Espionage, old as war itself, has always occupied a morally ambiguous position. Referenced in the book of Joshua, Christians have long struggled to apply clear moral principles to espionage. While Just War Theory as articulated by St. Thomas Aquinas offers some clarity in this regard, it falls short of addressing the moral complexities of espionage in the 21st century, specifically declaring espionage, the problem of deception, and the targeting of non-combatants, all areas where further scholarship is necessary.

St. Thomas Aquinas is arguably the first Christian theologian to have expressed a systematic, Christian view of war based on Church Tradition and Sacred Scripture. In Part II, Question 40, Article 1, he lays out three principles for jus ad bellum, or the conditions under which a state can legitimately declare war. These are: (1) that the state declaring war must have legitimate authority to do so; (2) that the state has a just cause; and (3) that the state has a rightful intention. A rightful intention, as St. Thomas Aquinas put it, is not “motives of aggrandizement, or cruelty, but with the object of securing peace, of punishing evildoers, and of uplifting the good.” No war can be called just absent any of these conditions. However, while these principles have been consistently applied to various conflicts throughout history, they cannot be applied to the spying of today.

The primary difficulty lies with the fact that countries do not declare their intent to engage in espionage as they declare war. For espionage to be effective there can be no start or end date. Espionage is an ongoing process meant to provide a base of knowledge by which a state can identify threats as or before they emerge. As espionage is necessarily an ongoing process, the second two principles for jus in bellum, namely, just cause and rightful intention, cannot be conclusively applied. Aquinas relies on St. Augustine when defining what constitutes a just cause. “A just war is wont to be described as one that avenges wrongs, when a nation or state has to be punished, for refusing to make amends for the wrongs inflicted by its subjects, or to restore what it has seized unjustly.” Some intelligence-gathering activity responds to wrongs inflicted on a state’s subjects. For example, following 9/11, the Patriot Act was passed, enlarging the government’s abilities to engage in intelligence gathering activities. However, it should be noted that this was an increase, not the commencement of intelligence gathering meant to prevent terror attacks. Given that espionage is mostly preventative, the principle of just cause is not well suited to an analysis of spying. Distinctions can be made between espionage intended to protect innocent citizens, espionage meant to maintain order and uphold governments, and espionage meant to protect corrupt regimes. However, the distinction between maintaining order and safeguarding corrupt regimes is not always clear. The same issue applies in determining right intention. The preventative nature of espionage means right intention of securing peace, punishing evildoers, and promoting the common good often does not apply. Intelligence gathering occurs in peace as well as war and, when discovered, is seen as an act of aggression.

In addition to the problems with applying jus ad bellum principles to espionage, there are also issues with the jus in bello considerations, or right conduct in war. These principles were developed after Aquinas; however, St. Thomas Aquinas specifically addresses deception in warfare, which is particularly relevant in espionage. Aquinas distinguishes between soldiers concealing their purpose from the enemy in a campaign of war and soldiers or states lying or breaking promises. Concealment is perfectly acceptable in warfare – God Himself instructed Joshua to lay ambushes for the city of Hai in Joshua 8:2, and Esther hides her Jewish identity from King Xerxes to save her people. Lying and breaking promises, however, are intrinsically immoral. Espionage blurs the distinction between the two while relying heavily on both. Is it a lie to assume a false identity to infiltrate a terror group, or is it concealment? Is it a lie to give false information about oneself or something else, or is it concealment? Intelligence gathering relies more on SIGINT (signal intelligence) and less on HUMINT (human intelligence, i.e. spies in the field) than it did in the past. However, recent intelligence failures, such as the October 7th attack in Israel, have demonstrated the crucial role of HUMINT. Thus, this distinction remains foundational to morality in espionage.

Finally, although not explicitly stated by Aquinas, Just War Theory in the Christian tradition makes an important distinction between the just treatment of combatants and non-combatants in war. Non-combatants may never be directly targeted in war, even if they are unintentionally harmed in war. Combatants, on the other hand, can be intentionally killed in war. Espionage does not make this distinction between directly targeting combatants and non-combatants in harmful ways like opening mail, blackmailing, recording conversations, etc. While not death (and thus not as morally grave), all of these take a moral toll on innocent civilians. While just war theory makes room for innocents dying in a siege of a fortress, for example, there is a difference between innocents dying in a siege and innocents being spied upon. Despite these issues with the application of Just War Theory to contemporary espionage, Christians should not throw the baby out with the bathwater. Intelligence gathering poses moral challenges that Just War Theory alone cannot resolve; nevertheless, it is an essential part of statecraft and of war in the 21st century. Just War principles should be the basis for a new systematic approach to understanding morality in espionage. As the world secularizes questions of politics and morality, it is the role of the Church and Christian communities to take these questions to the Cross.