50 The consciousness of his own weakness urges man to call in aid from without. We read in the pages of holy Writ: "It is better that two should be together than one; for they have the advantage of their society. If one fall he shall be supported by the other. Woe to him that is alone, for when he falleth he hath none to lift him up."(34) And further: "A brother that is helped by his brother is like a strong city."(35) It is this natural impulse which binds men together in civil society; and it is likewise this which leads them to join together in associations which are, it is true, lesser and not independent societies, but, nevertheless, real societies.
Source: Rerum Novarum (Vatican.va)