as those requirements are understood at the day. Thus an alleged rule of International Law must satisfy two conditions in order to maintain its validity. It must be the product of the actual or the tacit consent of States; that is, it must have been generally agreed to by treaty, or constantly observed in practice; and it must be in harmony with a scheme of International Morality, which is variously styled the Law of Nature, the Law of God, Abstract Justice, the Law of Right, Reason, and the like.
When it is remembered how comparatively rare, in past times, Difficulty of forming distinct rules — have been the points of contact of Eastern States otherwise than by War, in what a desultory way the intercourse between the States has been conducted, how fragmentary and imperfect is the evidence of that intercourse, and yet how indefinitely extended in some directions is the field from which the International Lawyer has to glean his proofs of usage and consent, it does not seem surprising that the whole region of International Law should be one of uncertainty and conjecture. But when to this are added the intricacy and depth of any problem which depends for its solution upon a true and exact view of Abstract Morality as binding on States, and the difficulties inherent in the interpretation of the documentary conventions which are alleged to afford evidence of consent, the uncertainty attaching to the most elementary rule of International Law begins to rise to a very high pitch. This sort of Law shares all the notorious uncertainty which cleaves to rules of national law, besides possessing a special uncertainty of its own, through the absence of express legislation, the paucity of the instances on which conclusions or analogies can be based, and the variety of the national languages, manners, and proclivities amidst which the Law has grown up.
International Law is, however, not merely infected with an inherent uncertainty as to the purport and form of its general rules, but, when a rule is clearly ascertained, there are special
