Chapter 13
Look for it and it cannot be seen - this is called 'invisible.' Listen for it and it cannot be heard - this is called 'inaudible.' Grasp for it and it cannot be caught - this is called 'subtle.'
These three cannot be fully investigated, therefore they merge and become one.
Its upper aspect is not bright; its lower aspect is not dark.
Continuous and unceasing, it cannot be named; it returns again to the state of no-thing.
This is called the form of the formless, the image of no-thing; this is called the trance-like and indistinct.
Approach it and you cannot see its head; follow it and you cannot see its rear.
Hold to the ancient Way to master the present's manifestations.
To be able to know the ancient beginning - this is called the thread of the Dao.