L’interpretazione dei trattati attraverso la pratical contruction

The interpretation rules of the Vienna Convention on the Law of Treaties (articles 31-33) which reflect customary international law, by the way aim at ensuring legal certainty. This, first of all, makes that treaties shall be interpreted in good faith. In this case, good faith might also be expressed in more specialized terms which are congenial to the realm of nemo potest venire contra factum proprium whenever a State party, by his subsequent practice in the application of the treaty, induce another to believe in the validity of a certain interpretation. Understood thus, the assessment of the subsequent practice as mean of interpretation , sometimes called “practical construction”, may be deduced from the international case-law. International tribunals applies this rule as supplementary means of interpretation, by virtue of Article 32 of the Vienna Convention, in order to correct an unsatisfactory interpretation or to confirm an otherwise achieved interpretation. Practical construction must be clearly distinguished from any subsequent practice in the application of the treaty which establishes the agreement of the parties regarding its interpretation. This last hypothesis - only apparently similar to practical construction and expressly regulated by Article 31, para. 3. (b) of the Vienna Convention - looms a real “authentic interpretation” resulting from a subsequent tacit agreement. This agreement requires a common understanding regarding the interpretation of the treaty which all parties have to be aware and accept. Conversely, practical construction does not require that the practice must be performer by all the contracting parties and the practice of an individual party - or of only some parties - becomes an useful element of interpretation. The practical construction ultimately, doesn’t provide the existence of any consent: so the practice of an individual State also may be taken into account. Ultimately, it is possible to construe the practical construction as resting upon a (sort of) responsibility incurred by the agens State for having created - by his subsequent practice in the application of the treaty - an appearance of fact.