68. It is indispensably requisite that this science should be positive in character. What natural law and natural law methods have done for the law of nations in the past stands high above all doubt, but they have lost their value and importance for present and future times. Now and onwards the task is, in the first place, to ascertain and to give precision to the rules which have grown up in custom, and in the second place to formulate the enacted rules in their full content and in their full bearing. In doing so it will come to light that there are many gaps not yet regulated by law. Many of these gaps may be successfully filled up by a discreet employment of analogy, but many others will remain which can only be remedied by international legislation or by the development of customary law in the practice of the courts or otherwise. What science can do here is to make proposals _de lege ferenda_ of a politico-jural character, but it cannot and may not fill up the gaps. Science may also test and criticize, from the politico-jural standpoint, the existing rules of customary or enacted law, but, on the other hand, it may not contest their operation and applicability, even if convinced of their worthlessness. It must not be said that these are obvious matters and therefore do not need special emphasis. There are many recognized rules of customary law the operativeness of which is challenged by this or that writer because they offend his sense of what is right and proper. As an example thereof let us take the refusal by some well-reputed writers to include annexation after effective conquest (_debellatio_) among the modes, known to international law, of acquisition of state territory. They teach that _debellatio_ has no consequences in point of law, but only in point of fact; that it rests on naked might and brings the annexed area under the power of the victor only in point of fact and not in point of law. Here they are putting their politico-jural convictions in the place of a generally recognized rule of law. [Sidenote: The science of international law must be impartial.]