2.1. Application of the Vienna Convention to the interpretation of the EPC

The European Patent Organisation is not a party to the Vienna Convention. Moreover, as the Enlarged Board observed in G 5/83, the provisions of the Vienna Convention do not apply to the EPC ex lege, since it applies only to treaties which are concluded by States after the entry into force of the Vienna Convention with regard to such States (Art. 4 Vienna Convention). At the time of conclusion of the EPC, the Vienna Convention was not in force. Nevertheless, there were convincing precedents for applying the rules for interpretation of treaties incorporated in the Vienna Convention to a treaty to which they do not directly apply (see also G 2/12 and G 2/13, point 4 of the Reasons). The International Court of Justice had already applied principles expressed in the Vienna Convention to situations to which the Convention strictly did not apply, whilst the ECtHR, the Federal German Constitutional Court and the House of Lords (England) had also applied the principles of interpretation in Art. 31 and 32 Vienna Convention to treaties to which strictly they do not apply. After a careful study of the whole subject, the Enlarged Board concluded that the EPO had to do the same.

In J 8/82 (OJ 1984, 155) the Legal Board noted that it was well recognised that Art. 31 and 32 Vienna Convention merely codified existing public international law. In J 10/98 (OJ 2003, 184) the Legal Board stated that, although the Vienna Convention did not expressly apply to the interpretation of the EPC, PCT or the Paris Convention, since it came into force at a later date than all of those treaties, in accordance with what had been recognised by the Enlarged Board in G 5/83, its principles of interpretation were a valuable guide to the interpretation of all treaties executed both before and after it. In T 1173/97 (OJ 1999, 609) the board stated that although the Vienna Convention was not applicable to the EPC, it had considerable authority and had frequently been cited by the boards of appeal when applying principles laid down in it. See also J 7/21 and T 695/18.