民事不當得利中損益間因果關係（確切地說是損益關連性）之論斷，向來是學說與實務上之重要爭議問題。直接因果關係說、非直接因果關係說或類型說等，於某程度上確實成功地解決了一部分因果關係的問題，然而，留下的困惑與爭議，只怕更多，就實務而言，似仍難擇一而為全面妥善適用。 本文認為當事人間財產損益之變動於事實面上是否存在著關連性，不是「有」，就是「沒有」，二者恆有一而且僅有一為真實，不因所得利益是否有法律上原因而有判斷上之差異。倘吾人能將損益關連性之判斷與「無法律上原因」要件之審查脫鉤處理，藉助充要條件遞移律之推理技巧，先客觀地建構出損益二結果事實間之邏輯關連性後，再進行「無法律上原因」要件之審查，應更能發揮「因果關係」一節於不當得利審查上之真正功能。文中雖輔以案例之操作初步證明本文觀點之可行性，惟其實用性與可接受性，仍待更多學說與實務之觀察與檢驗。

Our Civil Code §179 has ruled that three elements must be established to prove unjust enrichment, namely, loss and benefit, the causation in-between, and no legitimate explanatory basis. Among them, the causation inquiry is probably the most difficult and challenging task encountered in unjust enrichment actions, especially in multiple party payment litigations. Legal theorists and learned judges have devoted themselves to this topic in the heavily inked legal literatures and kinds of theories, such as direct causation theory, indirect causation theory, and disunity theory…etc. trying to frame practically sound principles only to achieve very limited success. This article, at the first place, hold that the concept of ”logic connection” should be substituted for the ”causation” element herein, since what actually bridging in-between the benefit and loss is not the matter of ”cause-and-consequence”, but would rather be the ”connection in fact” in nature. This article thereafter attempted to elucidate systemically the fundamental logic regulations and illustrate the way how they are manipulated in establishing the logic connection between benefit and loss, with special emphasis on the crucial application of ”transitive rule” in building up the logically concretely structured connection, which will definitely help to identify the party who really is enriched at the expense of another who's loss and thus grasp the unabridged integrated ”causation” element in proving unjust enrichment. This article also elucidated how the ”logic connection” approach could have easily and successfully been applied to prove unjust enrichment in complicated payment cases involving multiple parties. With cunning and appropriate application of logic regulations in the inquiry into the connection between benefit and loss, the actual situation can be easily and consistently clarified, and the restitution can properly be made. Only then can the fairness, equity and justice of jurisdiction finally be realized in unjust enrichment litigations.