The text is from Suwen-Biaoben Bingchuan Lun. It is a principle for determining treatment by distinguishing the primary and secondary, root and branch, severity, and urgency of the disease. The concept of "root and branch" has multiple meanings: in terms of the human body and disease-causing factors, the body's healthy qi is the root, while the pathogenic qi is the branch; in terms of the disease itself, the cause is the root, and the symptoms are the branch; in terms of the newness and oldness of the disease, as well as primary and secondary conditions, the old and primary disease is the root, while the new and secondary disease is the branch; in terms of the location of the disease, the internal is the root, and the external is the branch. Clinically, based on the different conditions of the disease, the main contradiction is identified from the relationship between root and branch, and appropriate treatment is administered.