Early Heaven and Later Heaven Eight Trigrams
The Eight Trigrams are represented by two arrangements, one being known as the Early Heaven Eight Trigrams (先天八卦), and the other being the Later Heaven Eight Trigrams (后天八卦). Early Heaven Eight Trigrams depicts an innate state whereby Yin and Yang are mutually opposing yet complementary and balanced. One widely known verse describes the Early Heaven Eight Trigrams based on the eight natural phenomena of Nature; Heaven and Earth fixing position (天地定位), Mountain and Lake interconnection of Qi (山泽通气), Thunder and Wind mutually arousing (雷风相薄), Water and Fire non conflicting (水火不相射).
Note: Depiction of Early Heaven Eight Trigrams arrangement on a Nine Palaces (九宫) format on the right.
From the Early Heaven Eight Trigrams arrangement, we can see that each pairs of opposing Trigrams are exact opposite in terms of Yin Yang but this also illustrates the complementary and harmony aspect of Yin Yang.
On the other hand, Later Heaven Eight Trigrams depicts the locational, directional, dynamic and cyclical Qi flow of the Five Elements. It deals with changes brought on by the passing of time. It shows the continuous birth, flourish, decline and death process of Nature.
Zhen Trigram (wood) signifies the season of spring, the rising of the Sun in the east and sprouting of life and beginnings. Xun Trigram (wood) signifies the coming of summer, and the growing of trees in unison. Li Trigram (fire) signifies the season of summer, the flourishing of trees and the brilliance of the Sun. Kun Trigram (earth) signifies the coming of autumn, the maturation of trees and the nurturing nature of earth. Dui Trigram (metal) signifies the season of autumn, the shedding of leaves and time of harvesting. Qian Trigram (metal) signifies the coming of winter and the entering of the cold from nightfall. Kan Trigram (water) signifies the season of winter and the hibernation of trees and beings. Gen Trigram (earth) signifies the coming of spring, the completion of things but also the preparation of new beginnings.
And, combining the Later Heaven Eight Trigrams with the eight directions, we have Kan Trigram representing the north direction, Li Trigram representing the south direction, Zhen Trigram representing the east direction, Dui Trigram representing the west direction, etc.
The correct understanding and clarity between the Early Heaven and Later Heaven Eight Trigrams is very important, whether with regards to the domain of Fengshui or any of the five arts of Chinese knowledge. The former being the innate or essence (体); the latter being the application or function (用). This brings us to the very first important principle of the Early Heaven and Later Heaven Eight Trigrams.
(1) – Early Heaven as Essence; Later Heaven as Function
As mentioned, Early Heaven Eight Trigrams is the Essence whereas Later Heaven Eight Trigrams is the Function. Hence, anything that involves the structure, innate properties, model, etc., uses the Early Heaven Eight Trigrams, whereas anything that involves the usage, calculations, applications, directional, etc., uses the Later Heavy Eight Trigrams. One must bear in mind not to be confused with these two.
(2) – Different Position of Trigrams
Clearly, the Trigram position is different between Early Heaven and Later Heaven Eight Trigrams. For example, the position of Qian Trigram in Early Heaven Eight Trigrams is represented by Li Trigram in the Later Heaven Eight Trigrams; The position of Gen Trigram in Early Heaven Eight Trigrams is represented by Qian Trigram in the Later Heaven Eight Trigrams.
(3) – Association of Early and Later Heaven Eight Trigrams
As both Early Heaven and Later Heaven Eight Trigrams arises from the birth process of Tai Ji, Liang Yi and Si Xiang, hence those of similar Trigram (同卦) can be interconnected although the position of each Trigram differs between Early Heaven and Later Heaven Eight Trigrams. For example, Li Trigram of Later Heaven Eight Trigrams can be interconnected with Qian Trigram and Zhen Trigram of Later Heaven Eight Trigrams due to similar Qi, likewise for Kun Trigram of Later Heaven Eight Trigrams, it can be interconnected with Kan Trigram and Xun Trigram of Later Heaven Eight Trigrams.