"......TaiJi is like a great river, rolling on unceasingly.....""...suddenly appear....suddenly disappear..."
These lines from the Classics are wonderful practice guides. Perhaps they represent a paradox, of "ongoingness" and at the same time, differentiation. Is this "seeking stillness in motion, and motion in stillness?" Perhaps the key is in the yin-yang nature of inter-producing, inter-consuming, and inter-dependent. Let's consider "suddenly appear" as yang (active, full) and "suddenly disappear "as yin (calm, tranquil, empty).
When the full has filled, empty it!
When the empty has emptied, fill it!
This exchange of full for empty and empty for full is an experience of yin and yang within us. Just as our lungs empty and fill, our legs (and corresponding upper body) do so as we move through the form.
This idea of filling and emptying is one possible interpretation of "suddenly appear, suddenly disappear." Actually the Chinese characters provide a deeper insight. More literally, the characters represent the idea of suddenly becoming manifest, present, to be revealed, and suddenly becoming concealed, hidden. This also is a yin-yang relationship.
No matter how one interprets these lines, it is essential to realize that appearing and disappearing is happening simultaneously, and cannot be separated, as is true with all yin-yang relationships.
As we practice "rolling on unceasingly," simultaneously appearing and disappearing (differentiating), we find the thread that flows through all of the movements, the breath. The qualities of the breath are said to be "long, slow, fine, quiet and continuous". Each breath has continuity, the end of inspiration becoming the beginning of expiration, with no breaks or holds. The breath flows unceasingly, as does the body. Remember to breathe, in a relaxed, quiet, calm manner, and allow the relaxed body to flow with the breath. As we move, fill the empty (suddenly appear) and empty the full (suddenly disappear), continuously and simultaneously, so that each movement has completion and continuity with the next. In this manner, the form is the TaiJi, flowing like a river, rolling on, unceasingly.