論條件的溯及效力與即時效力

條件是否具有溯及力是民法上的一個傳統問題。在附條件處分中，條件具有溯及力的，附條件權利人能夠自始取得物權，並在未決期間內享有物權性保護（直接保護）。附條件權利人在未決期間處分標的物的，處分能夠溯及至條件成就前生效（間接保護）。條件的溯及力會在履行返還、孳息歸屬和當事人權責等方面引起一些不當法律後果。條件的即時效力能夠避免前述不當後果，但附條件權利人無法享有直接保護與間接保護。現行法在承認條件即時效力時，有必要設立一個特殊保護機制，配置期間處分無效規則，以確保附條件權利人能夠正常取得物權。附條件權利人的利益是否構成期待權，取決於條件成就的可能性、法律保護的強度、社會經濟之需求，不能一概而論。當前而言，法律應當承認所有權保留中的買受人與附條件遺囑中的後位繼承人享有期待權。

The retroactive effect of conditions is a conventional issue in private law. In the situation of conditional disposal, this effect allows the conditional right-holder to acquire the property right ex tunc and to enjoy proprietary protection during the pending period (direct protection). If the right-holder disposes of the object in the pending period, this disposal can take effect before the fulfilment of the condition (indirect protection). However, the retroactive effect gives rise to undesirable consequences in some circumstances, including the recovery of the performance, the allocation of the fruits, and the parties' rights and liabilities. The immediate effect of conditions can avert these undesirable consequences, but both the direct and the indirect protection would be unavailable to the conditional right-holder. The applicable law recognizes the immediate effect of conditions. Therefore, it is necessary to have a special regime of protection by recognizing invalidity of disposal in the pending period for the benefit of the conditional right-holder, so that he or she is able to acquire the object without being interfered with. The qualification of the conditional right as a right of expectation depends on the possibility of fulfillment of the condition, the legal protection recognized, and the social-economic demand. Nowadays, it is desirable to recognize that the buyer under the reservation of ownership and the subsequent successor in the situation of subsequent succession enjoy a right of expectation.