BWV 939 is a prelude in C major by Johann Sebastian Bach, one of the greatest composers of the Baroque era. It is part of his collection of 12 small preludes, which he wrote for educational purposes at different times in his life. The prelude is a short and lively piece that features imitation, which means that the left hand echoes the right hand using the same musical material. The prelude has a simple ABA form, with a contrasting middle section in a minor key that creates some tension and contrast. The prelude ends with a return to the bright and cheerful mood of the beginning.
I hope you enjoy this beautiful piece by Bach.
Before playing any piece it is good practice to play the scales and chords needed in the piece. If you do not know which ones are used and cannot work it out yet and good starting point will be
If the piece is in C major, as this one is, I would start with the following
The scale starting on the tonic or home key and the basic chord. (C major)
The scale of the fourth note (F major) and the chords of the first, fourth and fifth notes of that scale.
The scale of the fifth note ( G major) and the chords of the first, fourth and fifth notes of that scale.
Secondly I would play the related minor scales and chords
The minor scale on the sixth note (A minor) and the chords of the first, fourth and fifth notes of that scale.
The minor scale on the second note (D minor) and the chords of the first, fourth and fifth notes of that scale.
The minor scale on the third note (E minor) and the chords of the first, fourth and fifth notes of that scale.
Finally for added flexibility you can add each scale starting from the fourth and fifth note, whilst maintaining the finger pattern of the original scale.
This brings the mind into what harmonies are going to be used and what you can expect to hear.