The Cello Sonata in B-flat major starts with a long line played in octaves between the cello and both hands of the keyboard. It is almost austere in its purity, more like a reservoir of intervals than a true melody. At the end of the string of notes, the piano plays a little rhythmic hook, a snappy, dotted figure. From this playful hint, Mendelssohn builds the ebullient first movement of his sonata. The Andante is a graceful, minor-key dance based on that same dotted figure. For the finale, Mendelssohn returns to the austere shape from the opening of the piece, but he harmonizes it and gives it a new rhythmic character so that it becomes a sweet, nostalgic ditty. We hear this melody again and again over the course of the movement, as if the entire work has served to prepare the listener for this tune, before the music subsides in quiet cascades in the piano. —Nicky Swett