The theory of

yuan

qi was first put forward in

Chunqiu Fanlu

in the Western Han Dynasty

and considered as formed the early natural philosophy of Confucianism. However

in

Huangdi Neijing (Huangdi's Internal

Classics)

except for the seven major treatises on

yunqi

theory in the Eastern Han Dynasty that were added in later generations

the character "

yuan

" in its text didn't have the equivalent philosophical connotation to the root theory yet. After the Eastern Han Dynasty

there was overlapping between "

yuan

qi" and "

zhen

qi" in the generative theory

so the widely-used word "

yuan

qi"was used to replace or integrate the concept of "

zhen

qi". Nevertheless

yuan

qi and

zhen

qi have different philosophical origins. The

yuan

qi thought was rooted in Confucianism in the Western Han Dynasty

while the

zhen

qi thought originated from Taoism in the pre-Qin Dynasty. It is "

zhen

qi" rather than "

yuan

qi" that is the core concept of the root theory in Huangdi Neijing.