MacCormick's classification, consisting of institutive rules, consequential rules, and terminative rules of legal institutions, is extended with three additional classes, namely, constitutive rules, content rules and invalidating rules. A test shows that complete legislation constituting a certain class of legal institution contains rules of all distinguished classes. Legislation takes place by appeal to power-conferring rules that form part of a legal institution. Modern legal systems are characterized as nested sets of legal institutions that are connected by the exercise of power-conferring rules. The component parts of legal institutions are classified.
Attention is paid to the manner in which legal institutions are socially accepted.
Lagerspetz's conventionalist method of grounding the social existence of legal institutions on shared beliefs is critically examined and rejected. It is concluded that the classical idea that legislation would mainly consist of general rules of conduct is far too simplistic. Modern legislation rather serves to present images of overall institutional environments that exert pressure to be socially realized. Legislation has become a form of institutional landscaping in which legal institutions of different classes are combined to provide fitting institutional environments. Finally, a classification of legal institutions is proposed on the basis of a fourfold distinction between subjects, objects, properties and relations.