Listers, in his third article discussing war, St. Thomas Aquinas raises a question of “just tactics” or rather whether or not ambushes and other “deceptive” maneuvers are permissible in a just war. The Angelic Doctor speaks of war under the heading of those things which are contrary to peace, and peace is listed as a species of charity, the mother of all virtues.1
Whether it is lawful to lay ambushes in war?
The following three objections are opinions NOT held by ST. Thomas, but raised by him in order to better understand the position of others. The entire Summa Theologica is in a question and answer format - which is the most natural form of education. The titles have been added.
1. If it is deceptive, is it not unjust?
Objection 1. It would seem that it is unlawful to lay ambushes in war. For it is written (Deuteronomy 16:20): “Thou shalt follow justly after that which is just.” But ambushes, since they are a kind of deception, seem to pertain to injustice. Therefore it is unlawful to lay ambushes even in a just war.
2. If it is a form of lying, is it not unjust?
Objection 2. Further, ambushes and deception seem to be opposed to faithfulness even as lies are. But since we are bound to keep faith with all men, it is wrong to lie to anyone, as Augustine states (Contra Mend. xv). Therefore, as one is bound to keep faith with one’s enemy, as Augustine states (Ep. ad Bonif. clxxxix), it seems that it is unlawful to lay ambushes for one’s enemies.
3. If we love our enemies, how can we deceive?
Objection 3. Further, it is written (Matthew 7:12): “Whatsoever you would that men should do to you, do you also to them”: and we ought to observe this in all our dealings with our neighbor. Now our enemy is our neighbor. Therefore, since no man wishes ambushes or deceptions to be prepared for himself, it seems that no one ought to carry on war by laying ambushes.
St. Thomas’ Response
4. On the Authority of Scripture
On the contrary, Augustine says (QQ. in Hept. qu. x super Jos): “Provided the war be just, it is no concern of justice whether it be carried on openly or by ambushes”: and he proves this by the authority of the Lord, Who commanded Joshua to lay ambushes for the city of Hai (Joshua 8:2).
5. Rights and Covenants of War
I answer that, The object of laying ambushes is in order to deceive the enemy. Now a man may be deceived by another’s word or deed in two ways. First, through being told something false, or through the breaking of a promise, and this is always unlawful. No one ought to deceive the enemy in this way, for there are certain “rights of war and covenants, which ought to be observed even among enemies,” as Ambrose states (De Officiis i).
6. The Lawful Art of Concealment
Secondly, a man may be deceived by what we say or do, because we do not declare our purpose or meaning to him. Now we are not always bound to do this, since even in the Sacred Doctrine many things have to be concealed, especially from unbelievers, lest they deride it, according to Matthew 7:6: “Give not that which is holy, to dogs.” Wherefore much more ought the plan of campaign to be hidden from the enemy. For this reason among other things that a soldier has to learn is the art of concealing his purpose lest it come to the enemy’s knowledge, as stated in the Book on Strategy [Stratagematum i, 1 by Frontinus]. Such like concealment is what is meant by an ambush which may be lawfully employed in a just war.
Nor can these ambushes be properly called deceptions, nor are they contrary to justice or to a well-ordered will. For a man would have an inordinate will if he were unwilling that others should hide anything from him
This suffices for the Replies to the Objections.