Already in 1889, in the case of Lamu Island, the arbitrator Baron Lambermont indicated that oral agreements were considered odd because they did not reflect international usage. See Baron Lambermont`s arbitration award in the dispute lamu (1890) 22 Review of International Law and Comparative Legislation 349-360. Harvard Research, for example, has been very concerned about oral agreements. See the codification of 1935 contract law by Harvard Law School, draft convention on treaty law (1935) 29 AJIL supp 691 (“Without the instrument, there is no evidence of agreement, there is nothing to interpret or apply; In short, there is no contract other than the instrument that defines its provisions.” This has already been deplored by C Rousseau, General Principles of International Public Law, Volume 1 (Pedone 1944) 143. During the debates of the Commission on International Law, several members argued in favour of the idea that there could be no binding agreement without an instrument. See ILC, `Summary Records of the Second Session` (June 5 – July 29, 1950) YB ILC 1950, Volume 1, UN Doc A/CN.4/SER. A/1950, 64 and following. See also the observations of P Reuter, Introduction to the Law of treaties (3rd edn, University Press of France 1995) 27. Initially, international law did not accept any contractual reservations and rejected them, unless all parties accepted the same reservations. However, in order to encourage as many states as possible to join the treaties, a more straightforward reserve rule has been established. While some treaties still explicitly prohibit any reservations, they are now generally accepted to the extent that they are not incompatible with the objectives and objectives of the treaty. 78 The theoretically opposite term is the notion of “ius dispositivum,” that is, the right available to states, which can be modified as they see fit. B, for example, treaties entered into to deviate from the rules of international customary law or reservations about the provisions of the treaty involve the underlying ius dispositivum.
The concept of ius cogens must also be distinguished from that of erga omnes obligations, not least because certain norms of international law are proposed, which fall into both categories.