‘That thread from Leo XIII to Leo XIV’ is the title of an article by Roberto Regoli published in the monthly magazine “Formiche” (Rubbettino, August–September 2026, pages 48–49). In the article, the author highlights the fact that the Church’s social doctrine develops in a spirit of continuity: a journey which, from the labour question to the challenges of artificial intelligence, keeps at its heart the dignity of the person, the common good and the relationship between faith and reason.

Taken from “Formiche”

That thread from Leo XIII to Leo XIV

by Roberto Regoli, President of the Joseph Ratzinger – Benedetto XVI Vatican Foundation and Full Professor of Contemporary History at the Pontifical Gregorian University.

The social teaching of the popes is best understood in terms of continuity. From Leo XIII to Leo XIV, a body of doctrines has been built up which are consistent with one another, with differences arising from new insights and clarifications. It is for this reason that Pope Prevost issues this encyclical to address not only artificial intelligence, but the whole of Catholic social teaching as it applies to the new challenges of the 21st century, guided by the dignity of the human person, human reason and intelligence enlightened by faith. Faced with socio-political challenges, the popes have responded with their teaching (magisterium), particularly following a document by Pope Leo XIII, the 1891 encyclical *Rerum novarum*, which sought to address the so-called social question arising from the Industrial Revolution. With Pius XI (the encyclical *Quadragesimo anno* of 1931), the term ‘Social Doctrine’ came to denote the body of teaching specifically concerning issues of social relevance.

These are often contingent issues, which may receive equally contingent responses. And for this reason, Social Doctrine—beyond its statements of principle—is frequently highly variable in its application. It cannot be otherwise. Let us take a specific example: that of migration policies. According to the Catechism of the Catholic Church, ‘political authorities, in view of the common good for which they are responsible, may make the exercise of the right to immigration subject to various legal conditions, in particular to the fulfilment of the duties of

migrants towards the host country’ (Art. 2241). The phrase ‘various legal conditions’ precisely highlights the contingent nature of responses over time. The popes speak and write, but ultimately the responsibility lies entirely with politicians. It must be acknowledged that the popes have tended to follow rather than anticipate the debate on social issues.

This is hardly surprising, as Rome plays a coordinating role – an authoritative role as the body that steers the debate and utters the decisive words. Rome rarely takes the lead, and on social matters it has mostly arrived late to the debate. Nevertheless, its responses remain central. The social teaching of the popes is understood in terms of continuity. From Leo XIII to Leo XIV, a body of mutually consistent doctrines has been established, and any differences have stemmed from new insights and clarifications.

Consider the issue of the death penalty, which, owing to new conceptions of human dignity and the limits of state power, has been banished from Catholic thought (under Pope Francis), having previously been recognised as a possibility in more recent times. Other issues, too, have evolved over time. Take the issue of peace, which the popes continually

point to as the horizon of human coexistence: from the statements of Benedict XV and Pius XII during the world wars—who believed all was lost through conflict—to those of Leo XIV, who spoke of a peace that is both unarmed and disarming. John Paul II, through the Assisi meetings, sought to involve all religions in a dialogue for peace (even after 11 September 2001), and Benedict XVI extended this commitment not only to religions but to all ethical systems, including those of non-believers. And standing out amidst all this is the principle of the ‘just war’, which speaks of defence rather than offence, of an intervention proportionate to the aggression, deemed to be successful (Catechism of the Catholic Church, 2309). This principle has been invoked to justify Ukraine’s response to Russia, but not the American-Israeli intervention in Iran.

Leo XIV, in his encyclical *Magnifica humanitas*, discusses this principle, emphasising that it cannot be exploited to justify any war (192). On the other hand, Catholicism distinguishes between violence and the use of force, to the extent that the Second Vatican Council itself speaks in praise of the military (“they too should be regarded as servants of the security and freedom of their peoples; if they fulfil their duty rightly, they too truly contribute to the stability of peace”, *Gaudium et spes* (79).

Certain principles have been reaffirmed over time. One need only think of Pius XI, who articulated the principle of subsidiarity, which was to become a permanent feature of Social Doctrine. In terms of continuity, we also find condemnations of totalitarianism, from Pius XI right up to the present day. The popes attach great importance to the relationship between law and morality, particularly from the pontificate of Pius XII onwards, who placed great emphasis on the notion of natural law—a concept borrowed from Leo XIII—which is also found in subsequent pontificates, right up to

Leo XIV, to justify the public interventions of Catholicism, which are to be understood not from the perspective of a theocracy, but in accordance with the demands of human reason itself, which Benedict XVI regards as open.

There is a core set of principles presented as ‘non-negotiable values’ by Benedict XVI, which Leo XIV regards as closely linked to the common good. It is for this reason that in 2026 Pope Prevost issued *Magnifica humanitas* to address not only artificial intelligence (as had previously been the case in the great

public), but of the whole of Catholic social teaching applied to the new challenges of the 21st century (including artificial intelligence, but not limited to it), taking as its criterion the dignity of the human person, understood in terms of human reason and intelligence enlightened by faith. A discourse consistent with everything that preceded it. This is the Social Doctrine of the Catholic Church.

MILESTONES_ Over a century of Social Doctrine With *Rerum novarum* in 1891, Leo XIII inaugurated the social teaching of the Church, offering a Christian response to the labour question. Since then, Social Doctrine has accompanied the world’s great transformations: Pius XI developed the principle of subsidiarity during the crisis of the 1930s; John XXIII and the Second Vatican Council placed rights, peace and dialogue at the centre; Paul VI linked development and justice; John Paul II reflected on work, solidarity and democracy; Benedict XVI interpreted globalisation; and Francis integrates the environment, fraternity and care for our common home.