The article concerns the obligations to negotiate and conclude agreements in good faith (pactum de negotiando and pactum de contrahendo), which are used in international legal practice to more efficiently settle disputes or negotiate new agreements in various areas of international law. These obligations, however, are sometimes mixed together and misunderstood. They also give rise to various interpretation disputes related to their existence as obligations and their content. The aim of the study is to show that these are not simple obligations, but bundles of obligations. Such perception of them makes it possible to distinguish both pacta and penetrate into their rich content, as well as to unequivocally apply to their performance the principle of performing international obligations in good faith (Art. 2(2) of the UN Charter), especially in the form of pacta sunt servanda (Art. 26 of the Vienna Convention on the Law of Treaties).

This article is an attempt to identify the essence of new positivism, described by Ludwik Ehrlich as a method of interpretation of international law. The evolution of his views on international law is examined with respect to the place of this method from the beginning of 1920s until his retirement in 1961. The article expounds on both the theoretical and methodological aspects of new positivism, according to which judicial decisions should be taken into account in addition to international treaties and customs for the determination of international law. The question of the obligatory force of international law is discussed as being related to the principle of good faith, which is at the core of Ehrlich’s views on international law. The article offers suggestions on how the method of new positivism might be used and what tasks it can fulfil today. It also makes an attempt to critically analyse Ehrlich’s method and to characterize it both in general and in the context of the theory of international law.