Rhythms are quickly wearisome, unless refreshed by a countervailing foreground which groups the tones against the metre. The ever‐so‐slight rubato of a solo instrument playing in front of the beat is familiar to jazzlovers. To play jazz properly it is not enough to move with the beat: you must also enter the ‘groove’ of it, which means riding alongside it with those playful gestures that ruffle the rhythmic surface and fill it with light. The distinction between beat and groove is a special case of the general distinction between foreground and background rhythm.