q EJIL 2000 ............................................................................................. The Internationalist as a Scientist and Herald: Lassa Oppenheim Mathias Schmoeckel* Abstract Lassa Oppenheim’s treatise has been called ‘probably the most influential English textbook of international law’. Its comprehensiveness invited several great internationalists to re-edit the book. But the original intentions of the book, as well as Oppenheim’s biography, have not yet been closely investigated. The German-born Oppenheim, professor of criminal law at the University of Basel, focused on international law only after his move to London in 1895. Though naturalized in 1900, his views on law remained influenced by the German methodological discussion of that period, generally labelled as ‘positivism’. Looking at this discussion more closely, different approaches to ‘positivism’ can be identified. There is Oppenheim’s originality as well in so far as he also drew on contemporary psychological theories of law. Thanks to his clear and consistent ideas on method, Oppenheim could reduce the existing doctrinal theories to a seemingly homogeneous body of law. Oppenheim was convinced that such a description would stimulate the spread of the knowledge of international law and thus further international understanding. The modernity of Oppenheim’s book is due both to his psychological and his systematic approach. While Oppenheim wrote at the end of the classical period of international law his textbook has become, in its turn, a classic like the work of Grotius. 1 The Man and the Book Lassa Oppenheim was born at Windecken near Frankfurt-am-Main in 1858 and died at Cambridge shortly after the First World War in October 1919.1 His father was a Jewish horse trader who achieved considerable wealth and the family moved to Frankfurt where they lived from private means. His education was remarkably * University of Bonn. 1 See M. Kingreen, Jüdisches Landleben in Windecken, Ostheim und Heldenbergen (1994), at 112–114; Zimmermann, ‘Oppenheim, Lassa Francis Lawrence’, in Neue Deutsche Biographie, vol. 19 (1999), at 566–567. .............................................................................................................................................................. EJIL (2000), Vol. 11 No. 3, 699–712 700 EJIL 11 (2000), 699–712 extensive. In 1878 he began his law studies, but followed courses in metaphysics with the philosopher Hermann Lotze, psychology with Wilhelm Wundt, and legal medicine in order to gain a thorough understanding of jurisprudence. He studied in Göttingen, where he learnt Roman law with Rudolf von Jhering, in Berlin, where he heard amongst others Julius Baron, Heinrich Brunner, Georg Beseler and the great historian Heinrich von Treitschke, and in Heidelberg, where he followed Caspar Bluntschli’s course in international law. In Göttingen in 1881 he handed in his doctoral dissertation which he had written under the guidance of the famous commercial lawyer Heinrich Thöl. This is an impressive list of some of the most prominent German lawyers of the time. After a short period of practical experience he determined on an academic career and on criminal law as his major subject. He was one of the true pupils of the famous criminal lawyer Karl Binding in Leipzig. In this field they influenced each other. His ‘Habilitation’ took place in Freiburg in 1885. At this time Baden was the most liberal part of Germany in appointing Jews to university chairs. Here he hoped to receive a professorship. By the beginning of the 1890s he had published five books on criminal law and some articles. He was appointed Extraordinarius Professor in 1889 in Freiburg, but contrary to his expectations he did not receive an ordinary professorship. For this reason he moved to Basel in 1892 as an extraordinary professor and was made ordinary professor in 1893. This could have been an end to his career. But British relatives, liberal inclinations, financial independence and perhaps a propensity for the British way of life induced him to leave his job and to move to London in 1895 without any prospects of another income. But he adapted quickly and was naturalized on 31 December 1900, by which date and act he became Lassa Francis Lawrence Oppenheim; his father had called him Lahsa. In London he had to start a completely new career and chose international law as his new field. He quickly gained expertise and built up a vast library. Even the Foreign Office started to borrow books shortly after his naturalization. This shows the extent to which his father’s inheritance had made him financially independent. Such private means made life easier to some degree and explain part of Oppenheim’s life. Nonetheless, he began teaching again as soon as possible. He first taught in night schools, then at the London School of Economics. With the publication of his International Law (the first edition was published in 1905–1906), he