The Significance of Subsequent Agreements and Practice of the 1969 Vienna Convention on the Law of Treaties in the Development of International Law: The Analysis of the Notable Navigational and Related Rights and Whaling Decisions

The Vienna Convention on the Law of Treaties has been applied by international legal scholars, international courts and tribunals, and states since 1969, especially an application of treaty interpretation under Article 31 to 33 of the Convention. The current trend aims at applying subsequent agreements and subsequent practice in interpretation proceedings. However, this might lead to a broad interpretation, resulting in the inconsistency of parties’ intention. Thus, there should be a scope or guideline for international courts and tribunals to apply and limit the treaty interpretation. This essay focuses on a better understanding of how international courts and tribunals use subsequent agreements and practice in their cases, studying and comparing the notable Navigational and Related Rights and Whaling decisions from the International Court of Justice to analyse the legal status of judicial views applied in subsequent agreements and in subsequent practice. The essay also explores how far the interpretation of courts and tribunals can be extended by focusing on the intentions of the parties and the object and purpose, the principle of restrictiveness and intertemporal law. Keywords: treaty interpretation, subsequent agreements, subsequent practice, 1969 Vienna Convention on the Law of Treatie