In Ba Gua, Xing Yi and Tai Ji we start in a posture referred to as the Wu Ji posture. Below is picture of Sun Lu Tang in the Wu Ji posture.
Wu Ji (无极) mean something like ultimate emptiness (wu is nothing/emptiness and ji mean extreme/ultimate). In Chinese cosmology ultimate emptiness /wu ji) gives birth to ultimate fullness (Tai ji, 太极, same characters that are used för Taiji Quan). Ultimate fullness splits into yin and yang. After that there are different ways to describe what happens. In Xing Yi the next progression follows the description of Dao De Jing i.e. yin and yang (Liang Yi) gives birth to San Cai (three capabilities, 三才) and from San Cai, the 10.000 things (wan wu) is created. San Cai is represented in San Ti Shi which is why we in Xing Yi move from Wu Ji posture to Tai Ji posture and then to San Ti prior to any other movement (e.g. one of the five elements fists or one of the 12 animals). In Ba Gua Quan, the progression instead follows the description from the book of changes (Yi Jing) i.e. from two appearances (Liang Yi, 两仪) the four forms (Si Xiang, 四象) are born. The four forms gives birth to Eight Trigrams (Ba Gua 八卦) which where the name of the art of Ba Gua Quan comes from. The eight trigrams in turn gives birth to the 64 heagrams that are described in the book of changes and so on.
So, what does this have to do with the posture called Wu Ji posture?
Lets look at it from the perspective of the art of Ba Gua Quan. The study of Ba Gua is fundamentally the study of change. There are different types of change. There is combinatorics and permutations but also spontaneous creation.
Combinatorics is the the kind of creation that occurs when we mix two or more different things and thus creating something new. Without the ability to do this, we would have to have examples of every possible movement in the forms that we practice, otherwise we would not be able to use it. This also leads to plenty of vulnerabilities where, if you knew the movements of a style, you could easily counter it but inventing a movement that could not be defended against . Obviously this would lead to very week martial art where you would have to make sure nobody from the outside saw what you practiced etc. This is also the reason why Sun Lu Tang did not create a fixed form for the 64 hands but instead focused on teaching students how to create these themselves based on the 10 basic forms.
Permutations is the study of how things evolve from a certain point. For example if I have a movement where the palm is facing upwards, the permutations of that would be palm facing downwards, to the inside and to the outside. A common saying is Ba Gua Quan is “one hand separates into 8 forms of usage” which is just this idea.
Combinatorics and permutations are ways to create something out of something else. However, to be able to manifest spontaneous creation we need to free action from habitual patterns. In this sense, creating something through permutations and combinations “masks” or “hides” real creativity. It is not that permutations (yin yang giving birth to 4 power, 4 powers giving birth to eight trigrams, eight trigrams giving birth to 64 hexagrams etc.) is “bad” – it is on the contrary something vitally important. But to cultivate the ability to truly spontaneously create we need to go back to the original emptiness i.e. wu ji.
Abiding in wu ji is the cessation of thought, form, time etc. (ultimately even awareness itself) so in that sense true wu ji is not something that can be experienced and yet we can “touch” it. When we do, something transforms. It is difficult to explain in detail but you will find that when practicing the swimming body palm (a.k.a changing palms) something now flows from this nothingness which is truly creative.
Meditation practice makes it easier to approach this. As always, it starts from entering stillness (ru jing 入静). From there you continue to let go of thoughts, feelings, time and space etc. until only awareness remains, and letting go of that you touch the non-beingness of Wu Ji. Once you have done this you can let the posture of Wu Ji be a representation of this so that every time you take that position you reconnect (if ever so lightly) to this ultimate emptiness. I realize that describing like this makes it sound like a something “technical” or something that can be cause by a series of actions. This is not really the case. Ultimate emptiness has no cause. Since it has no cause, whatever comes out of it has no cause either i.e. it is completely spontaneous and always new.
Then you reconnect with combinatorics and permutations of the “true forms” (i.e. the single palm change, double palm change etc.) and the result is swimming body linked changing palms (游身八卦连环掌).
It is important to “solidify” this connection. The first step is of course to practice swimming body palm while paying attention to not repeating patterns and not just limiting the practice to combinatorics and permutations. Then we need to make sure everything does not fall apart under pressure which is why practicing sparring and free fighting is vitally important for a real martial art.
Now, there is the “ideal” and there is the practice. Practice will always be an approximation. So we stand in Wu Ji posture which is like a kind of “ritual” or “symbolic representation” of the real wu ji and we let go of thoughts, expectations etc. and thus touch (even if it is ever so lightly) the realm of emptiness so that our practice may flow fresh from the source and is not just a repetition of movements but a live expression of the very truth of our being.