Thomism Goes to War

Heritage Hall in Father O'Connell Hall, The Catholic University of America

Join the IHE for its second Annual Lecture on Catholic Political Thought. Dr. Gregory M. Reichberg will give this year’s lecture, “Thomism Goes to War.” 

Saint Thomas Aquinas is often credited, alongside Saint Augustine, with being the initiator of what has come to be called the “just war tradition.” Indeed, Aquinas’s short Summa Theologiae article (II-II, q. 40, a. 1) “whether any war is licit,” has spawned many pages of commentary. It remains a key point of reference up to the present day.

Curiously, however, Aquinas had little to say about the wars of his own time. We rarely find him applying his famous three criteria (legitimate authority, just cause, right intention) to assess, for instance, the crusades or other armed initiatives then underway.

Nonetheless the realities of armed conflict were brought very close to home when his older brother Reynaud, a knight at the service of the pope, was executed by the emperor’s troops. This led Aquinas to reflect on whether holy martyrdom could apply to soldiers fallen in battle. Subsequent Thomists have followed his example and brought their thought to bear on concrete matters of war.

Dr. Gregory M. Reichberg will review some of these engagements (vis-à-vis the conquest of the New World, the Spanish Civil War, and the Second World War) and indicate what lessons can be drawn for us today.



Gregory M. Reichberg is Research Professor at the Peace Research Institute Oslo (PRIO). He previously served as a faculty member in the School of Philosophy at The Catholic University of America.

He leads Warring with Machines: Military Applications of Artificial Intelligence and the Relevance of Virtue Ethics, a four-year project funded by the Research Council of Norway’s Research Programme on the Cultural Conditions Underlying Social Change (SAMKUL).

His writings include a monograph Thomas Aquinas on War and Peace (Cambridge University Press, 2017), named an “Outstanding Academic Title 2017” by Choice magazine.

He has also published several co-edited volumes, including Robotics, AI, and Humanity: Science, Ethics, and Policy (Springer, 2021); Religion, War, and Ethics: A Sourcebook of Textual Traditions (Cambridge University Press, 2014); World Religions and Norms of War (United Nations University Press, 2009); and The Ethics of War: Classic and Contemporary Readings (Blackwell Publishing, 2006).

His recent publications include a co-authored book chapter “AI in Cyber Operations: Ethical and Legal Considerations for End-Users (in Artificial Intelligence and Cybersecurity, Springer, 2023); “Applying AI on the Battlefield: The Ethical Debates” (with Henrik Syse), in Robotics, AI, and Humanity (Springer, 2021); “Philosophical Debate on Deterrence,” in Forbidden: Receiving Pope Francis’s Condemnation of Nuclear Weapons (Georgetown University Press, 2023), and “From the Nuclear Family to the Family of Nations: Exploring the Analogy,” in The Family as Relational Good: The Challenge of Love (Libreria Editrice Vaticana, 2023).

From 2012-2020 he headed the Oslo-based Research School on Peace and Conflict, and from 2009-2012 he was director of the PRIO Cyprus Centre in Nicosia, where he coordinated research and dialogue activities on the search for a political settlement to the island’s division.

Dr. Reichberg has been an Ordinarius in the Pontifical Academy of Social Sciences since 2016. In 2021 he was appointed consultor to the Holy See’s Dicastery for Promoting Integral Human Development, headquartered in Vatican City. His contribution focuses on disarmament, the ethical implications of new military technologies, and broader issues of war and peace.