Although the roots of subsidiarity predate Christianity, we can usefully explore encyclical teaching to appreciate how the Catholic Church has given intelligible expression to this concept in the midst of her broader social teaching. The paradox of subsidiarity is that it mandates contradictory things: requiring on the one hand that the state should not interfere with the internal life of civic associations and on the other hand that the state should provide assistance to those associations when such assistance is necessary. Rather than using the language of "positive" and "negative" subsidiarity (which, it is argued, is not especially helpful because it perpetuates the sovereigntist tendency to see the state as the locus of all authority), this chapter focuses on how the encyclicals illuminate (1) the nature of subsidiarity, as neither freestanding nor abstract; (2) subsidiarity’s political purposes (increased participation in decision making by actors who are more proximate to need and therefore better placed to reach good outcomes more efficiently), moral purposes (protection of associational freedom and avoidance of totalitarianism), and final purposes (protection of that charity which can never be mediated through bureaucracies); and (3) the operationalisation of subsidiarity, which can be promoted or inhibited through the action of law.

The common good (bonum commune) has, since antiquity, referred to the aim of social and political association, and was particularly prominent in medieval Christian political theology. Since St. John XXIII’s 1961 encyclical letter, Mater et magistra, ecclesiastical statements about social teaching have employed a formulation of the common good, usually in the version that appeared in the Second Vatican Council’s 1965 Pastoral Constitution for the Church in the Modern World, Gaudium et spes, as “the sum of those conditions of social life that allow social groups and their individual members relatively thorough and ready access to their own fulfillment.” This chapter discusses the origins and development of this formulation as well as the ways that it has been used in subsequent Catholic Social Teaching. While it has sometimes been interpreted as an “instrumental” account of the common good, the sources and uses of the notion suggest that it is the particularly modern political component of a fuller notion of the common good continuous with the tradition. In particular, the recent formulation is concerned to limit the power of the modern state and protect the dignity of the human person in the challenging conditions of political modernity.