This thesis is the first legal sociological study that applies the concept of learning to the legal system. This thesis treats a national legal system as a learning system. The thesis contrasts with the dominating tradition that emphasises the assumption that law is a system of norms. As a system of norms law is frequently described in terms of its static qualities. This type of legal sociology often reduces the legal system to a form of control with little self-determination or autonomy. Therefore the definition of legal concepts has been seen as a relatively unimportant and strictly legal affair. As a contrast this thesis shows how prerequisites for legal change are determined by the definition of basic legal concepts. One conceptual development process is investigated. The evolution of legal personality in German legal theory is followed historically from the 18th to the 20th century. The form of this development process is shown to support several observations of legal learning. It is shown that law learns by developing images of its environment framed in its concepts. The internal images of the environment of law make further learning possible. The evolution of modern law of associations is shown to encompass such a learning process. Law is also shown to learn by identifying and solving paradoxes in its internal structures. The identification and handling of paradoxes is shown to determine the ability of the legal system to change when its environment changes.