9 Any well-regulated and productive association of men in society demands the acceptance of one fundamental principle: that each individual man is truly a person. His is a nature, that is, endowed with intelligence and free will. As such he has rights and duties, which together flow as a direct consequence from his nature. These rights and duties are universal and inviolable, and therefore altogether inalienable. (7)
Source: Pacem in Terris (Vatican.va)