It is obvious that there is a lack of understanding on what is CBM and what is CBMP.
CBM. The shoulders rotate before the step is taken. That is CBM.
CBMP the shoulder is already in position, or it should be, when the step is taken, and is a foot position only. Is that too hard to comprehend.
Try the forth step of a Reverse Weave from a Promenade position in the Waltz. Is the shoulder in position. Is the step taken across the body in CBMP.
Let us not forget that the forth and the fifth step are taken by stepping back diagonal to the centre.
One of our leading lights writes. It is one thing to perform a group. But it is another to know exactly how it should be done.

"CBM. The shoulders rotate before the step is taken. That is CBM."

Not exactly. It may be a prominent feature of inline natural CBM, but it's a less accurate description of the mechanism of natural CBM done on top of CBMP. And it's very much contrary to the character of reverse turn CBM, where the rotation begins subtly in the lower body with the upper body rotation necessarily delayed until late in the step to keep from collapsing the topline.

"CBMP the shoulder is already in position, or it should be, when the step is taken, and is a foot position only."

By definition, CBMP is a foot position, NOT a body position. However CBMP does strongly imply some things about the body position, but what exactly those are depends to some degree on the capability of the dancer. For a relatively stiff dancer, a CBMP position may require the the entire torso already be turned strongly to the right, leaving comparatively little allowance for additional "CBM" rotation (though some is still all but certain to be present if a figure with actual turn is being commenced). But for a more flexible dancer, there's quite a range of body rotation possible within CBMP foot positions, and most will use this to advantage. Certainly it can be overdone, but a judicious use really contributes to the ease, flow, and appearance of the dance.

"Is that too hard to comprehend."

It's not a question of understanding what you are saying, but instead the simple fact that what you are saying is untrue.

"Try the forth step of a Reverse Weave from a Promenade position in the Waltz. Is the shoulder in position."

It may be in a sufficient position, but it's not in an ideal one. The figure will be a lot better with some additional body rotation to achieve a body position compatible with a more flowing progression in CBMP.

"One of our leading lights writes. It is one thing to perform a group. But it is another to know exactly how it should be done."

We might also say, it is one thing to read the book and accurately recall the FACTS of what is says. It's another to apply that to advantage in ones dancing.

You seem to have trouble with both acknowledging that the book lists slight CBM on the first step of the lock commenced outside partner in CBMP, and also with understanding that the execution of such cases, while involving less body rotation than the inline case, still ideally involves some.

(Posted in response to yet another message which then vanished)

"CBM must embrace the turning of both
hip and shoulder."

Both are often involved, and in more pronounced cases will act largely together, but it is not an actual requirement that both undergo rotation by the same amount at the exact same time. Figures transitioning between closed and outside partner or promenade, as well as reverse actions in general, all see some degree of difference in the rotational use of shoulders and hips.

"There is nothing which says that the lower body and the upper body turn at different times."

While this is a detail of technique only touched on in the traditional books, it is a reality of execution that will come up if you take the time to study in depth with truly expert teachers.

"Page 15 16 Paragraghs 1 to 4. Plus below. Care must be taken not to turn the shoulders independently otherwise a ugly dipping movement will result."

If we consider the faults students tend to make, this is reasonable initial advice: students tend to try to use activity in their shoulders to initiate turns, and are reluctant to use their hips. In general, they must learn that their arms and even shoulders are not handles for turning their body.

But in the case of reverse turns, we need to not only remember to use the hips as much as the shoulders - we must actually learn to begin the rotation in the legs and hips before we rotate our shoulders, because maintaining an offset hold in a reverse turn requires that the topline rotate much later than it would in a natural one. In effect, this is taking the warning not to turn the shoulders without the hips even further - a case where the hips need to begin to turn before the shoulders.

Schedule some lessons with leading competitive coaches and ask about the mechanics of reverse turn CBM - you'll find there's a bit more to the story than is obvious from an initial reading of the book.

"The fifth step also is back diagonal to the cenre, that one is in CBM."

There is no such thing as a step "in CBM". Steps may be taken "with" CBM, but no step is ever "in" it.

"That there is "CBM" on step one of the outside partner lockstep is an indisputable fact of definition."

Not quite.

There are (at least) three 'definitions' to choose from for the initial step (man RF OP):

1) ISTD as step 5 of progressive chasse - CBM

2) ISTD as step 1 of lock step - slight CBM

3) IDTA (Guy Howard) as step 1 of lock step - no CBM

Note Guy Howard does not use the overlapping step 5 of chasse = step 1 of lock, so there is no conflict there.

None of this affects what is seen on the dance floor though and is probably only relevant when taking professional exams.

"1) ISTD as step 5 of progressive chasse - CBM"

This is not the first step of a lockstep, its the first step after a progressive chasse. If a lockstep is danced there, and details are given for an outside partner lockstep, then those are what apply rather than the generic description tagged onto the end of the chasse.

"2) ISTD as step 1 of lock step - slight CBM"

This is what applies

"3) IDTA (Guy Howard) as step 1 of lock step - no CBM"

It would be informative to note that Howard does not apply CBM even when dancing the lock inline after a natural turn.

This should make it evident that Howard is writing in a different language having a different definition of CBM and its application. The Howard/IDTA definition begins by stating that CBM is used to commence turn (which would not apply in these cases). The Moore/IDTA definition of CBM states the mechanical aspect first and appends the frequent (but not universal) association with initiating turn as an afterthought.

In each "language" the places where CBM is and is not used are ultimately part of the "definition" of CBM in that language.

As we've both acknowledged, the application of CBM in the body while dancing is a different subject than it's official definition.

Anonymous. Are you making this up as you go along. If the first step of a Lockstep is not a Heel Lead outside partner on the mans RF foot then what is it.
And as far as doing a Natural Turn in the Quickstep. Nobody does a Natural Turn once they have passed their Bronze Medal. The same goes with the Natural Turn in the Waltz. I can not remember ever seeing a Natural in the Quickstep in any demonstration or competition that I have ever seen.
Taking your own words on the Lockstep . This is not the first step of a Lockstep. Its the first step after a Progressive Chasse. Surely you should say its the last step of a Progressive Chasse otherwise you are saying it is the first step of the Lockstep.

"And as far as doing a Natural Turn in the Quickstep. Nobody does a Natural Turn once they have passed their Bronze Medal. The same goes with the Natural Turn in the Waltz. I can not remember ever seeing a Natural in the Quickstep in any demonstration or competition that I have ever seen."

Meanwhile, in the real world, 1-3 of the natural turn remains a quite popular figure in both dances.