Quadragesimo anno of 1931 gives the principle a classic papal formulation. Its setting includes the concentration of economic power and the growth of states that sought to control social life. The principle defends the real functions of families, local communities and associations against the assumption that all effective action should be transferred to a central authority.
Subsidiarity is not a prohibition of public intervention. A smaller body may lack the resources or power needed to protect its members. Assistance and legal protection can then be necessary. The larger authority should act in a way that serves the common good and, where possible, strengthens the agency of those receiving help. Permanent dependency and unnecessary displacement are dangers to be assessed.
The principle belongs with solidarity rather than against it. Families and associations have responsibilities toward others; they are not private enclaves exempt from justice. Public power likewise has duties toward the weak. The question is how those duties are distributed and coordinated without reducing society to isolated individuals facing an all-controlling state.
Historically, Catholic workers’ associations, educational institutions and charitable organisations embodied forms of intermediate life. Their performance varied, but their existence challenged both economic individualism and political totalism. Catholic apologetics can therefore defend independent institutions while still judging whether they actually serve their members and the wider common good. A privileged association that neglects justice cannot invoke subsidiarity as a shield against every legitimate correction.