Since i couldnt sleep, i decided to break the tape down and make some notes to post. Remember, these are Jim Hardy's statements not mine, so you really dont need to post to tell me this isnt right, or thats not how it works, just take it and think about it, i think he's dead on the money.
2 plane definition- Shoulder plane and arm plane, shoulders working more LEVEL , arms working on a different plane up and down. The 2 planes must be TIMED and coordinated to produce the swing plane.
1 plane- spine tilted, rear to the REAR. The shoulder turn prepindicular to the tilted spine, the arms follow the shoulders, on plane to the ball. The arms work more AROUND the body and across the chest, hence the emphasis on connection.
Differences, 1 plane say turn shoulders from the top, 2 plane says dont. 1 plane core TURNS, 2 tends to tilt. 1 plane has natural width, 2 plane more narrow. which affect the pivot and weight shift.
Transition- 2 plane, 1 st move is a dropping of the hands AND a laterial bump or move towards the target, which does a few things but it also slows the shoulder turn down because if they turned at the start, you would be O.T.T.
1 plane-since you are in essence onplane in the whole backswing going back, simply rotate back on the same plane. The key is to rotate your CORE. If you rotate just the hips, you will tilt, and come out of the shot ( i do this at times, so it hit home with me).
Weight shift, with a 2 plane, he demonstrated how you are pivoting on both hip sockets and it tends to produce laterial moves in both directions back and forward.
1 plane, he really in essence showed the sit down move (my words NOT his), no real laterial moves needed, and said that you could stay on the lead leg and hit good shots.
The main trouble with each that was stressed, 2 plane- the timing needed of the shoulder and arm planes, to produce the swing plane to the ball.
1 plane-the proper CORE rotation, many rotate the hips that cause you to get upper stuck and come out of spine angle.
A swing tip that is given is to move the rear hip or knee towards the ball, with a 1 plane this is improper rotation.
There is a lot more details, but these seem to be the main points that I took from it.