It comes out from no source, it goes back in through no aperture. It has reality yet no place where it resides; it has duration yet no beginning or end. Something emerges, though through no aperture - this refers to the fact that it has reality. It has reality yet there is no place where it resides - this refers to the dimension of space. It has duration but no beginning or end - this refers to the dimension of time. There is life, there is death, there is a coming out, there is a going back in - yet in the coming out and going back its form is never seen. This is called the Heavenly Gate. The Heavenly Gate is nonbeing. The ten thousand things come forth from nonbeing. Being cannot create being out of being; inevitably it must come forth from nonbeing. Nonbeing is absolute nonbeing, and it is here that the sage hides himself.
Zhuangzi, The Complete Works of Chuang Tzu
being, death, existence, heaven, life, life-and-death, nonbeing, nonexistence, reality, source, tao, taoism, yang-and-yin, yin-and-yang