The story of Le nozze di Figaro reveals a great deal. We have reached a point in the story of music-making when opera has blossomed. There had been good tunes for the stage for nearly two centuries and an understanding of how drama that told the ancient stories could be adorned by music.

In Italy, and in England when Handel swept to fame in the 1720s, opera became an entertainment for the crowds and an opportunity for the virtuosity of a tunesmith. Handel could write for the popular taste and yet create tableaux of exquisite grace and tenderness with his music. In 18th-century France, Rameau and others were trying to use opera as a vehicle for philosophy, searching for a tragic voice.

Now Mozart produced an opera (his 17th, if you count the fragments) that seemed to do it all. He used familiar forms – farcical misunderstandings, disguise and deceit, a woman singing a man’s part, even the discovery of his long-lost mother by Figaro himself – all the comic apparatus that audiences brought up with the Italian opera buffa would understand and expect. An audience turning up in its finery and getting anything less would feel short-changed.

In his hands the music transformed these conventions, as if characters who had been seen in black and white were now in vivid colour. They shone and sparkled, and exposed their distress. Take the Countess, who wants to reveal her husband to himself but, even more, longs for his love. At her entry at the start of Act II, Mozart gives her the glorious aria Porgi amor, and later, in Act III, while she’s wondering if the plan she has concocted with Susannah will work, she asks: can a lost love be recovered? The aria Dove sono brings spontaneity and refinement together. Nothing seems forced; everything is flawlessly crafted.

Le nozze di Figaro revealed to those first audiences in Vienna what opera could achieve. The door was open to the 19th-century composers who would turn it into a playground for the Romantic imagination. Mozart took a great leap out of the stylised world of Italian opera, in which he had been brought up, carrying his audience with him. The confusion in the garden, and its ultimate resolution, that brings Figaro to an end, was a familiar device. As predictably as in a pantomime, the audiences would get a traditional working out of the story. But Mozart gave them something new. His characters revealed themselves directly. When they sang together they would each tell their own stories, speak from a distinct point of view – they would demonstrate in their trios and quartets how emotions work.

In an age of political uncertainty and coming revolution in which poets and painters were beginning to delve inside themselves for inspiration, letting their emotions speak, opera was evolving too. When the story is almost over, and we know the Count is going to improve his ways, he asks for forgiveness from his wife. As the curtain falls, we hear more than the satisfying end of a story neatly finished. We hear opera transformed.

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