Private law sources in international law were a main object of study of Sir Hersch Lauterpacht, who is considered one of the greatest international lawyers of the last century. In his time, the International Institute for the Unification of Private Law’s Principles of International Commercial Contracts (PICC) did not exist. The first version of the PICC was only published in 1994, more than three decades after his death. In the year 2000, the disputing parties of an investment treaty arbitration case concluded before a tribunal chaired by his son, Sir Elihu Lauterpacht, a settlement agreement dated 20 March 2000, which would later be embodied in an International Centre for Settlement of Investment Disputes Additional Facility arbitral award issued by the tribunal on 18 September 2000, where they incorporated slightly modified PICC provisions. The present article will argue that private law sources are still important in certain areas of international law, such as investment arbitration. In investment arbitration, they are not only important in presence of contracts but they can also arguably be useful for the interpretation of treaties. Investment tribunals have indeed recognized the importance of the PICC for both the interpretation of contracts (transnational agreements) and the interpretation of treaties (international agreements).

中文翻译：

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Hersch 和 Elihu Lauterpacht 以及私法渊源与国际法的相关性：在国际法演变和统法协会原则采纳的背景下从理论到实践

国际法中的私法渊源是 Hersch Lauterpacht 爵士研究的主要对象，他被认为是上世纪最伟大的国际律师之一。在他那个时代，国际统一私法协会的国际商事合同原则（PICC）并不存在。PICC 的第一版是在他去世三十多年后的 1994 年才出版的。2000 年，投资条约仲裁案的争议双方在其儿子 Elihu Lauterpacht 爵士主持的法庭上缔结了一份日期为 2000 年 3 月 20 日的和解协议，该协议后来体现在国际投资争端解决中心仲裁庭于 2000 年 9 月 18 日发布的便利仲裁裁决，其中纳入了略微修改的 PICC 条款。本文将论证私法渊源在国际法的某些领域仍然很重要，例如投资仲裁。在投资仲裁中，它们不仅在存在合同时很重要，而且可以说对条约的解释很有用。投资法庭确实已经认识到 PICC 对合同解释（跨国协议）和条约解释（国际协议）的重要性。