1The law common to nations present within the Roman empire, the jus gentium had as its vocation to extend to all of them and to represent, alongside the natural law common to animate beings, the particular one of humankind. Grotius reserves natural law to men: jus gentium becomes the law that independent peoples (the empire no longer existing) institute to complement the regulation of natural laws. While accepting this point of departure (a plurality of independent states), the other moderns were to refuse (Hobbes, Pufendorf) or admit (Locke) the existence of a law instituted by mutual consent and not the decision of a sovereign. Montesquieu is on Grotius’s side: the law of nations is part of the positive laws, it is non-natural, established, with no need of a sovereign to institute it (EL, I, 3). Yet Grotius’s point of view undergoes three inflections:
1. The natural laws are discovered through the hypothesis, absent in Grotius, of a state of nature anterior to the establishment of societies: common to animals, instinctive and affective, they go beyond the rules taught late by reason (duties toward God, the mutual necessity of relations with others), at the end of a process in which the faculty of knowing is activated and the social bond takes a human form.
2. Montesquieu uses freely the Hobbesian notion of state of war: following on the institution of societies, non-natural (EL, I, 3), it causes the positive laws to be established (law of nations, political or civil law, according to whether it concerns the settling of relations between nations, between the government and the governed, or between all citizens). Between nations, the relation to war is never eliminated: the things concerned “are of a nature not to be able to be settled without force or a suspension of force” (“sont de nature à ne pouvoir être réglées que par une force ou par une suspension de force”, Pensées, no. 1814). The law of nations settles the offensive force of each state (EL, X, 1). In the mutual relations, princes “are governed by force; they can continually force and be forced. Whence it follows that the treaties they have made by force are as obligatory as those which they would have made voluntarily” (EL, XXVI, 20). If treaties suspend only the use of force and are valid even when they are made under constraint, there is, as in Hobbes, a state of war between states, settled and not suppressed by the law of nations, with however this capital difference: to be governed by force and what settles it (the law of nations) is to be deprived of the freedom that consists of being governed by civil laws. The law of nations is thus not civil law. It is however “a civil law, not in truth that of a particular country, but of the World” (LP, [‣]), or yet again “the civil law of the universe” (EL, XXVI, 1). This is to play loosely with a Stoic formula: it is each people and not, in the Stoic manner, each man, who is a citizen of the universe. The law of nations is public, it connects governments and not individuals, it supposes the plurality of peoples which the size of the planet makes necessary. To refer to civil law is to refuse to let the law of nations be foreign to the natural justice that founds the civil law among individuals. To mark the limits of this comparison (peoples have neither a common government nor common civil laws), Montesquieu defined Jus gentium as “the political law of nations”: the veritable law of nations sometimes authorizes preventive attack, each time a state is too weak to exert otherwise its right to natural defense, whereas an individual must abstain from it because he lives under the protection of civil law (EL, X, 1 et 2).
3. For Grotius, all instituted law is voluntary and thus measured by will. It is the usages to which peoples have in fact consented that legitimize rules often more permissive than what natural defense would authorize, for example the right to exterminate and enslave the women and children of the state against which one has waged a declared war. Montesquieu dispenses with this reference to will: the law of nations is established without resulting from a contract; like any human law, it is related to material (climate, terrain, mode of subsistence), religious and political conditions; finally the established fact (a specific right of peoples, proper to the Iroquois, the Romans, the Franks or the Tartars) never makes the veritable law, the law of nations “based on the true principles” (EL, I, 3), that which goes no farther than what is necessary for natural defense (EL, X, 2, 3), and the exact practice of which presupposes political (moderation), religious (a gentle religion) and economic (the progress of trade) conditions.
Mark H. Waddicor, Montesquieu and the Philosophy of Natural Law, La Haye (The Hague): Martinus Nijhoff, 1970.
Marc Belissa, “Montesquieu, L’Esprit des lois et le droit des gens”, in Le Temps de Montesquieu, Michel Porret et Catherine Volpilhac-Auger ed., Geneva: Droz, 2002, p. 171-185.
Jean Terrel, “À propos de la conquête : droit et politique chez Montesquieu”, Revue Montesquieu 8 (2006), http://montesquieu.ens-lyon.fr/spip.php?article330.
Jean Terrel, “Sur le livre X de L’Esprit des lois : le problème de la conquête”, (Re)Lire L’Esprit des lois, Luigi Delia et Catherine Volpilhac-Auger ed., Publications de la Sorbonne, 2014, p. 107-122.