What is law

The existence of law means that certain kinds of human conduct are no longer optional, but in some sense obligatory. Obligation is the essence of law. How do law and legal obligation differ from, and how are they related to, orders backed by threats.

Just as a legal system obviously contains elements closely connected with the simple cases of orders backed by threats, so equally obviously it contains elements closely connected with certain aspects of morality.

Law is better understood as a 'branch' of morality or justice and that its congruence with the principles of morality or justice rather than its incorporation of orders and threats is of its 'essence'. But theories that make this close assimilation of law to morality seem, in the end, often to confuse one kind of obligatory conduct with another, and to leave insufficient room for differences in kind between legal and moral rules and for divergences in their requirements.

Both those who have found the key to the understanding of law in the notion of orders backed by threats, and those who have found it in its relation to morality or justice, alike speak of law as containing, if not consisting largely of, rules. But what are rules? What does it mean to say that a rule exists?

It is to say that a rule exists means only that a group of people, or most of them, behave ' as a rule' in a specified similar way in certain kinds of circumstances. But mere convergence in behavior between members of a social group may exist and yet there may be no rule requiring it. 

Three recurrent issues:
(1) How does law differ from and how is it related to orders backed by threats?
(2) How does legal obligation differ from, and how is it related to, moral obligation?
(3) What are rules and to what extent is law an affair of rules?
Solve these problems to decipher the 'nature' of the law.