本文探討最高法院98年關於附隨義務及買賣物之瑕疵擔保與不完全給付競合關係之裁判。 附隨義務，來自於法律規定、契約約定及誠信原則。法官與學者之任務，在於闡釋立法意旨，探求締約目的，善用誠信原則，以認定附隨義務之存在與內涵。最高法院98年度有幾件判決，足供參照。應強調者，債務人雖履行其主給付義務，並不當然因而履行其附隨義務。就此，最高法院98年度裁判，有值得贊同者，亦有尚待商榷者。 依最高法院98年判決，債務人違反附隨義務者，債權人得依不完全給付而請求賠償或解除契約。請求賠償時，瑕疵給付之損害與加害給付之損害，均在賠償之範圍內。此外，附隨義務之請求權，亦有消滅時效之適用。 買賣物之瑕疵擔保與不完全給付之競合關係，在最高法院作成77年第7次民事庭會議決議後，實務上仍有甚多疑義。其中最具關鍵者為：（一）標的物之瑕疵於契約成立前業已存在者，出賣人固應負瑕疵擔保責任，惟買受人是否亦得併依不完全給付主張其權利？（二）標的物有物之瑕疵時，買受人依不完全給付主張權利者，有無民法關於瑕疵擔保規定（尤其民法第356條及第365條）之適用？ 關於第一個問題，最高法院98年判決結果歧異。本文則一貫認為，買賣標的物有物之瑕疵者，不論瑕疵發生於契約成立前或後，出賣人如因故意或過失而交付該標的物於買受人者，即應負不完全給付責任。 至於第二個問題，最高法院一直堅持：買賣標的物有瑕疵時，如買受人係依不完全給付規定主張權利者，民法第356 條及第365 條關於瑕疵擔保之規定，並無適用餘地。惟本文認為，為避免因買受人怠於檢查及通知，而不利於出賣人，民法第356 條關於買受人檢查與通知義務之規定，於買受人以物有瑕疵為依據，而依不完全給付解除契約時，亦應適用。

This paper scrutinizes 2009 Supreme Court decisions and rulings connected with collateral obligations as well as with the concurrent relationship between warranty for defects and incomplete performance in the case of sales contract. Collateral obligations can be derived from statutory provisions, contractual agreement and the principle of good faith. The duty of judges and legal writers is, by means of clarifying the purpose and object of the law, exploring the intention of the contract, and applying the principle of good faith, to perceive the presence and content of the collateral obligation. In this regard, several 2009 Supreme Court decisions are worth referring to. It should be noted that although the obligee has carried out performance of the main obligation, it cannot be concluded that the collateral obligation has also been fulfilled. In this respect, some 2009 Supreme Court decisions are worth approving, and some are not. According to the 2009 Supreme Court decisions, in the circumstances where the obligee violates the collateral obligation, the obligor is entitled to claim damages or terminate the contract pursuant to the provisions of incomplete performance. If damages are claimed, both loss pertaining to the non-conformity performance itself and consequential loss are recoverable. Furthermore, the cause of action based on breach of collateral obligation is also subject to statute of limitations. As to the problem of concurrence of warranty for defect and incomplete performance in the case of sales contract, the Supreme Court decisions remain disputable even after the announcement of the Supreme Court 1988 No. 7 Civil Court Resolution, particularly when the following two disputes are concerned. First, where defects of the object exist prior to the conclusion of the contract, can the buyer, though he/she is indubitably entitled to claim on the basis of warranty, resort to the provision of incomplete performance? Secondly, when the buyer bases his/her claims on incomplete performance, should such claims be constrained by the provisions of warranty (especially Articles 356 and 365 Civil Code)? Regarding the first issue, the 2009 Supreme Court decisions are contradictory. In the author’s opinion, no matter the defects exist prior to or posterior to the conclusion of the contract, the seller, who intentionally or negligently delivers the defective object to the buyer, should be held liable for incomplete performance. With regard to the second issue, the Supreme Court 2009 decisions persistently rule that in case the buyer asserts his/her rights under the provisions of incomplete performance, Articles 356 and 365 Civil Code are not applicable. However, in the author's opinion, in order to prevent the buyer from intentionally or negligently omitting to inspect the object and to notify, Article 356 Civil Code which relates to warranty and stipulates buyer's obligation to inspect and notify, is also applicable when the buyer terminates the contract in accordance with the provisions of incomplete performance.