约因是英美法中的特有概念,在我国的合同法语境中,对约因的理解有时不够准确。文章从约因的历史发展上梳理了约因的起源和经典案例,进而分析了其具有的证据功能、警示功能、保证功能。约因本身是诉讼形式遗留的产物,但它所提供的外观实际上成为缔约当事人之间的引导者,这可为我国今天的合同法起到一定的借鉴意义。 About reason is the unique concept of Anglo-American law. In the context of contract law of our country, the understanding of the cause of death is sometimes not accurate enough. The article combs the origin and the classic case of Joyin from the historical development of Join, and then analyzes its evidence function, warning function and guarantee function. The contract itself is the legacy of litigation, but the appearance it provides actually acts as a guide between the contracting parties, which can be used as a reference for our country’s contract law today.