[cypressperch]

is simply a shoulder turning and unturning, a hip turning and unturning, and an arm swing that moves up and down. Two turns and a swish as Mr. Jacobs has said. If the golfer stays connected, big muscles can be the engine at the center of the swing regardless of plane. But even if you are concentrating on the big muscles, there is still an arm-swing going on so that really they are not just along for the ride even if that is not what you are focused on.

Some so called one-planners have their hands so high at the top of their back-swing that it seems impossible to me that there was no shifting to a different plane going back.

I also think that when a person finds that using the principles of Hardy's one plane swing results in pushes, shanks, and other problems that they will eventually avoid getting the club so far behind them. There swing will have become too round. They will find better contact when they keep the club more in front. Likewise, the person who tries to approach the ball early and keep the club head square too long on the target line will have too straight or squared a clubhead path, and will probably slice a lot. This person will end up getting the club coming inside earlier going back to allow an attack from the inside coming back to the ball. They will be moving in the direction of a one-plane swing.

So many variables (posture, physical build, rhythm, tempo, strength, equipment, lie angles, shafts, etc, etc) come to play in developing one's swing that it is hard to avoid the game's complexity. About the best thing you can do is find a good treatment of the fundamentals (Hogan, Jacobs, etc), hopefully get some good professional instruction, get some equipment that fits, and then go start with the digging that is required to become a good golfer. And it may be that Hardy can be an adequate guide. Time will only tell if Hardy will stand the test of time. He may have clarified things for some, but I am certain that he has confused a good many as well.

Sincerely, Cypressperch