This brings to light the necessity for carefully distinguishing between

1. a movement made free from external resistance and
2. the similar movement made against external resistance.

The distinction grows in importance in the psychological phases of piano technique. In all percussive touches the attainment of the desired tonal effect can be shown to depend primarily upon the person knowing ahead of time, the type of tone desired before the movement is initiated. To practice the movement without the tonal result is, so far as its direct effect upon the application of the movement is concerned, psychologically unsound.

The mechanical, silent , keyboard devices lose in value because of this fact.
This does not mean, however, that practice of movement without resistance is of no pedagogical value. On the contrary, such practice is the best and surest way of teaching the misnamed, but technically helpful isolation of movement.
The records given in this module show that with resistance there is a reaction at other joints. The inhibition of this reaction demands a spread of tension over these joints and hence directly opposes the aim of the movement, which is isolation. By working from the zero point of intensity to the louder degrees, we proceed from minimal to maximal muscular spread. On the other hand, to demand of a pupil a tone production of even moderate loudness with the finger, while the other joints of the hand and arm are fully relaxed, is to demand the impossible.

Action and reaction are present also, and operate the same way when the key-attack is so short that muscular adjustments cannot be made during key-depression. When, for example, a chord is played loudly and quickly, the hand is firmly fixed as the arm descends and before the key is struck. The reaction, I might say, is present before the act ion causing it . This contradiction is only apparent . What actually happens is that the player images the key-resistance, and hence prepares the spread of muscular contraction, the necessary fixation of the joints, before the key is reached. Through experience and talent this image can function very accurately, and upon its accuracy depends the question of whether or not the player will get the desired tonal result. Insufficient fixation or an excess thereof, is to be classed as in-coordinated movement, because, from the standpoint of interaction, a coordinated movement is one in which act ion and reaction are equal and opposite. It is the physiological application of the physical principle of the parallelepiped of forces, which defines a point at rest as acted upon by forces whose directions are opposite and whose magnitudes are equal.