The Law of Nations or the Principles of Natural Law (1758)

Emmerich de Vattel

Of Faith Between Enemies: of Stratagems, Artifices in War, Spies, and Some Other Practices

§ 174. Faith to be sacred between enemies.
THE faith of promises and treaties is the basis of the peace of nations, as we have shown in an express chapter (Book II. Ch. XV.) It is sacred among men, and absolutely essential to their common safety. Are we then dispensed from it towards an enemy? To imagine that between two nations at war every duty ceases, every tie of humanity is broken, would be an error equally gross and destructive. Men, although reduced to the necessity of taking up arms for their own defense, and in support of their rights, do not therefore cease to be men. They are still subject to the same laws of nature: — otherwise there would be no laws of war. Even he who wages an unjust war against us is still a man: we still owe him whatever that quality requires of us. But a conflict arises between our duties towards ourselves, and those which connect us with other men. The light to security authorizes us to put in practice, against this unjust enemy, every thing necessary for repelling him, or bringing him to reason. But all those duties, the exercise of which is not necessarily suspended by this conflict, subsist in their full force: they are still obligatory on us, both with respect to the enemy and to all the rest of mankind. Now, the obligation of keeping faith is so far from ceasing in time of war by virtue of the preference which the duties towards ourselves are entitled to, that it then becomes more necessary than ever. There are a thousand occasion, even in the course of the war, when, in order to check its rage, and alleviate the calamities which follow in its train, the mutual interest and safety of both the contending parties requires that they should agree on certain points. What would become of prisoners of war, capitulating garrisons, and towns that surrender, if the word of an enemy were not to be relied on? War would degenerate into an unbridled and cruel licentiousness: its evils would be restrained by no bounds; and how could we ever bring it to a conclusion and re-establish peace? If faith be banished from among enemies, a war can never be terminated with any degree of safety, otherwise than by the total destruction of one of the parties. The slightest difference, the least quarrel, would produce a war similar to that of Hannibal against the Romans, in which the parties fought, not for this or that province, not for sovereignty or for glory, but for the very existence of their respective nations.1 Thus it is certain that the faith of promises and treaties is to be held sacred in war as well as in peace, between enemies as well as between friends.2

§ 175. What treaties are to be observed between enemies.
The conventions, the treaties made with a nation, are broken or annulled by a war arising between the contracting parties, either because those compacts are grounded on a tacit supposition of the continuance of peace, or because each of the parties, being authorized to deprive his enemy of what belongs to him, takes from him those rights which he had conferred on him by treaty. Yet here we must except those treaties by which certain things are stipulated in case of a rupture, — as, for instance, the length of time to be allowed on each side for the subjects of the other nation to quit the country, — the neutrality of a town or province, insured by mutual consent, etc. Since, by treaties of this nature, we mean to provide for what shall be observed in case of a rupture, we renounce the right of cancelling them by a declaration of war.

For the same reason, all promises made to an enemy in the course of a war are obligatory. For when once we treat with him whilst the sword is unsheathed, we tacitly but necessarily renounce all power of breaking the compact by way of compensation or on account of the war, as we cancel antecedent treaties, otherwise it would be doing nothing, and there would be an absurdity in treating with the enemy at all.

§ 176. On what occasions they may be broken.
But conventions made during a war are like all other compacts and treaties, of which the reciprocal observance is a tacit condition (Book II. § 202): we are no longer bound to observe them towards an enemy who has himself been the first to violate them. And even where this is a question of two separate conventions which are wholly unconnected with each other, — although we are never justifiable in using perfidy on the plea of our having to do with an enemy who has broken his word on a former occasion, we may nevertheless suspend the effect of a promise in order to compel him to repair his breach of faith; and what we have promised him may be detained by way of security, till he has given satisfaction for his perfidy. Thus, at the taking of Namur, in 1695, the King of England caused Marshal Boufflers to be put under arrest, and, notwithstanding the capitulation, detained him prisoner, for the purpose of obliging France to make reparation for the infractions of the capitulations of Dixmude and Deinse.3

