In the middle of this slow movement lies a sublime quiet passage for piano and two clarinets that stands out as a unique moment in the concerto. Time seems to stand still as slow rising arpeggios in the piano accompany long sustained notes in two clarinets. This is a musical moment as removed from the momentum of a concerto as one can imagine. But from where does this music come? It is not at all clear, since it sounds entirely different from the rest of this slow movement.
The movement begins with an expressive cello solo, so overwhelming a melody that we joke Brahms has decided to convert his piano concerto into a cello concerto. But if you are familiar know some of Brahms’ tricks, you guess that simple descending scale in the low strings that accompanies the cello melody is not just there for show. In reality, this descending scale is what controls the development of the piece, not the bewitching melody above it. Brahms loves to take a subtle background element and reveal it later as foreground, an irony that makes listening to his music a continuing process of discovery.
We don’t have long to wait to hear his intentions with this descending scale. After the cello finishes its first phrase, the violins imperceptibly enter and sustain a high tone over the cello’s second phrase. This high tone descends ever so slowly by step, harmonizing with the cello until it resolves on the very note with which the cello began its melody. Now the violins pick up speed and play that same melody an octave higher. For us listeners, it seems that the violins came out of nowhere and just suddenly appear at the right place and time to echo the cello’s tune. But their entrance with that long sustained high tone began an augmentation—a stretching out—of that very descending scale the low strings first wept down beneath the solo cello.
Just before the piano enters—to remind us that indeed we are still in the middle of a piano concerto (!)— a bridge section brings the scale to the surface. The cello itself, along with the oboe, plays the augmented descending scale accompanying the violins as they finish the tune. After the piano enters with two rising arpeggios, it too plays variations of this descending scale, in a style strongly reminiscent of the slow movement of Beethoven’s Emperor Concerto (#5).
The point is not merely that Brahms focuses increasingly on the descending scale, but that in augmenting the scale so early in piece with the violins, he is anticipating the magical time stretching at the heart of this movement with the piano and clarinets. And indeed, the long descending notes of that clarinet duet are the same notes of the descending accompaniment from the opening, just slowed down even more, to the point we don’t readily recognize them as even falling. The sense that this music is something quite new, yet derives in some way from what came previously, is a special kind of “time travel” or temporal development. It’s a device that later composers like Mahler and Schoenberg used continually to enter new realms of texture. But here it creates a special emotional interior for the entire piano concerto.