A: Extended Abstract

1. Introduction

Article 31(3)(b) of the VCLT 1969 Vienna Convention on the Law of Treaties (VCLT) requires that, in the process of treaty interpretation, “any subsequent practice in the application of the treaty which establishes the agreement of the parties regarding its interpretation” shall be taken into account, in addition to the other elements of the general rule of interpretation. A similar rule exists in the Vienna Convention on the Law of Treaties between States and International Organizations, or between International Organizations (VCLT II). The International Court of Justice has repeatedly emphasized in its jurisprudence the customary nature of the general rule of interpretation, including the impact of subsequent practice on treaty interpretation. A comparable approach can be found in arbitral awards, the WTO Appellate Body, human rights treaty bodies, and domestic courts. To determine the precise scope of the rights and obligations provided for in a treaty, it is essential, alongside the context and other elements of the general rule of interpretation, to consider the practice and attitude of the parties in application the treaty. It is reasonable to believe in the "living and dynamic intention of the parties". Such intention manifests itself over time through the conduct and attitude of the parties—a reality that can be referred to as "interpretation through practice".

2. Research Gap and Objective

Despite treaty and customary foundations, and its widespread reflection in judicial practice, there is no precise definition of the structure and form of subsequent practice in treaty interpretation. The primary question of this study concerns the constitutive elements, and forms of subsequent interpretative practice. The present study forgoes an examination of the impact of subsequent practice on the content of the treaty—a phenomenon that may manifest as substantive expansion, contraction, or clarification of the treaty’s provisions.

3. Methodology

The method of study in this paper is descriptive-analytical. this research has a theoretical approach, and aim is to explain the Structure and Form of subsequent practice. Although this aspect is not explicitly reflected in the title of the study, a significant part of our analysis is devoted to examining the issue in light of the judgments of the International Court of Justice.

4. Key Findings

The research findings indicate that although a clear distinction between the forms of subsequent practice is not explicitly evident in Articles 31 and 32 of both VCLT I and VCLT II, two types of subsequent practice can be identified, which respectively have conclusive and supplementary effects in treaty interpretation. These findings can be reinforced in the light of the travaux preparatoires of the VCLT I and VCLT II, reports of the International Law Commission, judicial practice of both international and domestic courts and tribunals, as well as the teachings of the most highly qualified publicists.

5. Conclusion

Consensual subsequent practice, TANTAMOUNT to a complete customary rule, constitutes a clear, consistent, uniform, and generally accepted sequence of acts, statements, or attitudes by the parties in the implementation of a treaty and must be taken into account in treaty interpretation. In this context, we observe a form of subsequent practice that reflects the agreement or, at a minimum, the absence of effective objection by the majority of the treaty parties. It is not necessary to demonstrate the participation of every party in the formation or development of the practice; however, general practice and a shared understanding regarding the interpretation of the treaty suffice. Such subsequent practice, tantamount to a customary rule, embodies a sequence of conduct and attitudes, as well as the overall agreement of the parties, and should be taken into account in the interpretation of the treaty. The general rule of interpretation, as outlined in Articles 31 and 32 of both the VCLT I and VCLT II and recognized as customary rule international law, affirms this necessity. Legal precedents, findings of the International Law Commission (ILC), and legal doctrine all establish that the consensual subsequent practice of the parties to a treaty, when considered alongside other elements under the general rule of interpretation, constitutes an authentic element in interpreting all types of treaties. The absence or deficiency of any aforementioned characteristics results in non-consensual subsequent practice, reducing subsequent practice to a merely supplementary means of treaty interpretation. This article employs a descriptive-analytical method to examine legal doctrine, international documents, and international judicial precedents, aiming to explore the role of subsequent practice in treaty interpretation. The present study forgoes an examination of the impact of subsequent practice on the content of the treaty—a phenomenon that may manifest as substantive expansion, contraction, or clarification of the treaty’s provisions.

The absence or deficiency of any aforementioned characteristics results in non-consensual subsequent practice, reducing subsequent practice to a merely supplementary means of treaty interpretation. This article employs a descriptive-analytical method to examine legal doctrine, international documents, and international judicial precedents, aiming to explore the role of subsequent practice in treaty interpretation. The present study forgoes an examination of the impact of subsequent practice on the content of the treaty—a phenomenon that may manifest as substantive expansion, contraction, or clarification of the treaty’s provisions.