My sense of yang and yin has been changing ever since I began studying with Bruce decades ago. It continues to change and evolve to this day. Somewhere in that span of time, I moved from a physical interpretation of chi and yin and yang to an understanding of the tai chi space and how yang and yin come out of and return to the tai chi space.
At first I only found the expansion. Then I started to notice the equal and opposite side of the expansion. Then I started to understand yin as “letting it all in”. More recently I’ve started to find a more “active” side of yin. Letting it all in is more passive.
I’ve recently started to find a pulling in. The energy that has expanded feels like it can be actively pulled into the tai chi space. This isn’t a contraction of muscle and tissue. And, it is distinctly different than letting it all in.
Interestingly, I immediately start to find the opposite side of this pull – the equal and opposite reaction that juxtaposes the movement pulling in with an outward expansion. This is where it gets a little strange, a bit confusing, and even arbitrary, to discuss the two sides of yin and yang.
So, how do you use this? You could use the pull to pull into the central channel when you are closing in the single palm change. Or you could pull into the upper and middle tan tiens at the beginning of the thunder palm movement. I find that a contrast between yang and yin helps. For example in the fire palm, you could be expanding from the upper and lower tan tiens while pulling into the middle tan tien.
Who knows? Anyway, as long as you are messing with the tai chi space, you’ll be on the right track.