Hun () and po () are types of souls in Chinese philosophy and traditional religion. Within this ancient soul dualism tradition, every living human has both a spiritual, ethereal, yang soul which leaves the body after death, and also a corporeal, substantive, yin soul which remains with the corpse of the deceased. Some controversy exists over the number of souls in a person; for instance, one of the traditions within Daoism proposes a soul structure of 三魂七魄; that is, "three and seven ". The historian Yü Ying-shih describes and as "two pivotal concepts that have been, and remain today, the key to understanding Chinese views of the human soul and the afterlife". The Chinese characters 魂 and 魄 for and typify the most common character classification of "radical-phonetic" or "phono-semantic" graphs, which combine a "radical" or "signific" (recurring graphic elements that roughly provide semantic information) with a "phonetic" (suggesting ancient pronunciation). (or 䰟) and have the "ghost radical" "ghost; devil" and phonetics of "cloud; cloudy" and "white; clear; pure". Besides the common meaning of "a soul", 魄 was a variant Chinese character for "a lunar phase" and "dregs". The Book of Documents used 魄 as a graphic variant for 霸 "dark aspect of the moon" – this character usually means 霸 "overlord; hegemon". For example, "On the third month, when (the growth phase, 生魄) of the moon began to wane, the duke of Chow [i.e., Duke of Zhou] commenced the foundations, and proceeded to build the new great city of Lǒ". The Zhuangzi "[Writings of] Master Zhuang" wrote 糟粕 (lit. "rotten dregs") "worthless; unwanted; waste matter" with a 魄 variant. A wheelwright sees Duke Huan of Qi with books by dead sages and says, "what you are reading there is nothing but the [糟魄] chaff and dregs of the men of old!". In the history of Chinese writing, characters for 魄/霸 "lunar brightness" appeared before those for 魂 "soul; spirit". The spiritual 魂 and 魄 "dual souls" are first recorded in Warring States period (475–221 BCE) seal script characters.