Why do practitioners call the Dao De Jing a Nei Dan classic when the academics say Nei Dan was invented much later?
The oral history of Taoism states that what we call Nei Dan (Internal Alchmey) has its origins in the mists of Taoist history – dating back to Huang Di and Lao Zi (Huang-Lao Taoism). Although western trained historians and sinologists tend to base their dating of what we call Nei Dan practices to a much later period (roughly the Tang Dynasty), the Internal Alchemy practitioners recognize that alchemy practices are much older.
This difference in perspective is due in part to the conventions of academic research based upon the historical usage of specific terms and other indicators. For example, a western trained historical might ask “When did the specific language of Nei Dan appear?” and date it accordingly. In contract, actual practitioners tend to use the term Nei Dan less formally and apply it to a group of closely related self-cultivation practices.
These practices are described in the Chinese classic texts such as the Yi Jing, Dao De Jing, Zhuang Zi and Nei Yeh. The Tang Dynasty Nei Dan texts use a slightly different metaphorical system, one based on the language of External Alchemy. However, they are describing the same thing. In other words, to the practitioners, “A rose by any other name is still a rose.”
For this reason, the Dao De Jing (DDJ) is considered the most important foundation Nei Dan text, in the common usage of that term. That is because it is an internal cultivation text which describes methods that ultimately produce the same effect as Nei Dan, which is “uniting with the Tao” “perfection” or “immortality”. In this case, the text does indeed stand alone. For example, Chapters 2, 3, 5 and 6 are thought to provide fairly specific advice on how to cultivate. Some practitioners consider that Chapter 3 “…The sage empties the heart and fills the belly…” is the basis for the two major lines of Taoist internal cultivation.
This, of course, does not preclude the text from being read as applying to all other activities in this world — “As above, so below.” If anything, its application to other areas strengthens its value as a guide to inner cultivation. That is because ordering your life’s affairs is one of the major prerequisites for an aspiring practitioner to begin their training.
To state it a little more formally, you can consider the practices of cultivation aimed at “uniting with the Tao” in general as an umbrella concept. Underneath it you can recognize various subsets of this cultivation. These subsets may consist of methods characterized by historically specific identifiers e.g. Nei Dan.
Following this line you could even say that Ritual is itself one of the subsets of “immortality” cultivation. One of the many “vehicles” to borrow a Buddhist term.