FORUM PRESENTATION THE UNIDROIT PRINCIPLES OF INTERNATIONAL COMMERCIAL CONTRACTS AS AN EXAMPLE OF NON-STATE RULES OF LAW: A RIVAL OR A FRIEND OF POSITIVE LAW? <...> By Alberto Mazzoni (Italy) Author President of the International Institute for the Unifi cation of Private Law (UNIDROIT) Abstract The paper initially criticizes the ideological postulate, stemming from the legal nationalism and the legal positivism of the XIX and XX century, according to which law is either State law or international law applicable to States. <...> The paper focuses on one of these tensions in particular, namely the tension between State law, envisaged as the sole positive law, and non-State rules of law that are rules factually observed as law in www.kulawr.ru Volume 2 October 2015 Issue 2(4) Alberto Mazzoni The Unidroit Principles of International Commercial Contracts as an Example of Non-State Rules of Law. 271 action but do not belong to any national system of State law. <...> As an outstanding example of non-State rules of law, the paper argues that the UNIDROIT Principles of International Commercial Contracts (UPICC) present striking similarities with the lex mercatoria of the Middle Age, both in terms of the underlying goal (facilitating cross-border trade) and in terms of the method of formation (in the absence of converging national rules, the applicable better rule is sought at the higher level of a superior law based on reason). <...> Similarly, in today’s world judges and arbitrators may be inspired by UPICC in interpreting or supplementing the applicable national law, even in the absence of an express reference to such Principles by the parties. <...> Conclusively, UPICC as non-State rules of law may operate more as a friend than as a rival of positive State law. <...> Keywords Law, state, positive law, non-State rules of law, lex mercatoria, UNIDROIT Principles of International Commercial Contracts (UPICC), Roman law, ratio scripta DOI: 10.17803/2313-5395.2015.2.4.270-277 TABLE OF CONTENTS I. The tension between positive law and natural law .271 II. <...> The tension between State law and non-State rules of law.273 III. <...> Positive law: prospects for the future .277 I. THE TENSION BETWEEN POSITIVE LAW AND NATURAL LAW The nineteenth century saw the triumph of legal nationalism, followed by positivism and the strictly linked ideological postulate that law is not even conceivable unless it is envisaged <...>