Of Mozart's many fundamental contributions to opera, perhaps none is more significant than the development of the idea that the orchestra could provide music that influenced the action just as easily as the unaccompanied recitatives do. No longer were the instrumentally accompanied sections purely commenting on static situations - the composer as dramatist became equally present whether the orchestra were playing or not. The timing of Mozart's conducted music is inevitably more pre-ordained than the recits, but it contains plenty of opportunity for the freedom and variation that affects the dramatic pacing of a performance as a whole.

One of the most obvious examples of this is Mozart's use of the pause. Superficially a musical request, the motivation and result is nevertheless always intended to be dramatic. A pause is an undefined moment of indecision that takes time but never stops: lingering in suspension and pregnant with possibilities. Whether it's written on a note or on a silence makes no difference - the spontaneous hesitation is both lifelike and thrilling. Mozart's pauses make abundantly clear his attitude to dramatic pacing and it is fascinating, albeit perhaps rather nerdy, to compare their use in two of his operas.

Don Giovanni is a man characterised by actions, not thoughts. He is always in a rush, and never once considers what the repercussions might be. 'Manic self-propulsion in perpetual motion' is Hans Joachim Kreutzer's brilliant description. Indeed it's probably his refusal to stop and think that keeps him going. Kierkegaard likened it to skimming a stone over the surface of the water: 'it skips lightly for a time, but as soon as it ceases to skip, it instantly sinks down into the depths.' Over the course of the constantly driven and compulsive opera Mozart specifically writes for the singers and orchestra to pause on 35 occasions - a meaningless figure until one compares it with the 150 he writes in an opera of similar length - Cosi fan Tutte.

Cosi is a piece about suspicion and insecurity. A game that started as a joke brings the characters face to face with serious questions whose answers profoundly affect the rest of their lives. The choices they make have significant consequences and need time and thought to get right. Whilst Don Giovanni has all the inevitability of a roller-coaster that does not let up until the final curtain, Cosi is an uneasy merry-go-round of doubt and confusion that actually never reaches a conclusion at all. The extraordinary difference in the number of pauses is totally appropriate for such contrasting operas.

Both Don Giovanni and Cosi fan Tutte offer complete experiences and listening to one never makes me wish I was hearing the other. The breathless absence of pauses in one is just as exciting as their uncertain profusion in the other. Like most things connected with Mozart, the pause is a simple device employed to perfection. Whether he is asking us to get carried away or to sit and reflect, we are completely under his spell.