered.
Austin's importance to legal theory lies in his theorising about law; he discussed the law at three different levels. Firstly, he was amongst the first people to adopt an analytical approach to Law. This was in sharp contrast to those who argued from sociological or historical perspectives, or presented their analyses of law as secondary to moral or political considerations. Although this analytical approach to jurisprudence has been criticised , it has been for some time the dominant method for the analysis of the nature of Law. Secondly, Austin was key to the genesis of the Command Theory of Law. Linked to this is his third contribution—the formulation of the Legal Positivist approach to Law.
Most of the pre-Positivist writing on law prior to Austin had treated jurisprudence as though it were merely a branch of moral philosophy or political theory. These enquiries related to the method of governance of governments, and the legitimacy thereof. Also considered were the circumstances under which one must obey the law. Austin specifically, and Legal Positivism generally, offered a markedly different approach. As with other areas of human endeavour, such as the examination of the natural world, Austin believed that Law could become the province of proper and true scientific enquiry. Such a systematic approach to law gained popularity in the late 19th century, especially amongst lawyers who wanted to approach their profession, and their professional training, in a more serious, rigorous, and ‘scientific’ manner .
Legal positivism asserts that it is both possible and valuable to have a morally neutral descriptive theory of law. The contemporary competitor to such a perspective was one derivative of Natural Law, one that is antithetical to a Positivist line of argument. It is important to note that Legal Positivism does not deny that moral and political criticism of legal systems is important. It insists, however, that an empirical descriptive approach to law is valuable is a necessary precursor to such criticism. The simplest exposition of this argument is found in Austin's writing:
The existence of law is one thing; its merit or demerit is another. Whether it be or be not is one enquiry; whether it be or be not conformable to an assumed standard, is a different enquiry. A law, which actually exists, is a law, though we happen to dislike it, or though it vary from the text, by which we regulate our approbation and disapprobation.There were theorists prior to Austin who arguably offered views similar to legal positivism or who at least foreshadowed legal positivism in some way. Among these would be Thomas Hobbes, with his amoral view of laws as the product of Leviathan . Also of importance is David Hume, with his argument for the ‘is / ought’ cleavage , and Jeremy Bentham , with his attacks on judicial lawmaking. One target of Bentham's scorn was Sir William Blackstone, who justified such lawmaking with natural-law-like justifications.Austin (1832) 
The general theme of Austin's writing was the determination of what could be said generally about law beyond the level of mere truisms. Austin's analysis can be seen as either a paradigm, or a caricature of, analytical philosophy. Certain commentators suggest argue such as his discussions are full of dry distinctions, but are thin in argument .
The general tenor of his writings is that the nature of law is fundamentally that which the sovereign commands. This concept of positive law is contrasted with similar ideas :
Within Austin's approach, whether something is or is not ‘law’ depends on observable action—it is a question of empirical observation rather than morality. That is not to say that an Austinian view has normative amoral implications, or that it describes law as being amoral. It is, however, pointing out that there is more to law than simply a question of morality. The end result of Austin's recognition criteria of law, then, is to base the determination of validity on external social facts rather than an intrinsic moral element. This relies on two separate claims: the Social thesis, and the Separation thesis.
The Social thesis asserts that Law is fundamentally a social construction. Early Positivists saw this in terms of the Hobbesian view of Law as power. Law is the command of the sovereign. It follows then that this power is derivative of the social factors that determine political sovereignty. Later Positivists have modified this perspective, stressing the importance of social aspects at the expense of the primacy of the sovereign. As the Logical Positivist tradition has progressed, so has the sophistication of the concept of the sovereign. Most contemporary legal Positivists share the view that there are conventional rules of recognition. These are social conventions that determine certain facts or events that provide the ways for the creation, modification, and annulment of legal standards. These facts, such as an act of legislation or a judicial decision, are the sources of law conventionally identified as such in each and every modern legal system.
Natural Law theorists deny this insight, insisting that a putative norm cannot become legally valid unless it passes a certain threshold of morality. For supporters of Natural Law, morality acts as a threshold device for the approval of new law. The moral content of a law, not just its social origins, determine its legal validity.
