In addition
to the various statements regarding emptiness, Buddha-nature and thusness, which
conform in every respect to the commonly accepted teachings of all the chan schools,
Dongshan also develops the teaching of the Five Ranks, represented in the Sung histories as
the characterizing philosophical doctrine of the emergent Cao-Dong School. The Five Ranks
of Dongshan are a set of five modes in which apparent or phenomenal reality interacts with
ultimate or absolute reality. In traditional Buddhist terms, the teaching demonstrates five
possibilities for the construction of form and emptiness. In traditional Chinese terms, the
Five Ranks show the interactive relations of li (principle) and shi (phenomena). The recorded
teachings of Caoshan Benji likewise indicate the importance of the Five Ranks in the early
years of Cao-Dong School. They contain extensive elaboration, through the systematic use
of metaphor and symbol, of Dongshan's original theory.
...
Its [the Five Rank's] popularity and employment as a teaching device seems to have varied
enormously from generation to generation – Dogen Zenji seems to have been little
impressed with it – but it is reasonable to say that it has always had at the very least a
background presence throughout the later history of Cao-Dong School. Indeed the Sungperiod
chan histories agree in emphasizing Dongshan's Five Ranks as the original teaching
of the school, which alone probably would have precluded the possibility of its complete
disappearance afterwards