You wrote: “There is something mutually contradictory about all of these explanations. It strikes me that they are all winging it and that chousi is not a particularly important concept in Yang style.:
While I can agree with your observation that the various explanations of “yun jin ru chousi” are not all alike, I have to respectfully disagree with your conclusion that it is not an important concept in the Yang style. A few days ago you asserted a similar distain for the chousi concept, “Especially since the Yangs never mention it.” Now that we know that Yang Chengfu and Yang Zhenduo both did mention it, we’re advised to discount the concept as unimportant because they apparently didn’t know what they were explaining very well; they were “winging it.”
Metaphors seldom have pat explanations that one can take literally. If they did, people wouldn’t use metaphors; they would just use the pat explanations. People usually use metaphors because they capture a meaning or a nexus of meanings, but do so in a way that can’t be captured in a more straitforward expression. David Nivison wrote, “Students of Chinese philosophy have usually seen their subjects as a succession of people who lived, acted, taught and died, rather than a weaving of strands, any one of which may be a subtle dialectic of question and answer.” Well, he’s got my attention. Apparently there’s a better way to view the subject. I’m sure it doesn’t have to do with weaving, or with strands, but I follow what he’s getting at, and I want to know more. Zhuangzi wrote a story about a guy butchering an ox. It’s not something I imagine I would particularly enjoy watching, but Zhuangzi makes it seem like poetry in motion, and it’s just packed with metaphors on how to “cultivate life” on every level from the mundane to the sublime. Unpacking the metaphors could probably be done in a lot of divergent ways that may or may not help one do one's laundry or go grocery shopping, but none of the unpacking would do the job as well as just reading and pondering the story.
So it may be that the chousi metaphor is not particularly compelling to you, which is fine. But I imagine if it weren’t an important Yang concept, the Yang’s really wouldn’t have mentioned it.