The classes of "legal disputes" mentioned in Article 36 of the Court Statute are as follows:
"legal disputes concerning:
(a) The interpretation of a treaty;
(b) Any question of international law;
(c) The existence of any fact which, if established, would constitute a breach of an international obligation;
(d) The nature or extent of the reparation to be made for the breach of an international obligation."
In regard to these definitions of classes of disputes, it is necessary to make some general observations. No matter what definition may be made in advance as to the classes of disputes which are to be submitted to the Court, a difference of opinion may exist in any given case as to whether the particular dispute which has arisen is or is not within one of the defined classes.
It follows that the mere definition of classes of disputes which, by agreement in advance, are to be submitted to a particular tribunal, is not in itself sufficient; any such definition must be accompanied by a provision for a case when one of the parties to a dispute claims that the particular dispute is within the defined class and the other party to the dispute does not admit that the dispute is within the defined class; some method must be provided for determining that preliminary question of jurisdiction.
Let me put this concretely: let me suppose that two Members of the League have agreed to the optional clause and that a dispute arises between them. One party to the dispute says that the question involved concerns the interpretation of a treaty and accordingly submits the question to the Permanent Court of International Justice in accordance with the procedure under the Statute of that Court. The other party to the dispute says that the dispute does not in any way concern the interpretation of the treaty and submits the matter to the Council of the League under Article 15 of the Covenant.
Clearly there would be here for decision a preliminary point of jurisdiction and, in so far as the optional clause is concerned, the matter is covered by the Statute of the Court in the final paragraph of Article 36, reading as follows: