Hand-exertion the Basis for the Finger
This basis for the finger should be provided at the right moment by a downward exertion of the hand at the knuckle joint. This exertion of the hand must be precisely timed along with the exertion of the finger itself during the moment of keydepression.
Realize again, that no movement of the hand need be visible however present the exertion of the hand behind the finger.
Hand Basis
Furthermore, the hand also needs its own proper basis during the moment of tone-production, or else the wrist-joint will be driven-up by reaction or recoil.
The result will be that power and accuracy of tone is lost of the weight of the hand is not provided to couteract the recoil upwards.
On separate hands versus hand together playing
In contrast to the common practice of learning (and memorizing) the right hand, then the left hand,
and somehow expecting that to effortlessly merge into a hands together experience, I believe that this way of learning is like learning three pieces and three different situations for the torso:
1) left hand, 2) right hand, and 3) hands together, not one piece. We also teach our non-playing hand not to move when we practice separate hands.
Traditionally pianists diligently learn each hand separately, until the special day when a teacher feels it is “time” to try the hands together. The hands together always feels somehow unrelated to the previous practice.
Playing the separate voices of a Bach fugue hands together after weeks of learning each voice individually can be easily achieved by focusing a different personality on each voice.
I advocate hands together practice as soon as possible. The complexity of the two handed, interdependent experience of playing the instrument can be practiced slowly and then up to tempo.
However, if a fingering needs to be checked, a shape worked out, or a technical issue needs to be solved, we should practice the hands separately.
If someone is injured, the initial work is focused on separate hands in retraining. One should go from practising hands separately to hands together as soon as the motions for each individual hand have been mastered.