As human behaviour is influenced by law, so law is influenced by human behaviour whenever the latter serves to bring about changes in existing legal situations. Law may be substituted for freedom of action; a regime of freedom may be restored where law prevailed; one set of rules may be succeeded by another set of rules. What are the kinds of human behaviour capable of so changing legal situations, and thereby entitled to the name “sources of law”? Here, an obvious distinction presents itself between material behaviour, and acts of communication with regard to future behaviour. A further classification would segregate mere acts of acceptance or rejection from positive behaviour contributing substance to the law. Let us illustrate these distinctions by examples from international relations.

As soon as fault—and hence, liability—is established on both sides, the owner who is faced with a suit, will try to constitute a fund in a country where he may keep alive his counterclaim—smaller than owner A's claim—, in a country with a “cross liabilities” system. The Convention opting for “single liability” will encourage such a desire for different fora and therefore the very aim of the Convention may well be thwarted.

In Soviet legal writings devoted to International Law of civil procedure it is taken for granted that the rules of the internal procedural law, which determine the local (territorial) competence of Soviet courts, function at the same time as rules which delimit international competence in civil law cases. Or as Marakov puts it: “En droit russe- en droit d'avant la révolution ainsi qu'en droit soviétique—la compétence générale coincide avec la compétence spéciale. Autrement dit, on étend les règles du droit interne de compétence spéciale aux rapports internationaux: en déterminant la compétence d'un tribunal de Moscou, on la délimite par rapport à la compétence du tribunaux d'Odessa ainsi que par rapport à la compétence des tribunaux de Berlin, de Paris, de Londres etc.”

The advent of the jet age has considerably increased the need, especially for smaller air carriers, to cooperate. Cooperation is a means to reduce the costs of airline operation and in this case it could facilitate the costly changeover to jet aircraft operations. At the same time cooperation can strengthen the competitive—and sometimes also the air policy—position of the partners. Interchange of aircraft is a modest form of interairline cooperation, which is primarily geared to rationalization of airline operation, i.e. to improve the efficiency of operation by meeting an aircraft shortage experienced by one partner, and by increasing the utilization of the aircraft of the other partner.