§ 177. Of lies.
Good-faith consists not only in the observance of our promises, but also in not deceiving on such occasions as lay us under any sort of obligation to speak the truth. From this subject arises a question which has been warmly debated in former days, and which appeared not a little intricate at a time when people did not entertain just or accurate ideas respecting the nature of a lie. Several writers, and especially divines, have made truth a kind of deity, to which, for its own sake, and independently of its consequences, we owe a certain inviolable respect. They have absolutely condemned every speech that is contrary to the speaker’s thoughts: they have pronounced it to be our duty, on every occasion when we cannot be silent, to speak the truth according to the best of our knowledge, and to sacrifice to their divinity our dearest interests rather than be deficient in respect to her. But philoterests, of more accurate ideas and more profound penetration have cleared up that notion, so confused, and so false in its consequences. They have acknowledged that truth in general is to be respected, as being the soul of human society, the basis of all confidence in the mutual intercourse of men, — and, consequently, that a man ought not to speak an untruth, even in matters of indifference, lest he weaken the respect due to truth in general, and injure himself by rendering his veracity questionable even when he speaks seriously. But in thus grounding the respect due to truth on its effects, they took the right road, and soon found it easy to distinguish between the occasions when we are obliged to speak the truth, or declare our thoughts, and those when there exists no such obligation. The appellation of lies is given only to the words of a man who speaks contrary to his thoughts, on occasions when he is under an obligation to speak the truth. Another name (in Latin, falsiloquium4) is applied to any false discourse to persons who have no right to insist on our telling them the truth in the particular case in question.

These principles being laid down, it is not difficult to ascertain the lawful use of truth or falsehood towards an enemy on particular occasions. Whenever we have expressly or tacitly engaged to speak truth, we are indispensably obliged to it by that faith of which we have proved the inviolability. Such is the case of conventions and treaties: — it is indispensably necessary that they should imply a tacit engagement to speak the truth; for it would be absurd to allege that we do not enter into any obligation of not deceiving the enemy under color of treating with him: — it would be downright mockery, — it would be doing nothing. We are also bound to speak the truth to an enemy on all occasions when we are naturally obliged to it by the laws of humanity, — that is to say, whenever the success of our arms, and the duties we owe to ourselves, do not clash with the common duties of humanity, so as to suspend their force in the present case, and dispense with our performance of them. Thus, when we dismiss prisoners, either on ransom or exchange, it would be infamous to point out the worst road for their march, or to put them in a dangerous one; and should the hostile prince or general inquire after a woman or child who is dear to him, it would be scandalous to deceive him.

§ 178. Stratagems and artifices in war.
But when, by leading the enemy into an error, either by words in which we are not obliged to speak truth, or by some feint, we can gain an advantage in the war, which it would be lawful to seek by open force, it cannot be doubted that such a proceeding is perfectly justifiable. Nay, since humanity obliges us to prefer the gentlest methods in the prosecution of our rights — if, by a stratagem, by a feint void of perfidy, we can make ourselves masters of a strong place, surprise the enemy, and overcome him, it is much better, it is really more commendable, to succeed in this manner, than by a bloody siege or the carnage of a battle.5 But the desire to spare the effusion of blood will by no means authorize us to employ perfidy, the introduction of which would be attended with consequences of too dreadful a nature, and would deprive sovereigns, once embarked in war, of all means of treating together, or restoring peace (§ 174).

