One advantage of exhibiting a hierarchy of systems in this way is that it gives us some idea of the present gaps in both theoretical and empirical knowledge. Adequate theoretical models extend up to about the fourth level, and not much beyond. Empirical knowledge is deficient at practically all levels.
Kenneth E. BouldingThe right to have children should be a marketable commodity, bought and traded by individuals but absolutely limited by the state.
Kenneth E. Boulding