Stealing time
Stage 3 taught you to read the tempo instructions — rit., accel., rubato. This lesson is about doing it yourself, in a phrase that has no marking at all, because the music wants it. The word is rubato — Italian for "robbed" — and the rule that keeps it from turning into a mess is: steal time, then give it back.
Steal, and repay
A phrase has a shape: it presses toward a high point and settles toward its close. Time can follow that shape — hurry a little into the rise, broaden on the peak, then ease back so the phrase still ends where the pulse says it should. What you took at the top, you repay on the way down. The bar lands on time; the inside of it breathed.
How to play it
Nothing here is big. A hurried note is maybe 10% faster; a broadened one maybe 20% slower. If a listener can 'hear the rubato' as an event, it's too much.
Leopold Mozart's picture
He described rubato as the melody pressing ahead and falling back while the accompaniment keeps strict time — the tension between the two is the expression. Chopin said the same a century later: the left hand is the conductor and keeps time; the right hand is free over it. On a solo line you play both roles — one part of you keeps the pulse, another part bends over it.
Where it belongs — and where it doesn't
Rubato is generous in Chopin, Kreisler, late-Romantic playing — a real, audible ebb and flow. In Mozart it's tiny and structural: a hair of space before an important arrival, a breath at a phrase end, never a wilful slowing. Playing Mozart with Romantic rubato is the same style error as playing him with Romantic vibrato (Movement F).
Try it
Try
Play the phrase above once locked to a metronome — rigid. Then turn the metronome off and "breathe" it: forward into the peak, broaden on the D, repay it coming down. Record both. The rigid one is correct; the breathed one is music — as long as the last note still lands where the rigid one did.
The usual mistake
Stealing time and never giving it back — the phrase just gets slower and slower and the pulse dissolves. Rubato is a loan, not a gift. The opposite mistake is rubato so constant and wilful that there's no steady pulse left for it to pull against.