Chapitre 50: 050 Tang Jing

Whether it's the Yang Spirit or the Yin Soul, both are composed of the Primordial Spirit and the Primordial Soul; the only difference is that in the Yang Spirit, the Primordial Soul is in the soul while the Primordial Spirit remains in the physical body—that's what's commonly referred to as essence, energy, and spirit. Therefore, once a person dies, their essence, energy, and spirit dissipate, and their Primordial Spirit and its Yang Spirit can no longer be restored to life;

The Primordial Soul and Primordial Spirit of the Yin Soul are both in the soul, so even if the Yin Soul has dispersed, as long as one can summon back all of the Primordial Soul and Primordial Spirit, the Yin Soul will be revived. This is also why human beings cannot be brought back to life, but can go through reincarnation.