Fryderyk Chopin, daguerreotype from 1849. Via Wikimedia Commons (public domain).
Among the Italian words music has given the world, rubato is the most misunderstood. In common usage it means playing with freedom, slowing down where it feels good; in the original idea it means something far more precise and far harder: stealing time from one note to give it to another, with the obligation to balance the books. Theft with restitution.
The word appears in print in 1723, in Tosi’s treatise on singing, and it matters that it was born from singing: a singer breathes, and breath is not a metronome. But the supreme codifier was Chopin, and his rule, handed down by his pupils, is one of the loveliest images in music teaching: the left hand is the Kapellmeister and will not compromise, the right does what it likes. Below, the accompaniment keeps time like a clock; above, the melody anticipates, delays, lingers on a beloved note and then runs to rejoin the group. The two hands part and meet again, and the thrill lies exactly there, in the elastic that stretches and snaps back. Liszt used a poet’s image: the wind that stirs the leaves while the tree does not move.
True rubato is therefore a matter of structure, not of feeling: it works only if somewhere the time stays still. When instead everything slows together, melody and accompaniment, it is not rubato, it is a rallentando, legitimate but different, and the first recordings of the twentieth century document how much styles have changed: pianists of the nineteenth-century school arpeggiated chords and staggered their hands in a way that today sounds almost scandalous, and that was then the height of elegance. The history of taste passes through these millimetres, as with vibrato: every age is convinced that its own balance between order and freedom is the natural one, and every age is wrong.
The listening exercise: take a Chopin nocturne in a great interpretation and listen only to the left hand for a minute. You will hear an almost regular beat, a gentle clock. Then climb back up to the right: everything that moves you lives in the gap between the two. Rubato is the sonic proof that freedom needs something that does not move in order to be perceived: without the Kapellmeister in the left hand, the right is not free, it is merely late.