Bach's English Suite in A Minor: Oh No, Three Voices

      My student brought the prelude to Bach's A 

J.S. Bach

Minor English Suite, which he played quite fluently and with excellent understanding of the style. He knows not to accept "just okay" technically, because he knows complete ease is possible. So, he asked me about measure nineteen, where the bass note is held while the tenor rambles about in the same hand. Although he could play the notes so that they sounded just fine, he felt constricted. Clever lad that he is, he asked about the rotation.

Bach A Minor English Suite, M 19 Prelude, Rotation

     Remember, forearm rotation is only an underlying tool. The concept sometimes confuses and confounds the uninitiated, especially absent an in-person demonstration. In this case, feeling the difference between single and double rotation can help to unlock the hand where it feels constricted. Admittedly, this example is a somewhat small point, but working in the rotation here can have a profound result elsewhere.
     Notice the angled arrows in the example. The angle indicates the direction from which the finger strikes the key. Since the fifth finger remains in place, the rotation can't be very exaggerated. This is fine, because we always want tiny movements for speed anyway. Where there are consecutive arrows in the same direction, the movement is called a double rotation, rotating both to and from a note. When the music changes direction with each note, the movement is called single rotation. This is what most pianists think of when forearm rotation is mentioned; it is what occurs in an Alberti bass figure or a trill. (For more on forearm rotation and other issues, see Piano Technique Demystified: Insights into Problem Solving.)
     What happens here, then, in measure nineteen, is a release of tension in the left hand, slight though it may be, by allowing the rotation its freedom. The result is an avoidance of finger isolation.

There's more to it than spinning.

      It turned out, though, that there was also a coordination issue in my student's approach. We pianists learn from day one to spin a musical line beautifully to the right. This is good. But what if we have two or more lines that crave spinning beautifully to the right. What then?
     Ah. I'm glad you asked. We have to ween ourselves from the horizontal and consider the vertical. That is, what happens at points (as in counterpoints) where the voices come together. Here, if there is a coordination issue, we have to feel the combined downs, the "verticalness" as indicate by the doubled-headed arrows in the example.

Bach A Minor English Suite, M 19 Prelude, Verticalness

          Practice stopping on each eighth and notice which two fingers are partnered. Feel the down into the keys in each hand. My teacher used to say, 
"Dear, the piano is down. We only come up in order to go down again." Say the finger numbers numbers aloud. Notice how the pairs change. I know it seems silly, but do it. It works. (For more on coordination in contrapuntal music, see Demystifying Bach at the Piano: Problem Solving in the Inventions and Sinfonias.)