Tao Te Ching Chapter 14
Looked at, but cannot be seen -
That is called the Invisible (yi).
Listened to, but cannot be heard -
That is called the Inaudible (hsi).
Grasped at, but cannot be touched -
That is called the Intangible (wei).
These three elude our inquiries
And hence blend and become One.
Not by its rising, is there light,
Nor by its sinking, is there darkness.
It cannot be defined,
And reverts again to the realm of nothingness.
That is why it is called the Form of the Formless,
The Image of Nothingness.
That is why it is calledthe Elusive:
Meet it and you do not see its face;
Follow it and you do not see its back.