 Welcome back. In order to have a complete overview of the making of treaties, the last question to turn to is the issue of their validity. Of course, we shall also study how treaties are applied or they are interpreted and eventually suspended or terminated. But I leave those issues for a later week because they relate to the application of international law rather than to the making of international law, which is our topic for this week. Let me first introduce the concept, the notion of validity. One must remember that a treaty is a legal act. It is an instrument governed by international law which embodies the consent of the contracting parties to a certain obligations, those obligations being applicable to a certain object. In order to be binding under international law, the treaty must be valid. That is, it must comply with some essential requirements. And lacking those essential requirements, the instrument will simply not have entered within the realm of international law. So the issue of the validity of treaties is really to determine whether the instrument that looks like a treaty is somehow entitled to be part of international law and to carry with it the binding force of international law. If the treaty is invalid, the instrument will somehow be rejected out of the international legal order. It will be null and void. Of course, this would not make the instrument disappear from a material, a factual point of view, and the negotiations leading to it would simply remain historical events that have taken place. But as the instrument would not be considered as binding under international law, it would not be part of it, and it would remain outside of it. And lacking essential elements, the invalid treaty would have to be considered as not being part of international law from its infancy, from the very beginning. Invalidity is retroactive. The grounds for invalidating treaties are listed in the Vienna Convention. In Article 42 paragraph one of the Vienna Convention makes very clear that those grounds are in limited numbers. Only the grounds that are listed in the Convention can be invoked in order to impeach the validity of a treaty. And the reason for this is legal security, as it is not easy to conduct international negotiations leading to the conclusion of treaty. All those efforts should not be lightly put in danger of being set aside later if one of the contracting parties having certain thoughts about the treaty could too easily get rid of it by pretending that it is not valid. However, on the other hand, there is a need to protect the integrity of international law itself. It cannot be accepted that the force of the law be given to instruments which turn the law on its head. Instruments that indeed exist, but only because some essential rules have been ignored. And therefore, any theory about invalidity of legal acts is precisely about establishing that balance between legal security and the integrity of the legal order. The invalidity of a treaty as a legal instrument can stem from three main range of reasons. First, the treaty can be null and void because the contracting parties had no legal capacity to enter into it. Second, the treaty can be null and void because consent to it has not been properly given. Third, the treaty can be null and void because its very object is impermissible. Let me turn first to the issue of capacity. It can be easily dealt with. Article 6 of the Vienna Convention recalls a basic principle of international law which stems from the equal sovereignty of states. And I quote, every state possesses capacity to conclude treaties, end of quote. Hence, for states, the question of legal capacity is not an issue. All states have the same and full legal capacity to conclude treaties. For international organizations, the issue is a little bit more complicated. And as you may recall, international organizations are specialized legal entities and their legal capacity depends on the scope of their respective competences. Article 6 of the 1986 Vienna Convention simply refers to the rules of the organization. That is, most of the time, the treaty establishing the organization to determine the extent of the capacity of the organization to conclude treaties. So the capacity of international organizations to conclude treaties must be established on a case-by-case basis, taking into account the organization concerned, the object of the treaty it intends to conclude. Additionally, if the capacity of the organization to conclude treaties is not explicitly addressed by its rules, the implied powers doctrine, which has already been mentioned when talking about international organization, that doctrine may be used in order to consider that despite the silence of the treaty, the organization has some capacity to conclude treaties. The implied powers doctrine has notably been used by the European Court of Justice back in 1971 in the landmark case, the ERTA case, in order to justify the conclusion of treaties by the European economic community at the time, now the European Union. There is no need to go too much into details about that case. But what should, however, remember that the legal capacity of any international organization and the scope of such capacity should be appraised not only by looking at the written rules of the organization on the issue, but also by taking into account the implied powers doctrine? This is as far as the capacity of contract to contract treaties is concerned. In the next video, we'll explore the grounds for invalidity based on the effect of consent.