Deceptions practiced on an enemy, either by words or actions, but without perfidy, — snares laid for him consistent with the rights of war, — are stratagems, the use of which has always been acknowledged as lawful, and had often a great share in the glory of celebrated commanders. The king of England (William III) having discovered that one of his secretaries regularly sent intelligence of every thing to the hostile general, caused the traitor to be secretly put under arrest, and made him write to the duke of Luxembourg that the next day the allies would make a general forage, supported by a large body of infantry with cannon: and this artifice he employed for the purpose of surprising the French army at Steinkirk. But, through the activity of the French general, and the courage of his troops, though the measures were so artfully contrived, the success was not answerable.6

In the use of stratagems, we should respect not only the faith due to an enemy, but also the rights of humanity, and carefully avoid doing things the introduction of which would be pernicious to mankind. Since the commencement of hostilities between France and England, an English frigate is said to have appeared off Calais, and made signals of distress, with a view of decoying out some vessel, and actually seized a boat and some sailers who generously came to her assistance.7 If the fact be true, that unworthy stratagem deserves a severe punishment. It tends to damp a benevolent charity, which should be held so sacred in the eyes of mankind, and which is so laudable even between enemies. Besides, making signals of distress is asking assistance, and, by that very action, promising perfect security to those who give the friendly succor. Therefore the action attributed to that frigate implies an odious perfidy.

Some nations (even the Romans) for a long time professed to despise every kind of artifice, surprise, or stratagem in war; and others went so far as to send notice of the time and place they had chosen for giving battle.8 In this conduct there was more generosity than prudence, Such behavior would, indeed, be very laudable, if, as in the frenzy of duels, the only business was to display personal courage. But in war, the object is to defend our country, and by force to prosecute our rights which are unjustly withheld from us: and the surest means of obtaining our end are also the most commendable, provided they be not unlawful and odious in themselves.9 The contempt of artifice, stratagem, and surprise, proceeds often, as in the case of Achilles, from a noble confidence in personal valor and strength; and it must be owned that when we can defeat an enemy by open force, in a pitched battle, we may entertain a better-grounded belief that we have subdued him and compelled him to sue for peace, than if we had gained the advantage over him by surprise, — as Livy makes those generous senators say, who did not approve of the insincere mode of proceeding which had been adopted towards Persius, Therefore, when plain and open courage can secure the victory, there are occasions when it is preferable to artifice, because it procures to the state a greater and more permanent advantage.

§ 179. Spies.
The employment of spies is a kind of clandestine practice or deceit in war. These find means to insinuate themselves among the enemy, in order to discover the state of his affairs, to pry into his designs, and then give intelligence to their employer. Spies are generally condemned to capital punishment, and with great justice, since we have scarcely any other means of guarding against the mischief they may do us (§ 155). For this reason, a man of honor, who is unwilling to expose himself to an ignominious death from the hand of a common executioner, ever declines serving as a spy; and, moreover, he looks upon the office as unworthy of him, because it cannot be performed without some degree of treachery The sovereign, therefore, has no right to require such a service of his subjects, unless, perhaps, in some singular case, and that of the highest importance. It remains for him to hold out the temptation of a reward, as an inducement to mercenary souls to engage in the business. If those whom he employs make a voluntary tender of their services, or if they be neither subject to, nor in any wise connected with the enemy, he may unquestionably take advantage of their exertions, without any violation of justice or honor. But is it lawful, is it honorable, to solicit the enemy’s subjects to act as spies and betray him? To this question the following section will furnish an answer.

