ABSTRACT
This chapter examines in more detail how courts interpret and apply non-state rules as a source of domestic law. It analyses the example of trade usages under two instruments: the UCC and the CISG. Trade usages are an important source of domestic law in many jurisdictions. They can be used either to add additional terms to the contract or to interpret the contract. Trade usages are born out of the practices of merchants and their existence is confirmed based on observation by the courts. Both the UCC and the CISG strongly favour trade usages and they will be applied before variable provisions of the legislation. This chapter discusses whether codified non-state rules can be applied as trade usages under the UCC and the CISG. The conclusion is that this is possible, especially for the Incoterms. The UNIDROIT Principles are also applied as trade usages, more frequently under the CISG than under the UCC. Overall, this usage remains modest. The chapter thus demonstrates that whilst the role of non-state rules in private international law is more limited, their role as a source in domestic law can be significant.
