本文以一則工程契約判決為例，探討契約定性的概念及功能，並檢視當契約出現漏洞時，法院究竟應適用（或類推適用）「任意規定」或採取「補充的契約解釋」以填補漏洞？由於工程契約具有特定性投資等特性，不宜機械性套用民法有關承攬之任意規定；此外依「繼續性」或「接續性」之有無，以判斷當事人得否「終止」或「解除」契約之見解，亦待檢討；從而本則判決理由與結論，均有不當。為避免削足適履之弊，契約定性允宜審慎，必要時不妨予以「相對化」。以本則判決為例，工程契約究應定性為承攬契約或非典型契約？本屬仁智互見。即使將之定性為承攬契約，法院仍應採目的性限縮之解釋方法，考量適用任意規定之適切性，限縮其適用範圍；再考量經濟效率、公平正義、工程實務與比較法制等因素，透過補充的契約解釋，賦予上訴人得終止契約（而非僅得解除）之權，如此方符合契約法真諦，文末並呼籲檢討以往過於仰賴契約類型與任意規定之缺失。

This article critically examines a recent Supreme Court's decision of a construction dispute and argues for a new approach in dealing with gaps in contract. Conventional judicial approach in contractual dispute usually involves the initial determination of which ”statutory contract type” as defined in the Civil Code does the contract in dispute fall into, and the subsequent mechanical application of the corresponding set of default rules associated with the contract type. However, since current default rules are incompatible to the commercial characteristics and purposes of modern construction contracts, a court should exercise great caution in mechanically applying these rules, particularly the rules on termination. In the present case, the Supreme Court erred in applying a default rule that denied the contractor a right to terminate the contract without the obligation to restore the unfinished work to its original condition. Rather, in light of considerations such as economic efficiency, fairness, trade customs and comparative law, the court should focus more on the purpose and function of the law of contract when filling gaps, rather than simply electing to mechanically determine contract type and apply its default rules.