§ 180. Clandestine seduction of the enemy’s people.
It is asked, in general, whether it be lawful to seduce the enemy’s men, for the purpose of engaging them to transgress their duty by an infamous treachery? Here a distinction must be made between what is due to the enemy, notwithstanding the state of warfare, and what is required by the internal laws of conscience and the rules of propriety. We may lawfully endeavor to weaken the enemy by all possible means (§ 138), provided they do not affect the common safety of human society, as do poison and assassination (§ 155). Now, in seducing a subject to turn spy, or the governor of a town to deliver it up to us, we do not strike at the foundation of the common safety and welfare of mankind. Subjects acting as spies to an enemy, do not cause a fatal and unavoidable evil: it is possible to guard against them to a certain degree; and as to the security of fortresses, it is the sovereign’s business to be careful in the choice of the governors to whom he intrusts them. Those measures, therefore, are not contrary to the external law of nations; nor can the enemy complain of them as odious proceedings. Accordingly, they are practiced in all wars. But are they honorable, and compatible with the laws of a pure conscience? Certainly no; and of this the generals themselves are sensible, as they are never heard to boast of having practiced them. Seducing a subject to betray his country, engaging a traitor to set fire to a magazine, tampering with the fidelity of a governor, enticing him, persuading him to deliver up the town intrusted to his charge, is prompting such persons to commit detestable crimes. Is it honorable to corrupt our most inveterate enemy, and tempt him to the commission of a crime? If such practices are at all excusable, it can be only in a very just war, and when the immediate object is to save our country, when threatened with ruin by a lawless conqueror. On such an occasion (as it should seem) the guilt of the subject or general who should betray his sovereign when engaged in an evidently unjust cause, would not be of so very odious a nature. He who himself tramples upon justice and probity, deserves in his turn to feel the effects of wickedness and perfidy.10 And if ever it is excusable to depart from the strict rules of honor, it is against such an enemy and in such an extremity. The Romans, whose ideas concerning the rights of war were in general so pure and elevated, did not approve of such clandestine practices. They made no account of the consul Cæpio’s victory over Viriatus, because it had been obtained by means of bribery. Valerius Maximus asserts that it was stained with a double perfidy;11 and another historian says that the senate did not approve of it.12

§ 181. Whether the offers of a traitor may be accepted.
It is a different thing merely to accept of the offers of a traitor, we do not seduce him; and we may take advantage of his crime, while at the same time we detest it. Fugitives and deserters commit a crime against their sovereign; yet we receive and harbor them by the rights of war, as the civil law expresses it.13 If a governor sells himself, and offers for a sum of money to deliver up his town, shall we scruple to take advantage of his crime, and to obtain without danger what we have a right to take by force? But, when we feel ourselves able to succeed without the assistance of traitors, it is noble to reject their offers with detestation. The Romans, in their heroic ages, in those times when they used to display such illustrious examples of magnanimity and virtue, constantly rejected with indignation every advantage presented to them by the treachery of any of the enemy’s subjects. They not only acquainted Pyrrhus with the atrocious design of his physician, but also refused to take advantage of a less heinous crime, and sent back to the Falisci, bound and fettered, a traitor who had offered to deliver up the king’s children.14

But when intestine divisions prevail among the enemy, we may without scruple hold a correspondence with one of the parties, and avail ourselves of the right which they think they have to injure the opposite party. Thus, we promote our own interests, without seducing any person, or being in anywise partakers of his guilt. If we take advantage of his error, this is doubtless allowable against an enemy.

§ 182. Deceitful intelligence.
Deceitful intelligence is that of a man who feigns to betray his own party, with a view of drawing the enemy into a snare. If he does this deliberately, and has himself made the first overtures, it is treachery, and an infamous procedure: but an officer, or the governor of a town, when tampered with by the enemy, may, on certain occasions, lawfully feign acquiescence to the proposal with a view to deceive the seducer: an insult is offered to him in tempting his fidelity; and to draw the tempter into the snare, is no more than a just vengeance. By this conduct he neither violates the faith of promises nor impairs the happiness of mankind: for criminal engagements are absolutely void, and ought never to be fulfilled; and it would be a fortunate circumstance if the promises of traitors could never be relied on, but were on all sides surrounded with uncertainties and dangers. Therefore a superior, on information that the enemy is tempting the fidelity of an officer or soldier, makes no scruple of ordering that subaltern to feign himself gained over, and to arrange his pretended treachery so as to draw the enemy into an ambuscade. The subaltern is obliged to obey. But when a direct attempt is made to seduce the commander-in-chief, a man of honor generally prefers, and ought to prefer, the alternative of explicitly and indignantly rejecting so disgraceful a proposal.15


