All that the word "compulsory" in this connection means is "agreed to in advance." The general provisions of the Court {21} Statute[2] describe the jurisdiction of the Court as extending to any case which the Parties, either after it has arisen or by "treaties and conventions in force,"[3] choose to submit. The so-called optional clause relating to the so-called compulsory jurisdiction in effect provides that as to certain defined classes of cases the parties agree, now, in advance of any dispute, that disputes of those particular characters will be submitted to the Court. The definition of these classes of disputes is found in Article 36 of the Statute of the Court, and in this regard follows generally in its language the provisions of the second paragraph of Article 13 of the Covenant, which declares that these particular classes of disputes are "among those which are generally suitable for submission to arbitration or judicial settlement." By the so-called optional clause relating to the Court Statute, it is these classes of disputes as to any or all of which the jurisdiction of the Court may be accepted as "compulsory _ipso facto_ and without special agreement, in relation to any other Member or State accepting the same obligation." 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 {22} 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.