Johann Sebastian Bach wrote a set of fifteen two part inventions in the 1720’s to help his son Wilhelm Friedemann Bach learn to play the harpsichord. They are composed as if they were for two separate instruments, and so there are never more than two notes sounding at once. One note in the right hand and one in the left hand, each playing an independent melody.
Neither hand is more important than the other in these pieces, both melodies are equally important. To play these pieces well you have to become two musicians playing at once, and it is one of the hardest things to do in music. Hence then name; Two-Part Inventions.
These pieces are deceptively simple. They actually are the best training in gaining independence of the hands when playing the piano. Bach actually says in the preface to his book that you will learn to play both parts clearly.
This is more important than it might seem. Often when we play the piano we think of chords and all the notes going down at once. But actually all music, including piano music, is composed of horizontal musical melodies, and the better we get at making them musical the better we get at being expressive musicians.
Bach’s two-part inventions are lovely pieces, they are challenging and immensely satisfying to play, and they provide training in one of the most important aspects of good piano playing.