It is unseen because it is colorless; it is unheard because it is soundless; when seeking to grasp it, it eludes one, because it is incorporeal.
Because of these qualities it cannot be examined, and yet they form an essential unity. Superficially it appears abstruse, but in its depths it is not obscure. It has been nameless forever! It appears and then disappears. It is what is known as the form of the formless, the image of the imageless. It is called the transcendental, its face (or destiny) cannot be seen in front, or its back (or origin) behind.
But by holding fast to the Tao of the ancients, the wise man may understand the present, because he knows the origin of the past. This is the clue to the Tao.