Overarching Three Yin-Three Yang: Evolution of the Basics

Abstract: The three yin-three yang (三阴三阳, 3Y-3Y) system in traditional Chinese medicine (TCM) represents a distinct evolution from the earlier yin-yang (阴阳) theory that had astronomical applications. This system was used specifically for the body channels. One needs to unveil the missing elements of its early evolution, as the understanding of how the 3Y-3Y system was derived prior to the observation-based 11 meridians remain unclear. By integrating historical and archaeological sources and using an interdisciplinary approach that links cosmology, body movements, and meridian development, the missing conceptual elements can be retraced. Early observation-based body mechanics and movements were viewed through the yin-yang framework. The initial culture focused on a “tripodal system” of yang movements in the lower body, which is evidenced by the more primitive Shuangbaoshan (双包山) figurine that depicts three yang lines on the legs but lacks yin lines. The earliest texts, such as Zu Bi Shi Yi Mai Jiu Jing (《足臂十一脉灸经》 Moxibustion Canon of Leg and Arm Eleven-channels ), also prioritized the limbs, suggesting body movement was probably the primary derivative. The three yang lines were likely named based on the body parts that received the most sunlight. As yin encompasses a broader range of concepts, the setting of the three yin meridians was more complex and developed somewhat later. For a time, the meridian system was not fully correlated with the internal organs, and early models—even the Shuangbaoshan figurine—were missing the leg’s yin lines entirely. It is proposed that the lateral yang line and the Jue yin (厥阴) line together could have be more meaningful. Understanding the incremental progress—from cosmological yin-yang, to understanding the body in yin-yang, to body movements in yin-yang, to body tripodal yin-yang, and then to the transitory 2Y-3Y+3Y-3Y upper plus lower meridians—is significant for TCM history. This progression culminated in the conceptual leap to a complete 3Y-3Y system, a development created a balanced model that harmonizes the body with the cosmos yin-yang cycles.