The purpose of a legal system is to provide a systematic, orderly, and predictable mechanism for resolving disagreements. The judicial function is the core of any legal system. In its judicial function, a legal system adjudicates disputes, issuing a decision as to how the disagreement should be settled. The other two functions are merely adjuncts to this central function. The purpose of the legislative function is to determine the rules that will govern the process of adjudication.
Legislation tells judicial function how to adjudicate.
Finally, the purpose of the executive function is to ensure, first, that the disputing parties submit to adjudication in the first place, and second, that they actually comply with the settlement eventually reached through the judicial process. In its executive function the legal system may rely on coercive force, voluntary social sanctions, or some combination of the two. The three functions of law are monopolized by a single agency, but distributed among distinct groups of decision-makers within that agency. The three functions of law are not monopolized. Various combinations of these are possible, since there are legal systems under which some functions are monopolised while others are not.