(OK I just worked out how to quote)
By coincidence, on a television programme tonight discussing the sense of balance, the presenter did exactly that whilst walking along a narrow beam. Not having a dancer's flexibilty or awareness of CBMP, as the right foot went forward so did the right hip and with it the right side.



It depends which definition you use. The ISTD one adds a subtle clue "... to maintain body line." I prefer the more definite IDTA version from Guy Howard's book which also appears in Alex Moore, which adds "... giving the appearance of CBM having been used but without turning the body."

Regards,
Howard

I didn't want to get too down and dirty with the details, since my goal was to make it easier for tangodancer or other newcomers to understand. But for the sake of discussion I'll explain.

The reason you can step straight into CBMP without rotating is because it is measured with respect to the direction you are moving. For example, if you face LOD and step towards DW with your left foot, you might at first assume that your shoulders are square and therefore you are not in CBMP. But with respect to the direction you just traveled -- diagonal wall -- your right side is very much in advance of the left side. So without having rotated at all, you have one side in advance of the other.

This is even true of a step taken forward in CBMP. The effect is more subtle, but it still applies. Your feet have two individual tracks, and when each moves along its own track, the movement is aligned squarely with the body. When one foot moves along the track of the other foot, ("forward in CBMP"), your direction of movement is no longer straight forward in line with your body's orientation, but rather just slightly offset. It may only be 5 degrees off (as opposed to the 45 degrees I gave the the example above), but that's still 5 degrees of CBMP. So even just stepping in line with yourself, as you would on a tightrope, puts you in a position of having one side of the body slightly in advance of the other with respect to the direction of movement, and again, without any rotation necessary.

Now so far I've been operating under the assumption that the feet and body are always oriented to the same direction. And of course, we all know that they can, and often should, turn at different times and to different alignments. One might then ask, "If I turn my feet to the direction of travel, but not the body [or vice-versa], am I still in CBMP?". Remember that CBMP is ultimately a position of the feet, so if you turn them exactly to the direction of travel, one is no longer along or across the track of the other. So even with your upper body offset, you are still not in CBMP. Here is where most beginners would be confused, because they tend to think in terms of sides of the body, not positions of the feet.

Still, though, it's a moot point because you would never try to achieve such a position. There's no good reason to do so. In the ballroom context, having your feet offset from the body is useful primarily for promenade and O.P. positions, where you step along (OP) or across (PP) your track anyway, and to do otherwise is to step into your partner's space. In O.P. position, for example, you step forward in CBMP. So the direction of travel is maybe a few degrees off from the alignment of the feet. This puts one foot along the track of the other, allowing you to step forward into the narrow space afforded by the O.P. position.

I hope this makes sense. To those who don't quite get it, don't worry. As I said before, it is easiest just to think of CBMP as a position of the feet. Trust that the sides of the body will take care of themselves (unless the step calls for CBM, but that's a different story).

Regards,
Jonathan

As I explained, if you are stepping in line with yourself, the side in advance is necessarily opposite the leading foot. You can't step in line with yourself and have the same side forward to the direction, or even be square to the direction for that matter. At least, not unless you have the feet and body turned to different alignments.

But as I said, whether you consider such a position CBMP or not is irrelevant, because it's a position you never take in ballroom. All steps taken with a right- or left-side lead are taken with feet on individual tracks; There's no reason to step along your own track when taking a side-leading step. And when you are O.P. or P.P., you would have to literally turn away from your partner to achieve such a position.

Ballroom technique is such that the feet should always be in parallel with each other and in-line with the body during forward and back steps, except when the position requires otherwise (O.P. and P.P. as the best examples). Since the example you describe is incompatible with these positions, it isn't relevant to ballroom movement.

However, just for the sake of argument: Regardless of it's relevance, what would you call such a position? Well, according to it's definition it is indeed called CBMP, because the definition refers only to the position of the feet. It makes no mention of the body because it is assumed that you are automatically in opposition, as per reasons I mentioned before. Nonetheless, the position in question does fit the book definition to the letter, so in that regard it's CBMP.

On the other hand, one often thinks of CBMP as an oppositional position. One also tends to think of CBMP and side-leading positions as being mutually exclusive opposites. So in that regard, you could argue that the position is not CBMP.

Either way, it's all theoretical, and certainly something I wouldn't bother to discuss with a student.

Regards,
Jonathan