Citation? As in my response above I'll look one up for you and post it.
Secondly if you read my response earlier you will see my explanation. How can ground force be 'centred' someplace other than the ground? Well that's for you to discover. The practice and use of Koshi answers that.
Yes it is another kind of force and that's the whole point. For me put in simple terms it is the Earth energy, Ki. Ground force is not and never has been my terminology. Thus I have no use for it or need for such terminology.
I've had several teachers who were well-versed in Tohei's methods and had direct experience with him as students, each of whom continued to use his four principles, his teachings on ki, his methods of ki breathing, and so forth, even after the great split, when they no longer had any formal affiliation with him. Subsequently, in my own training, I've investigated those methods in some depth over a number of years to good effect. Don't get me wrong, it can be great stuff.
I've also done some study of the Japanese view of mind and body, and its transmission to the west -- though my scholarship and my practical application are woefully lacking when I compare my efforts with others of real accomplishment. I think it is fair to say that Tohei was the first person to transmit these teachings to the west in the language of Dale Carnegie's "How to Make Friends and Influence People," (which was apparently one of Tohei Sensei's favorite English-language books). But the distinctive differences between the Cartesian dualism of body and mind and the pan-Asian (it's really not just Japanese, you see) view of the interdependence of body and mind were addressed in both terms of both mental understanding and physical practices by a great many people before Tohei, some Japanese, some Chinese, some Indian, and even some in the West.
In your original post, you state quite unequivocally: "Thus the centre of so called 'ground force' in Aikido terms or Japanese is Koshi.
In this post, you state quite unequivocally: "Ground force is not and never has been my terminology. Thus I have no use for it or need for such terminology."
Mike Sigman has remarked a number of times over the years on the phenomenon of folks who say "yes, we have that," or "yes, we do that."
Well, I could say "Yes, before I encountered Mike, I was doing that all along."
To go back to one of the electrical examples he likes so much, my statement that "I was doing that all along," would have been entirely accurate if I meant that "Before I met a guy who knew how to put together a radio receiver, I was once reading largely theoretical works about radio waves and circuit design and getting some general grasp while he was listening to Vivaldi on the radio receiver he built from scratch."
I'm not disputing the importance of the hara, or koshi, or any one of a number of points you make. I'm also not claiming any major achievement in my ability to manifest "ground force." But I am claiming some small familiarity with aikido in general, the force generated by senior practitioners, and the methods used to train that force on the one hand, and on the other hand, with the kind of force Mike can generate, and the basic methods he uses to give folks the proverbial "foot in the door." I have met senior aikido practitioners who can generate tremendous force. But the precision of training method is something else entirely.
If "ground force" isn't part of your terminology, how can you know that you are generating it? If you can't know that you are generating it, how can you assert that it is the same as what you think you know? And if you have no need of it, but it's the same as what you have, aren't you saying that you don't need what you do have?
In short, it's difficult to make heads or tails out of what you're claiming here, and I don't think the confusion is all mine.