The Great Vacuity is clear. Being clear, it cannot be obstructed. Not being obstructed, it is therefore spirit. The opposite of clearness is turbidity. Turbidity leads to obstruction. And obstruction leads to physical form. When material force is clear, it penetrates; and when it is turbid, it obstructs. When clearness reaches its limit, there is spirit. When spirit concentrates, it penetrates like the breeze going through the holes (of musical instruments), producing tones and carrying them to great distances. This is the evidence of clearness. As if arriving at the destination without the necessity of going there, penetration reaches the highest degree.

(Chang Tsai)