Yolŋu understand the world in terms of their relationship to it. Their whole universe is permeated by the fundamental social and spiritual division of two moieties: Dhuwa and Yirritja. Everything in the world is either Dhuwa or Yirritja, never both. The world is then further divided according to clan affiliations and relationships between clans, both within and across moieties. People thus have special relationships not only with their own clan's country but with their mother's country or their grandmother's country.
"Particular individuals and groups of people have special connections with particular areas of land and sea, animals, plants, ceremonies and creation stories." N. Munuŋgiritj 
The differentiation of the world into Dhuwa and Yirritja can be seen as the beginning point of Yolŋu classification. However Yolŋu also have complex ways of classifying the natural world that cross-cut moiety and clan divisions.
John Rudder's analysis  of Yolŋu ways of categorising species according their physical characteristics, use, and the environments in which they live, reflects the complexity of Yolŋu understandings of the world.