The contractual obligations of the parties may be express or implied.
This provision restates the widely accepted principle according to which the obligations of the parties are not necessarily limited to that which has been expressly stipulated in the contract. Other obligations may be implicit (see Article 5.1.2, Comments and Illustrations).
Close links exist between this Article and some of the other provisions of the Principles. Thus Article 5.1.1 is a direct corollary of the rule according to which “[e]ach party must act in accordance with good faith and fair dealing in international trade” (Article 1.7). Insofar as the rules on interpretation (Chapter 4) provide criteria for filling lacunae (besides criteria for solving ambiguities), those rules may assist in determining the precise content of the contract and therefore in establishing the terms which must be considered as implied.