Various circumstances may make it advisable that the State step in to supply certain functions [401]. One may think, for example, of situations in which it is necessary for the State itself to stimulate the economy because it is impossible for civil society to support initiatives on its own. One may also envision the reality of serious social imbalance or injustice where only the intervention of the public authority can create conditions of greater equality, justice and peace. In light of the principle of subsidiarity, however, this institutional substitution must not continue any longer than is absolutely necessary, since justification for such intervention is found only in the exceptional nature of the situation. In any case, the common good correctly understood, the demands of which will never in any way be contrary to the defence and promotion of the primacy of the person and the way this is expressed in society, must remain the criteria for making decisions concerning the application of the principle of subsidiarity.
Compendium of the Social Doctrine of the Church, no. 188