History of Public International Law - Hugo Grotius

Hugo Grotius

International practices, customs, rules and treaties proliferated to the point of complexity. Several scholars sought to compile them all into organized treatises. The most important of these was Hugo Grotius, whose treatise De Jure Belli Ac Pacis Libri Tres is considered the starting point for modern international law. Before Hugo Grotius, most European thinkers treated law as something independent of mankind, with its own existence. Some laws were invented by men, but ultimately they reflected the essential natural law. Grotius was no different, except in one important respect: Unlike the earlier thinkers, who believed that the natural law was imposed by a deity, Grotius believed that the natural law came from an essential universal reason, common to all men.

This rationalist perspective enabled Grotius to posit several rational principles underlying law. Law was not imposed from above, but rather derived from principles. Foundation principles included the axioms that promises must be kept, and that harming another requires restitution. These two principles have served as the basis for much of subsequent international law. Apart from natural-law principles, Grotius also dealt with international custom, or voluntary law. Grotius emphasized the importance of actual practices, customs and treaties—what "is" done—as opposed to normative rules of what "ought to be" done. This positivist approach to international law strengthened over time. As nations became the predominant form of state in Europe, and their man-made laws became more important than religious doctrines and philosophies, the law of what "is" similarly became more important than the law of what "ought to be."