This paper aims to show that the role that the principle of good faith plays in the construction of implied terms in contract law can be elaborated into more precise and concrete rules in statutory law, custom and precedents. This is to be established through a careful analysis of relevant statutory law, contractual usages and judicial decisions. To be sure, these sources are hierarchically ordered such that, facing a contractual gap, a judge must apply first statutory provisions and contractual usages, before relying on his own judicial powers to imply a contractual term. This means, it is contended, that when judges exercise their power to fill contractual gaps, they are also filling gaps in statutory law and, therefore, they are not only constructing a particular contract but contributing to the development of the law of contracts more generally.