We have to emphasize that Heng Tao is both ever-changing and unchanging; it is dynamic with an unchanging principle. It is the nature of reality as a whole. A reality must transcend any dualistic view.
The concept is very important, but is difficult to express with our ordinary language, in Chinese and any other language. We have to overcome this formidable obstacle in our discussion, to comprehend the logic structure of Lao-tzu.