采用历史与比较方法分析买卖所涉及的两个问题。其一,买卖契约仅产生债的效力,抑或还直接产生物权效力;其二,物权变动是“要因”还是“无因”。罗马法及中世纪上,就合意性的买卖契约而言,它仅产生债的效力,所有权的移转须以交付为要件,这一点被以后的大多数国家所承继。而在同一时期,由于观念交付的出现,以及人文主义法学派的影响,买卖契约的物权性品格也有所体现。物权变动“要因主义”与“无因主义”在罗马文献上都得到印证。 Use history and comparative analysis of the two issues involved in trading. First, the sale and purchase contract only the effectiveness of the debt, or also directly produce the effectiveness of real rights; Second, the real right changes is “cause ” or “no cause ”. In the Roman law and in the Middle Ages, for the desirability of a contract of sale, it produced the effect of debt only, and the transfer of ownership had to be made on the basis of delivery, which was inherited by most later nations. During the same period, due to the emergence of concept delivery and the influence of the school of humanistic law, the real estate character of the sale and purchase contract was also reflected. The change of real rights “Essentialism ” and “No-cause ” have been confirmed in the Roman literature.