For its effects to be determined, the treaty must first be viewed in isolation, irrespective of any other legal rules which may be applicable in a given situation (without prejudice to problems of interpretation; see below, No. 145) first with regard to parties (Section I) and then to non-parties (Section II), whereupon it will be considered in relation to other rules which may have to combine with it, giving rise to some specific issues (Section III).(*)

I Effects with regard to the parties 137 It has been noted (see above, No. 50) that a treaty, by its very nature, closely links a juristic act and a rule laid down by means of that act. The effects of the treaty relate to the authors of the act: from their will do they proceed and they are nothing apart from that will. That very generally is the basic principle. It makes it possible to formulate from the outset a problem arising even before the treaty is being performed, namely how to determine the intention of the parties. This is the issue of treaty interpretation, which is the subject of Sub-Section 1. Apart from interpretation, several aspects regarding the scope and extent of the undertaking concern the 'application' of a treaty. The application of treaties in the municipal order has already been dealt with (see above, No. 44); their application in space and time remains to be considered in Sub-Section 2.(*)

1. Interpretation

138 States or international organizations which are parties to a treaty have to apply the treaty and therefore to interpret it. In the case of States, the organs having concluded the treaty are the most qualified to do so, but their courts also have to interpret an increasing number of treaties. If the parties to a treaty agree on a common interpretation either by a formal treaty or otherwise, this interpretation acquires an authentic character and prevails over any other. But other entities beside the parties also interpret the treaty, for instance an arbitral tribunal or an international organization which, although not a party, has to apply a treaty or control its application, in particular when the treaty concerned is its constituent charter.(*) 139 The fact that different entities are called upon to interpret the treaty does not in principle affect the manner in which interpretation must be performed. What does change from one situation to another is the extent of the interpreter's powers, and also the effects of his interpretation. While the right of the governments parties to interpret a treaty is unchallenged, the same cannot be said of municipal courts whose powers, laid down by their national Constitution, vary considerably from State to State and occasionally from court to court within the same country. In international organizations, it is generally accepted that each organ, within its functions, is called upon to interpret the treaties which concern it although the interpretations of some, especially judicial, organs may in some cases be binding on the other organs as well.