In the field of legal philosophy thinkers attempt to define things like law and the legal system.  For centuries law was seen solely as a kind of social control marked by a linkage between the law of men and the moral authority of a perceived higher power.  This line of thought, which says there is an essential connection between morality and law, is known as natural law.  The study of the philosophy of law has transitioned away from this idea of natural law to what is called legal positivism.  This idea, along with Hart’s idea of a legal system marked by the union of primary and secondary rules provide much room for a good introduction into the evolution of legal philosophy. 

            Through the nineteenth century the idea of legal positivism, one that challenged the prevailing idea of natural law, was advocated by John Austin.  This philosophy’s unique characteristic was the fact that it separated the moral from the legal.  The law, under this system of thought, was simply the law.  As modern states began, the idea of men making law of and for themselves, and without God’s sanction, was seen as an acceptable way of creating public policy.  The higher power normally associated with God was now given also to man.

Austin defined law in this kind of legal system as a command, or wish for something to be done.  This command was backed by the threat of something bad, or “evil,” happening to the citizen who did not do abide by the command.  In this system there are general commands, or rules that apply to everyone, and most rules are followed simply by force of habit.  The benefits of these habits fall at the feet of the sovereign.  This person gets to reap the benefits of the population’s adherence to the rules, while generally not having to follow the same guidelines. 

            In the twentieth century H.L.A. Hart challenged Austin’s view of the positivist legal system.  While Hart did not seek to refute the most basic tenet of legal positivism, that being that there is a separation between the legal and the moral, he did call into question many of the characteristics Austin’s idea of the law ascribed to.  Hart is critical of the fact that according to Austin, a law does not have to be followed by the sovereign.  The modern state provides many examples of why even the sovereign must obey laws.  Another sovereign-related problem Hart cites in Austin is the legal powers of the individual that are ignored, such as contracts.  Common citizens can enter into legally binding agreements that do not much involve the sovereign.  A key tenet of Hart’s criticism is the role of the sovereign in relation to the rules of a society.

            The creation of law is a different area where Hart finds he is able to criticize Austin.  Austin ignores the fact that in some legal systems, law is based on custom, or what has passed before.  This kind of common law tradition is not set by the rulers but instead ingrained in society through years of evolution.  Along these same lines Austin, according to Hart, fails to explain how laws continue.  If there is not any tradition or custom for keeping or discarding rules, what happens when the sovereign dies?  In Austin all rules would pass away because there would be no way to allow the succession of another ruler.  In a broad sense, Hart argues that Austin’s assertion that orders, obedience, habits, and threats simply do not add up to a clear definition of law or a legal system.

            Hart’s notion of a rule is marked by the mix of what he calls primary and secondary rules.  Primary rules are those that direct duties.  Secondary rules give powers to do a great variety of things based on the primary rules.  These rules allow those in a legal system to change or create legal relationships.  This is quite a bit more complex than Austin’s idea of law, which Hart seems to argue does only a good job of defining primary rules. 

            Hart’s demonstrates how his idea of the union of primary and secondary rules better explains the complexities of a legal system through his the example of the gunman.  If a gunman holds me up at the teller machine, am I obligated to give him the money?  It is a command backed by a threat, but I am not obligated to give the gunman anything.  Hart argues that I would be obliged to give the man the money but certainly not obligated to do so. 

            The example of the gunman points to one of the key parts of Hart’s theory of law.  This is that the threat of evil is not the most central part of the rule.  Rules depend much more on their legitimacy.  We follow the rules of society because they were equitably decided upon by our own representatives, not solely (or even mostly) because we will be punished if we do not comply.  This does call into question Hart’s position as a legal positivist as he appears to be mixing the moral and the legal.  In response to this Hart argues that the rules are only normative from an internal view of a legal system.  Once outside the confines of the society the separation between the legal and the moral is still sensed, according to him.

            The example of the gunman also shows how a legal system based solely on primary rules of obligation, as Austin’s seems to be, is no legal system at all.  Hart argues that there is an element of human nature that leads us to the establishment of primary rules to guard against violence and eminent danger.  These rules do not make up a comprehensive system.  Instead they are just several independent rules that do not bear on each other.  This creates several problems for a basic system such as this.  No one is sure how to resolve disputes and it is unclear how to make a new rule or change a bad one.  This kind of system leads to a society of revenge, vendetta, and general social chaos.

            This point of chaos is where secondary rules come in and save the day.  A legal society will possess these rules that allow it to get through the difficult and uncertain times of controversy.  These rules build off of the primary ones forming a network that allow the system to change and react to the stresses of technology and controversy that are put on it.  These rules solve the uncertainty of a pre-legal society by providing a way for rules to be changed, for disputes to be resolved, and for individual legal relationships to be varied.  Secondary rules allow an easy answer for who possessed the authority in society, who changes rules in society, and who decides how things will be executed.

            Within this vast network of secondary rules there can exist, from time to time, a question as to whether a rule is valid or not.  What gives a rule validation?  This is a difficult question to answer especially given the view of legal positivism, which asserts that moral force is not the source.  Every legal system has what is called a special rule of recognition.  This supreme rule determines where all legal authority originates.  Those in the legal system must agree on this rule if the system is to continue.

            An example of this principle is shown by the chain of rules that ends in the ultimate or supreme rule.  For example, a primary rule exists that says one may not park in front of a fire hydrant.  The authority of this rule can be traced all the way back to the United States Consititution, which gets its authority only from the fact that most all people agree that it is legitimate.  If we did not realize the base validity of the constitution then the network of our legal system would begin to crumble. 

            Legal positivism seems to be in good hands with the ideas of Hart.  The course of thought seems in much better intellectual shape than it was when it only consisted of the basic primary rule-based assertions of Austin.  That basic system did not explain a legal system fully as it ignored many of the basic tenets of a legal society.  With Hart’s explanation, though we see the line thinning between the moral and the legal, we are able to better understand how the intertwining authority of secondary rules, built off of directing primary rules, allow for the legal world to continue spinning.