The Separation thesis comes on the heels of the Social thesis. It maintains that, as the titular quote suggests, Law and Morality are separate; that there is a conceptual divide between what the Law is and what the Law ought to be. It is not the case that ‘Natural Law asserts and Legal Positivism denies’  any normative content to the law. The Social thesis does not necessarily hold moral content of Law as false; merely that law is a societal construct. Nor does it deny the moral content of law—indeed there is quite probably an appreciable overlap between law and morality. However, such overlap is not properly the concern of a Legal Positivist; it is simply happy coincidence. The difference between a Natural Law approach and a Legal Positivist approach is one of perspective—Legal Positivism pertains only to the conditions in which laws are recognised as laws. It makes no secondary claims about the value of such law; what the law is cannot relate to what it ought to be.
An intermediate position between Legal Positivism and the Natural Law tradition has been adopted by the Inclusive Legal Positivists. Whilst they endorse the Social aspect of legal validity, they question the Separationist aspect. Those social conventions on the basis of which one identifies the law may, but need not, contain reference to moral content as a condition of legality .
The Natural Law tradition of Natural Legal has undergone considerable refinement in the 20th century. The idea that all law must necessarily pass a kind of a moral filter before it can be accepted as proper law is, I find unappealing. Different authors have suggested more subtle interpretations. John Finnis does not regard Natural Law as a constraint on the legal validity of positive laws. Instead, it mainly functions as hermeneutic of an ideal form of law, concentrating on the ways in which law necessarily promotes the common good .
Austin's views are not without fault. Indeed, numerous critiques have been made, and continue to be made, of this perspective. It has been argued that such an approach is reductionist, power-obsessed, and inaccurate.
It also becomes necessary to consider what happens when ‘the laws run out’; this is the province of Dworkin's Hercules. A Positivist would argue that the law does not resolve the issue either way. Instead, the decision must be resolved either by new legislation or judicial discretion. This is because, from a Positivist's perspective, the law as it stands is only what past authoritative statements or conventions have declared it to be. By definition, these ‘hard cases’ have not been settled in any previous decision or legislation, or they would not still be problematic. More radical legal philosophers, such as the American Legal Realists and Critical Legal theoreticians follow a similar path. They argue that there is never a right answer to a legal question, because past legal doctrine is not sufficiently consistent to yield a single result. But Judges, at least in Anglo-American law, never refuse to decide a legal dispute on the ground that the law is indeterminate, and rarely claim to be exercising a discretion to create new law and apply it retroactively. Even in very controversial cases they give answers to the questions of law in dispute which they claim to be, at least in their opinion, the right ones .
To reduce law to a single punishment-enforced type necessarily distorts one's perspective. Granted, the application of sanctions describes certain aspects of the law very well, with criminal law being a prime example. The problem is with laws meant to empower rather than punish. Whilst it is possible to conceive of such laws as a long handed method of the imposition of a sanction (Austin spoke of nullity as a punishment), it is to ignore the fact that such laws are about granting power, not retaining it. When Hart reinterpreted legal positivism, he did so by building on the above critiques. He made the distinction between various types of rules .
The Procrustean characterisation of all ‘valid’ law as being derivative of a sovereign fails to take into account a number of important branches of the law, most notably Public International Law. An anarchic system (without a leader as opposed to chaotic) by Austin's definition is incapable of having laws.
Additionally, a theory of law that fundamentally equates law with power will necessarily fail to distinguish the arbitrary rules of a dictator based on terror from those of a legitimate government. Admittedly, such distinction necessarily begins to wander into the realms of political theory. However, if one has any kind of normative view of the role of the Law, it becomes a necessary component of the maintenance or change of society.
Also worthy of consideration is the notion of the sovereign. Austin himself encountered this difficulty in describing the British sovereign as a combination of the King, the House of Lords, and all the electors of the House of Commons. Additionally, a focus on the sovereign makes it difficult to explain the continuity of legal systems: a new ruler will not come in with the kind of ‘habit of obedience’ that Austin sets as a criterion for a system's rule-maker. Arguably, the sovereign represents a constructive metaphor . Kelsen would call such a metaphor the grundnorm. Dworkin would perhaps see the sovereign as another name for the collective will of the law-as-integrity .
The recognition of the distinction between what the law is and what it ought to be is amongst the most important contributions made to legal philosophy. Although now it can perhaps be regarded as something flawed and inadequate, Austin's work was at the time revolutionary. It transformed our understanding of the very nature of Law. Such a paradigmatic shift in jurisprudence allowed for the development of increasingly sophisticated conceptualisations of what law is, and its relation to what it ought to be.