Steve James wrote: The Chens did have some texts, too, but (iirc) Chen Xin's "Illustrated" does not mention "peng" at all, but focuses on "Chan ssu jin."
I don't remember if Chen Xin's book mentions peng or not, but it is central to Chen training.
My argument is only that the phrases that most people know when it comes to tcc come via scholarly practitioners of Yang influenced styles.
I think that is accurate.
So, we're forced to struggle with analogies.
I don't think we are forced to. I don't think we have to discuss peng at all. Folks might chose to, but don't have to. It is something that is felt and something that is developed. Talking about it, discussing it doesn't develop it. Training does.
Some of us remember the Peng Wars very well, and don't want to relive them.
Definitely don't want to re-live them.
But, here's the description of "peng" that appeared earliest in the Classics (afawk).
SONGS OF THE EIGHT POSTURES
Attributed to T'an Meng-hsien
as researched by Lee N. Scheele
The Song of Peng
What is the meaning of Peng energy?
It is like the water supporting a moving boat.
First sink the ch'i to the tan-t'ien,
then hold the head as if suspended from above.
The entire body is filled with springlike energy,
opening and closing in a very quick moment.
Even if the opponent uses a thousand pounds of force,
he can be uprooted and made to float without difficulty.
The interesting thing about that "song" is that people usually quote the first part of it: the "water supporting a boat" part, and its physical mechanics, qi to the dan tian, head suspended, filled with "spring-like energy". The first part attempts to describe what peng is (like) and how to physically manifest it.
The second part seems to be about how the body is used to uproot an opponent.
It isn't really very clear about what is the relationship, if any, between the first half of the song and the second half: the first is about how to "create" peng, the second is how the body is used to uproot an opponent. The reader is left to make a connection between sinking qi to the dan tian, suspending the head and the entire body being "filled with spring like energy". Chen Xiaowang, for example, defines peng as "qi flowing everywhere [in the body]".
What many seem to miss is the "spring-like energy" part of the song. What is the characteristic of a spring? That when a force is applied it compresses, it mechanically stores energy in proportion to the amount it is compressed; when the force applied is removed, it expands, releasing the stored force. (Note that water is considered incompressible and cannot be spring-like.) Thus, in use, in application, it is not a static situation. Instead, in use, it must compress and expand: "opening and closing in a very quick moment".
If viewed from the perspective of a clear, precise, technical, instructional description, it is pretty poorly written.
I'd recommend that students spend their time practicing under the direction of a good teacher, rather that spend much time on translations of Classics. The Classics are not a detailed instructional manual.