Greetings Dan,
I am not sure we actually differ on much except for some nuances of terminology and perhaps some aspects of our theoretical frameworks.
I am unsure whether my teacher or the classics hold the eight energies to be comprehensive or not; however, my impression is that they do not. I don't have any particular objection if you hold that view and even see how it could have some advantages.
I should first clarify that I frequently dislike talking too much about "energies' in the plural, because it tempts me to envision mysterious "qi emanations" and make things more complicated than they perhaps need to be. I have probably learned more Chinese and read more traditional Chinese philosopher than the average Tai Chi enthusiast outside China, but my fundamental understanding about how the world works is still grounded in modern science and not in emanations of qi.
The classics taught about eight energies and assign them to the eight trigrams. I understand this as an implicit claim to an exhaustive classification that covers the totality of Tai Chi energy. Nevertheless, the writings of the various families talk a lot about other "energies" and don't seem too bothered about describing them as sub-classifications of the other eight. Even the classifications differ in detail and so don't seem to give me any practical guidance.
One Tai Chi saying goes very roughly like: "Hold the eight trigrams in the arm; tread out the five phases/behaviors in the feet; and focus on the Taiji in your mind." For me, this means focusing the framework of the eight "energies" on arm and hand movement.
One of my teachers talks about using energy to deal with energy. I take this as my starting point. I understand it to mean that I want to join my energy with my opponent's through the contact point to make one
Taiji. I control the development of that Taiji by moving second, but the key dynamic of the change can center either on me or my opponent and be offensive or defensive. Once the opponent's is controlled, it is then safe and advantageous to emit energy into them using strikes, kicks, grabs, take-downs, or locks. These are what I called "icing" in my previous post.
That same teacher, when talking about strategy, has often alluded to Sunzi's theories; and I take that as my end point. The semi historical Sunzi/Sun-Tzu prized flexibility and the dynamic of combination over a fixed repertoire of tactics and the prowess of individual soldiers. I thus try to set the goal of my practice on being able flexibly to combine energy to my advantage rather than on strengthening any particular repertoire of techniques.
As an overarching framework, my teacher has also frequently talked about the progression from 着习 (familiarity with movements), 懂劲 (understanding of energy), and 神明 (miraculous clarity/omniscience). I take the classification of the eight energies to be important to the first two steps, but not the last one.
As I have been taught, I begin with a largely choreographed application of each of the eight energies. One each is the minimum. One closed-position application and one open-position application is better. And three or more variations is excellent.
Although one energy is prominent, we make no bones about almost using them in combination. We assume that two contact points are generally required to have good control and so generally apply at least two instances of energy during an application. Even more is quite usual.
The applications force you to take a yang strategy, since you have to initiate them starting from our vertical circle and not simply wait for the opponent to give you the opportunity. We also have to respect the maximum of "moving second," and so the application forces you to learn how to lead the opponent to give you the energy you need to proceed, starting from our vertical circle and then transitioning to other circles or other adjustments as necessary.
Just working externally, you can make all the applications work after a fashion; and so I try to focus more on internal aspects as I move to the phase of "understanding energy." I try to examine what about the waist movement, timing, direction, changes in pressure, contact points, etc. leads the opponent to tend to do what you want. "Give up yourself and follow the other," even though you are starting from a leading position and are therefore yang in terms of aggressiveness.
For Ward off/Peng, I understand the quality you want the opponent to feel is that of rising energy, such as being buoyed up out of their root. In our standard application, to me this means focusing the energy into the opponent's shoulder in one of two ways so that their heels want to come up. The helping hand can use a variety of techniques to fix the second contact point.
For Rollback/Lu, I understand that the quality should be one of stroking out the opponent's energy, like stroking a beard into a point. In our standard application, one of the things I focus on is which arm needs to lead the opponent into position. You need to follow the opponent to understand which is most appropriate.
I know that some practitioners define Rollback as a diverting energy, for instance in their horizontal circle. Our horizontal circle is performed in a very large fashion. With a circle of this size, merely turning the waist is insufficient to deal with the opponent's energy without doing more. I sometimes try to demonstrate this by having students push on a Pilates ball I hold in front of me and try to use to turn their push aside. In this scenario, the opponent will still feel as if you are resisting the forward movement of their energy. I therefore focus on a different set of feelings to define Rollback.
For Press/Ji, I understand that the desired quality is crowding out the opponent's energy. "Squeeze" is probably a clearer translation of Ji3
挤 One way I sometimes demonstrate the quality is by performing our horizontal circle with my back against a wall. Because of the size of our circle, I find it extremely difficult to continue the circle with Rollback if I have no ability to retreat. Instead, I can use Press in a defensive fashion, to squeeze the opponent's energy over to the other side and change into what we call the Four Energy Circle.
For Push/An, I focus on a quality of "pressing on the combined energy." I find the traditional translation of An
按 as push to be very awkward, since many uses of this energy are not pushes. One frequent use is to control an oncoming punch by pressing lightly on the opponent's wrist and guiding it to the side. You cannot use "push" to mean this in English.
For Pluck/Cai, I think that "pluck" is a good description. As one of the "diagonal energies," the idea is to use a somewhat cruder from of energy manipulation if the first four more subtle, but straightforward techniques are insufficient.
The force of our grabbing technique is not at all gentle. This means that when you apply it, you not only give your opponent a clear point to attack, but also tend to provoke a counter reaction. This means that when you apply Pluck, you have to do more than just grab away and actually complete much of your control of the energy before actually letting your opponent feel the grab.
For Split/Lie, I am currently settling on "snapping torque" as the general idea. The torque can be in your body or the opponent's body, but the energy must snap in some way. A major use of this tactic is to twist out of a disadvantageous position to an advantageous one. Since the motion tends to involve some kind of urgent gyration, it is again cruder in application than the four "straight" energies.
For Elbow/Zhou, the idea is to use "elbowing" to control the energy flow when the fingers, hands, and forearms can no longer serve. As with the other energies, a focus of energy is described, but not necessarily any specific contact point. The opponent perceives the energy as focused on your elbow, but may be in contact with some other part of your body. On our standard application, the contact is actually with the upper arm.
For Shoulder Stroke/Kao, the idea is to use the vertical approach of the body to control the energy. This basically means anywhere from hip to shoulder.
After practicing these, we then practice at least one counter for each of the applications. More is better. This practices the Yin side of the strategy and begins to involve other aspects of energy exchange, such as changing the flow of full and empty to your advantage or trying to use your contact point to manipulate your opponent's ability to sink qi appropriately. If the opponent cannot sink their qi, they cannot power their techniques.
Once you gain proficiency in these and then combine them with moving step practice, you can best practice the variety of scenarios represented in the form in all their variations. At this point, you will have learned to emit energy proficiently and then can do so with any part of your body.
I would say that my training has not focused much at all on striking or kicking and yet I could say that I have trained or been shown ways to strike or emit energy from than two dozen places on the body. The focus has always been on learning better how to Fajin, rather than on the specifics of the particular strike. For example, I know about storing energy in general, but not how to "chamber" a Tai Chi punch.
As an example of this framework, I might discuss the energy involved in Chop with Fist in the Form as follows. After Fan through the Back, your right rear might be exposed to a strike. To deal with this, you pivot your body and drop your right elbow and palm to use Zhou/Elbowing or An/Push to control the energy of an oncoming punch and raise your left arm in Peng/Ward Off to guard your head. Then you drop your left arm and palm into An/Push or Pluck/Cai to free your right arm to circle into a backfist or finger slap.
I have run out of time for now and hope this helps.
Take care,
Audi