[Sidenote: Treaties as Source of International Law.]
§ 18. Treaties are the second source of International Law, and a source which has of late become of the greatest importance. As treaties may be concluded for innumerable purposes,[14] it is necessary to emphasise that such treaties only are a source of International Law as either stipulate new rules for future international conduct or confirm, define, or abolish existing customary or conventional rules. Such treaties must be called _law-making treaties_. Since the Family of Nations is not a State-like community, there is no central authority which could make law for it in a similar way as Parliaments make law by statutes within the States. The only way in which International Law can be made by a deliberate act, in contradistinction to custom, is that the members of the Family of Nations conclude treaties in which certain rules for their future conduct are stipulated. Of course, such law-making treaties create law for the contracting parties solely. Their law is _universal_ International Law then only, when all the members of the Family of Nations are parties to them. Many law-making treaties are concluded by a few States only, so that the law which they create is _particular_ International Law. On the other hand, there have been many law-making treaties concluded which contain _general_ International Law, because the majority of States, including leading Powers, are parties to them. General International Law has a tendency to become universal because such States as hitherto did not consent to it will in future either expressly give their consent or recognise the respective rules tacitly through custom.[15] But it must be emphasised that, whereas custom is the original source of International Law, treaties are a source the power of which derives from custom. For the fact that treaties can stipulate rules of international conduct at all is based on the customary rule of the Law of Nations, that treaties are binding upon the contracting parties.[16]
[Footnote 15: Law-making treaties of world-wide importance are enumerated below, §§ 556-568b.]
[Sidenote: Factors influencing the Growth of International Law.]
§ 19. Thus custom and treaties are the two exclusive sources of the Law of Nations. When writers on International Law frequently enumerate other sources besides custom and treaties, they confound the term "source" with that of "cause" by calling sources of International Law such factors as influence the gradual growth of new rules of International Law without, however, being the historical facts from which these rules receive their legal force. Important factors of this kind are: Opinions of famous writers[17] on International Law, decisions of prize courts, arbitral awards,[18] instructions issued by the different States for the guidance of their diplomatic and other organs, State Papers concerning foreign politics, certain Municipal Laws, decisions of Municipal Courts.[19] All these and other factors may influence the growth of International Law either by creating usages which gradually turn into custom, or by inducing the members of the Family of Nations to conclude such treaties as stipulate legal rules for future international conduct.