The importance of a scholar like Hugo de Groot can be viewed in different ways. A systematic analysis of his works would clarify the coherence and depth, an historical approach would do the same for his sources and the extent of his originality. Other possibilities would be to trace the further development of his (legal and political) thinking or to ask what inspiration his works can still give towards the solution of problems today. Another approach has been adopted in the present contribution, viz., a discussion of Grotius' influence on a particular thinker of a later period, the Neapolitan lawyer and philosopher Giambattista Vico(1668–1744). Two aspects of his influence will be considered. In the first place, the question why Vico himself attributed such particular importance to Grotius. Vico even named Grotius as one of his “authors”. Vico employs the term “author” as a title of honour for his mentors in literature whom he considers especially important and in whose work he recognizes aspects of his pwn thinking which are of exceptional importance. However, Vico's attitude to Grotius does not consist solely of grateful admiration. In his principal work, the New Science, of which the first edition was published in 1725, and the last, totally rewritten, posthumous edition appeared in 1744, Vico's recognition of Grotius' merits is certainly still apparent, although his criticism has, by this stage, taken a dominant role. Vico's opposition to the predominant Cartesian rationalism, which he had already expressed in his De nostri temporis studiorum ratione of 1709 and in his De antiquissima italorum sapientia ex linguae latinae originibus eruenda, liber primus sive metaphysicus of 1710, also extends to the rationalist school of natural law of which he considers Grotius, Selden and Pufendorf to be the main representatives.

In George H. Sabine's great work, A History of Political Thought, he makes the following overall judgment on Grotius’ writing:

“Grotius' importance in the history of jurisprudence rests not upon a theory of the state or upon anything that he had to say about constitutional law, but upon his conception of a law regulating the relations between the sovereign states.”

Grotius may be considered as the founder of the modern theory of international law and of the modern humanist theory of natural law. His famous work De hire belli ac pads libri tres, first published in 1625, combined an elaboration of his contributions, which formed the foundation to both these theories.

It may not seem a very ambitious project to show which sources Grotius used in his two systematic expositions of International Law, De jure praedae and De jure belli ac pacis. One could simply refer to the indices of authors cited by Grotius in the English translations of the “Classics of International Law” series and analyse these impressive lists, looking, inter alia, for significant differences between them. However, such an approach, though no doubt useful, is only a very partial answer to the question of the “sources”, or perhaps even the “foundations”, of the Grotian system. I would suggest that it could even be seriously misleading. First of all, we have to assess Grotius' academic tools, with their mixture of references to the Scriptures, the patres ecclesiae and classical poets and philosophers in preference to sixteenth and seventeenth century authors. What is their function? As our interest is in international law, and not in philology or theology, we may well wonder how we are to deal with this mass of materials, most of which seems at first sight quite irrelevant to our subject. The abundance of wide ranging quotations in De jure belli ac pacis led Voltaire to accuse Grotius of pedantry, a charge that was also made against him as a politician and a diplomat by his contemporaries as well as by historians. If we do not consider this sufficient reason for disregarding, inter alia Plautus, Ovid, St. Ambrose and St. Augustine as “ornamental” rather than “structural” elements in the Grotian system, we may be encouraged by the example of as ardent an admirer of Grotius as Telders. His severe pruning of the overburdened text of De jure belli ac pacis was meant to reintroduce the book into general use as “the first treatise on international law ever written that aimed at completeness”.6

In 1918, just before the end of the First World War, a booklet of barely ninety pages was published in the Hague under the title “De Drie Treden van het Volkenrecht” (in English “The Three Stages in the Evolution of the Law of Nations”). For a work dealing with a subject relating to international law, it was an incredible success: it was twice reprinted in its Dutch version and was translated into French, German and English. The key to its success may well have been its simple plot: as in a Punch and Judy show, the cast had but two main characters – the good boy and the bad boy. The hero was Hugo Grotius, whose 400th birthday we are commemorating this year; the villain was Eméric de Vattel, a man who wrote a book in 1758 in which, according to the author of “The Three Stages”, he gave a Judas kiss to the hero precisely at the moment that he might have become victorious. The author leaves us in no doubt where his sympathies lie; the lines in which he characterizes the qualities of his two leading characters by comparing their Christian names have become quite famous: “the Dutchman is called Hugh (Huig in Dutch), a bluff and sturdy name; the other is called Emeric: the name of a balletmaster‥”.

1983 sees the 400th anniversary of Grotius' birth. This is an appropriate time to consider what the Netherlands has made of – and is still making of – the enormous heritage of this great Dutchman.