     1.    De salute ceriatum est.
     2.    To this doctrine, the prohibition of subjects of belligerent states having commercial contracts with each other, and the prohibition in Great Britain of contracts of ransom, constitute exceptions, post. 403-4 4. C.
     3.    Histoire de Guillaume III tom. ii. p.
     4.    Falsiloquium, false speaking, untruth, falsehood.
     5.    There was a time when those who were taken in attempting to surprise a town, were put to death. In 1597, prince Maurice attempted to take Venloo by surprise: the attempt failed; and some of his men, being made prisoners on the occasion, “were condemned to death, — the mutual consent of the parties having introduced that new rule, in order to obviate dangers of this kind.” (Grotius Hist. of the Disturb, in the Netherlands.) Since that time, the rule has been changed: at present, military men who attempt to surprise a town in time of open war, are not, in case of being taken, treated in a different manner from other prisoners: and this custom is more consonant to reason and humanity. Nevertheless, if they were in disguise, or had employed treachery, they would be treated as spies; and this is, perhaps, what Grotius means; for I do not, in any other instance, find that such severity was used towards troops who were simply come to surprise a town in the silence of the night. It would be quite another affair, if such an attempt were made in time of profound peace; and the Savoyards, who were taken in the escalade of Geneva, deserved the punishment of death which was inflicted on them. [See page 321.]      6.    Mémoires de Feuquléres, tom. iii. p. 87.
     7.    See an instance of similar baseness, Baumann, 1 Rob. Rep. 245; ante, § 69, page 321. — C.
     8.    This was the practice of the ancient Gauls. See Livy. — It is said of Achilles, that he was for fighting openly, and not of a disposition to conceal himself in the famous wooden horse, which proved fatal to the Trojans: — Ille non, inclosus equo Minervæ Sacra mentito, male feriatos Troas, et lætam Priami choreis Falleret aulam; Sed palam captis gravis. Hor. lib. iv. od. 6
     9.    Virg. æn. ii. 390. § Tit Liv. lib. xlii. cap. 47
     10.    Xenophon very properly expresses the reasons which render treachery detestable, and which authorize us to repress it by other means than open force. “Treachery,” says he, “is more dreadful than open war, in proportion as it is more difficult to guard against clandestine plots than against an open attack: it is also more odious, because men engaged in overt hostilities may again treat together, and come to a sincere reconciliation; whereas nobody can venture to treat with or repose any confidence in a man whom he has once found guilty of treachery.” — Hist. Graw. lib. ii. cap. 3.
     11.    Viriati etiam cædes duplicem perdiæ accusationem recepit, in amicis, quod eorum manibus interemptus est, in Q. Servilio Caepione consule, qula is sceleris hujus, auctor, impunita te promissa, full, victoriamque non meruit sed emit. — Lib. ix. cap. 6. — Although this instance seems to belong to another head (that of assassination), I nevertheless quote it here, because it does not appear, from other authors, that Cæpio had induced Viratus’s soldiers to assassinate him. Among others, see Eutropius, lib. vi. cap. 8.
     12.    Quæ victoria, qula empta erat, a senatu non probata. Auctor de Viris Illust. cap. 71.
     13.    Transfugam jure belli recipimus. Digest 1. xli. tit. 1, de adquir. Rer. Dom. leg. 51.
     14.    Eâdem fide indicatum Pyrrho regi medicum vitæ ejus insidiantem; eâdem Faliscis vinctum traditum proditorem liberorum regis. Tit. Liv. lib. xlii. cap. 47
     15.    When the duke of Parma was engaged in the siege of Bergen-op-zoom, two Spanish prisoners, who were confined in a fort near the town, attempted to gain over a tavern-keeper, and an English soldier, to betray that fort to the duke. These men, having acquainted the governor with the circumstance, received orders from him to feign acquiescence; and, accordingly, having made all their arrangements with the duke of Parma for the surprisal of the fort, they gave notice of every particular to the governor. He, in consequence, kept himself prepared to give a proper reception to the Spaniards, who fell into the snare, and lost near three thousand men on the occasion. — Grotius, Hist, of the disturb, in the Netherlands, book i.