Siris: On Subsidiarity: The first thing to understand about the principle of subsidiarity, or the principle of subsidiary function, is that it gives exactly what the label says. It is, in Benedict XVI's words, "a form of assistance to the human person via the autonomy of intermediate bodies" (Caritas in Veritate). The word 'assistance' is key here; subsidiarity is literally helpfulness (subsidium is Latin for 'help, aid, assistance'), and if we didn't like the latinate name we could simply, and with complete accuracy, call it the Helpful Function Principle or the Helpfulness Principle. It's clearly this that's front and center with the famous passage from Quadragesimo Anno:
Just as it is gravely wrong to take from individuals what they can accomplish by their own initiative and industry and give it to the community, so also it is an injustice and at the same time a grave evil and disturbance of right order to assign to a greater and higher association what lesser and subordinate organizations can do. For every social activity ought of its very nature to furnish help to the members of the body social, and never destroy and absorb them.