International commercial law conventions (or “transnational law”) increasingly have become the legal device of choice regulating international commercial transactions. These treaties contain substantive provisions that define the legal entitlements of parties to transactions within their scope. At the same time, they also mandate how the treaty’s text is to be interpreted. In particular, international commercial law conventions require that uniformity be taken into account in interpreting the text. UNCITRAL conventions, such as the CISG, are the most prominent example of these international commercial law conventions. An international convention, once ratified, displaces domestic law to the extent that domestic law is inconsistent with the convention’s provisions. But the incorporation of international commercial law conventions into domestic law has a further legal consequence. Its incorporation adds a method of textual interpretation for transnational law—"the uniformity directive”--to the methods in force in domestic law for the interpretation of treaties. As a result, the interpretation of transnational law texts relies on both generally applicable methods of treaty interpretation and interpretive methods specific to transnational instruments.
We maintain that international commercial conventions, once incorporated into domestic law, make legal interpretation more difficult and its results less predictable. Textual interpretation of transnational law is made more difficult not because transnational law introduces substantive rules into a legal system that differ from those of domestic law. Any incorporation of transnational law into national law does this. Instead, transnational law makes its interpretation more complex and less predictable because it introduces an interpretive method that differs from the methods for interpreting treaties generally. The increased difficulty in interpretation is exhibited in the tendency to rely on well-known domestic law methods to interpret transnational law.