gained a high reputation in England and abroad. Due to John Westlake’s recommendation he was appointed as professor of international law at Cambridge University in 1908. He thus became the fourth Whewell Professor. He held this chair until his death in October 1919. His International Law proved to be an unusual success. It sold extremely well in its first three editions. The third edition was completed after his death by Oppenheim’s student Roxburgh, who stuck closely to the ideas of Oppenheim. In 1919 Oppenheim was still able to rewrite considerable parts of his book and to comment on the new evolution of international law. So the third edition can be regarded as the last authentic edition. Subsequent editions by famous internationalists used the label and The Internationalist as a Scientist and Herald: Lassa Oppenheim 701 made this book ‘probably the most influential English textbook of international law’.2 The original book reveals only small traces of a national standpoint. Its success is rather due, as will be suggested here, to a clear systematic approach underlying Oppenheim’s legal theory. Although the theory is hardly presented in the book, it is the reason for its clarity and popularity. 2 Methodology As has long been noted, Oppenheim’s German training is very conspicuous in the writing of his International Law. But ‘positivism’ is a label which combines quite a variety of approaches. Most of them have not been very well investigated, with the result that ‘positivism’ remains a vague and untrustworthy tag. Moreover, it is very difficult to explain Oppenheim’s methodology as he wrote so little about it. There is very little on his methodology to be found in his International Law. Personal views he reserved for articles and his lectures. Methodologies are so abstract that it might be useful and illustrative to present an instance of his argumentation as a clue to his systematic approach. Our example is taken from a lecture, a context in which Oppenheim tended to argue more freely and with less caution. In his International Law, however, he tackled problems in the same way. In the lecture he investigated the reasons why treaties have a binding force.3 Some of the more modern writers (Hall, Jellinek, Nippold) find the binding force of treaties in the self-restraint exercised by states in becoming a party to a treaty; others (Triepel) assert that it is the contracting states’ own will which gives binding force to their treaties; and, lastly, there is Bluntschli and his adherents who teach that the binding force of international treaties is to be found in the idea of right innate in mankind (im Rechtsbewusstsein der Menschheit). I believe that all these answers are unsatisfactory. I believe that the question as to the binding force of international treaties can be satisfactorily dealt with only by dividing it into several different questions and by answering those questions seriatim. First, the question to be answered is why are treaties legally binding? The answer must categorically be that this is so because there exists a customary rule of international law that treaties are binding. Secondly, the question might be put as to the origin of the existence of such customary rule. The answer must be that such rule is the product of several joint causes. Religious and moral reasons require such a rule quite as much as the interests of states, for no law could exist between nations if such rule did not exist. All causes which have been and are still working to create and maintain an international law underlie this question. And, thirdly, one might pose the question of how it is possible to speak of a legally binding force in treaties without a judicial authority to enforce their provisions. The answer must be that the binding force of treaties, although it is a legal force, is not the same as the binding force of contracts according to municipal law, since international law is a weaker law, and for this reason less enforceable than municipal law. But just as international law does not lack legal character in consequence of the fact that there is no central authority above the state which 2 Wight, ‘The Balance of Power’, in H. Butterfield and M. Wight (eds), Diplomatic Investigations (1966) 149, at 172. 3 L. Oppenheim, Lectures on Diplomacy as Part of International Law (unpublished manuscript: Trinity College, Wren Library, Add ms a 338 1/1 to 1/21, here 1/16 to 15 s). 702 EJIL 11 (2000), 699–712 could enforce it, so international treaties are not deficient of a legally binding force because there is no judicial authority for the enforcement of their provisions. Oppenheim starts by giving a brief overview of the previous solutions to the question together with some short critical remarks. It is also notable that he names many authors from various national backgrounds. He then puts the question with more precision. The remarkable feature of this reasoning is his division of problems.