論種類之債的履行不能──以種類物買賣為中心

On Impossibility of Performance of the Obligation in Kind: Focus on the Sale of Generic Goods

種類之債的客體具有不特定性，種類之債的債務人因而負有置辦義務，這是種類之債區別於特定之債的結構特徵。種類之債債務人是否構成履行不能，需要從當事人的契約約定和法律規定兩方面予以判斷。在契約約定方面，種類之債的當事人可以透過契約約定對債務人的置辦義務範圍進行限制，理論上透過區分市場型和非市場型種類之債，有助於更好地辨別債務人的置辦義務範圍。在法律規定方面，履行不能規則仍有適用的可能性。應根據種類之債當事人約定的置辦義務範圍，判斷種類之債債務人是否構成履行不能。

The subject matter of the obligation in kind is not specific, and the debtor under this type of obligation is therefore burdened with a duty of procurement. This duty constitutes a structural feature that distinguishes obligation in kind from the obligation in specie. Whether the debtor of the obligation in kind meets the conditions as to impossibility of performance, it needs to be assessed from two respects: the contractual agreement of the parties and the legal provisions of the Civil Code. From the perspective of contractual agreement, the scope of the duty of procurement can be contractually limited. At the theoretical level, distinguishing between market-based and non-market-based obligation in kind can help to better identify the scope of the debtor’s duty of procurement. From the perspective of legal provision, the rule of“impossibility of performance”still has room for application. At this point, the scope of the duty of procurement agreed by the relevant parties should be taken into account to assess whether the debtor’s duty of procurement can be fulfilled.