Shaping is the Choreography of the Hands

Physical shaping is produced as an 1) under-shape or 2) an over-shape. It comes about through a combination of all the movements necessary to play a passage, such as

1. the walking-arm,
2. the in-and-out of the upperarm, and
3. the up and down of the wrist.

These movements become welded in a sort of fluid motion with a different shape for each passage. The correct combination of long and short fingers on black keys and white keys leads to the proper combination of the fingers and arm so that they play as a unit.
Shaping is the shortest route to align all movements so that facility and fluency come easily to a passage. If shaping does not work, it may be that one finger in the in-and-out movement is in the wrong location in the depth dimension. Fortunately, the process is a natural one and the hand will begin to sense the correct shape, and the player will not have to think about each note in advance.

Prodigies instinctively know these movements. When a sudden change of hand direction develops in a passage, there is danger of an angular shape developing. The best thing to do would be to continue in a curvilinear motion by adding an under-shape when the direction of play is reversed. Shaping gives the means to enhance the color and inflection of each note in a phrase, for every note in that phrase has its own influence. When playing larger distances the shaping is bigger, but the shaping must be at that degree so that any less shaping would prevent it from working.