Lao-tzu said:
The Way can be used for weakness or for strength, for flexibility or for firmness, for passivity or for activity, for darkness or for light. It can be used to embrace heaven and earth, it can be used to respond to the times without fixed convention.
Knowing it is shallow, not knowing it is deep. Knowing it is external, not knowing it is internal. Knowing it is coarse, not knowing it is fine. Knowing it is not knowing, not knowing it is not knowing it. Who knows that knowing is not knowing and not knowing is knowing?
The Way cannot be heard; what is heard is not it. The Way cannot be seen; what is seen is not it. The Way cannot be spoken; what is spoken is not it. Who knows that its form is not form? Therefore when everyone knows that good is good, this is not good. Those who know do not say, those who say do not know.
Translated by Thomas Cleary