Lao-tzu said:
The greatest simplicity is formless, the greatest Way is measureless. Thus the sky is round without being set to a compass, the earth is square without being set to a ruler. The word universe refers to time and space; the Way is therein, but no one knows its location.
So if people's vision does not see far, you cannot talk to them about something of immense scope; if people's knowledge is not broad, you cannot speak to them about what is finally ultimate.
Those who are imbued with the Way and commune with all beings have no way to deny each other. That is why the laws of enlightened leaders of ancient times were different in their measures yet were at one with each other insofar as they won the hearts of the people.
Now if are talking about the compass, ruler, square, and plum line, they are the tools of a skill and not the reason for its being a skill. That is why the greatest harpist cannot play a complete tune with missing strings, and a single string cannot induce melancholy alone. So stringed instruments are tools for producing a feeling of sadness, and not the reason for its being sadness.
When it comes to the spirit peacefully roaming between the hearts and the hands, freeing the mind to depict the spirit, giving voice to its modulations in the notes of the strings, that is something a father cannot teach his children, and children cannot learn from their father. This is a principle that is not transmitted.
Therefore calm is the ruler of form, and silence is the ruler of sound.
Translated by Thomas Cleary