In speaking of statutory law in the common law courts, lawyers have ascribed to it a limiting office, namely, that of interference with the parties' freedom to act and transact at their pleasure. A closer consideration shows them that the function of statutory law varies not only with the legal system to which it belongs, but also with the structural changes within a single legal system.
OPTIONAL TERMS (JUS DISPOSITIVUM) AND REQUIRED TERMS (JUS COGENS) IN THE LAW OF CONTRACTS,
Mich. L. Rev.
Available at: https://repository.law.umich.edu/mlr/vol45/iss1/3