 The identification of the yin-yang principle with the hun and po souls evidently occurred in the late fourth and early third centuries BCE (Yü 1987:374) , and by "the second century at the latest, the Chinese dualistic conception of soul had reached its definitive formulation."
<clarity>  The identification of the yin-yang principle with the hun and po souls evidently occurred in the late fourth and early third centuries BCE (Yü 1987:374) , and by "the second century at the latest, the Chinese dualistic conception of soul had reached its definitive formulation."
 The identification of the yin-yang principle with the hun and po souls evidently occurred in the late fourth and early third centuries BCE , and by "the second century at the latest, the Chinese dualistic conception of soul had reached its definitive formulation."