"Shi Shen (识神): This is the post-heaven Shen. It's our daily mind. The Shi Shen loves movement. It loves stimulation. Most of all it loves your attention. Maybe it's our inner toddler. The Shi Shen is an ego maniac. It wants to trick you into believing you're it.
Yuan Shen (元神): This is the pre-heaven Shen or original Shen. The Yuan Shen loves stillness. Generally speaking, the Yuan Shen won't wake until death or near death. But if you can completely calm the Shi Shen, the Yuan Shen will begin to stir. And so the Sage hacks the system and dies before dying.
Yin Shen (阴神): Much like the Shi Shen, it is associated with Po and so associated with emotions and ultimately ego. Po, corporeal spirit of the Lung network, governs Qi. A Yin Shen practice, therefore, develops the ability of the mind, Shi Shen, to control Qi. The practices can be very powerful but they never eliminate the Shi Shen. Developing Po is like acquiring material wealth, you don't take it with you.
Yang Shen (阳神): Yang Shen is associated with Hun. Hun is said to be our immortal aspect. Yang Shen practice is also called Three Immortals practice in the Ling Bao Bi Fa. Wei Bo Yang outlines two methods for achieving Yang Shen, the Greater Virtue path and the Lesser Virtue path. The Greater Virtue path is accomplished through the elimination of desires. Desireless the Jing to Qi to Shen to Xu process happens quickly and automatically.
The Lesser Virtue path involves the step by step process of creating the Lower Dan Tian and undergoing the arduous alchemical process. Neither path is better or worse, nor are they mutually exclusive. Generally speaking, many start on the Lesser Virtue path to strengthen the body, the Jing, and the Will for the obvious reason that without these basic requirements, it's nearly impossible to attain the state of genuine, unattached stillness."
written by a friend, SYD