Into the network of law
A legal system can be described as a network of rules (nodes) hierarchically linked and its evolution is a property of its network structure, Carlo Garbarino, professor of taxation at Università Bocconi, writes in the working paper A Model of Legal Systems as Evolutionary Networks: Normative Complexity and Self-Organization of Clusters of Rules. The paper applies network theory to model the structure and evolution of normative systems.
The model of legal systems as hierarchies of rules is based on the distinction between primary rules (directly aimed at individuals and establishing obligations or duties) and secondary rules (conferring normative powers to specific institutions). Some secondary rules are defined rules of production, when they establish a hierarchy between higher rules (e.g constitutional rules) and lower rules (e.g. statutes). In common law systems an important secondary rule is the "stare decisis" rule, according to which a subsequent court is bound to apply a precedent decision if certain requirements are met.
General rules are those created ex ante by institutions with proper powers and take form of statutes and regulations, while singular rules are created ex post by institutions with proper powers and are applicable to individual situations. Primary singular rules are called "Rules of the Case" and are the final nodes of production chains. Garbarino modelsnormative systems as sets of different types of rules which eventually lead to the production of Rules of the Case.
A formal hierarchy is defined by Garbarino as one established by a rule of production and occurs between a producing rule and a produced rule when the rule of production establishes how the second rule is produced by the first. Whenever a produced primary rule is derived from a producing primary rule according to a singular secondary rule of production there is a chain of production of primary rules. The links are always unidirectional from producing to produced rules, as the model represent a diachronic evolution of the network of nodes In legal networks which represent common law the subsequent cases are linked to the previous cases, like in citation networks or other social networks. The paper includes a set of network diagrams representing the application of statutes by courts and agencies, the creation of common law cases and self-compliance of rules by individuals.
The paper highlights that in the actual legal systems there are many Rules of the Case and a small number of main nodes generating such rules (these nodes are denominated "legal hubs"), as well as a high density of production links around these main nodes (leading common law cases or widely respected statutes). Garbarino thus identifies a concept of "normative complexity" which is represented as a network property of the system of rules. A modification of legal hubs has the deepest impact on the legal system represented as a network of rules.
Legal networks show three main forms of self-organization: the behaviour of courts under the "stare decisis" rule, self-compliance by individuals and enforcement by agencies and "because of these self-organization properties", Garbarino writes, "actual legal systems, viewed bottom-up in their constituent elements evidenced by network diagrams, are not centrally designed, even if in the higher echelons consist of statutes devised top-down to address policy issues".
The paper also shows that, as legal systems are modified over time (in the diachronic plane), there is an evolutionary structure of them which can be represented as a property of the legal network in different moments of time: there is so called "normative evolution" in the strict sense when Rules of the Case are added or eliminated, while there is so called "network evolution" when other kinds of rules which potentially lead to the creation of new Rules of the Case are added or eliminated.
In the final paragraph of the paper,Garbarino applies the network theory to the US tax system and indicates some interesting lines of empirical research which apply network theory to complex normative systems.