In Mozart, what goes up, must come down. Just think of the most famous example in his music, the opening gambit of "Eine Kleine Nachtmusik." Dum, da dum, da da da da da dum. Pause. Then, right back down again. A perfect balance achieved, a universal concept confirmed, the Classical style in miniature. Equilibrium permeates this composer's art, not just up with down but soft with loud, low with high, ebb with flow, virtuosic with expressive, strings with woodwinds. His would seem to be the music of Newton's Third Law: "For every action, there is an equal and opposite reaction."
But it's not that simple. Though the cold laws of physics play their part, Mozart is also the most human of composers. The defining characteristic of his melodies, whether they are played by an instrument or expressed through the voice, is their singing quality: The connected lyricism of their line, the room left for inhaling, the phrase length equal to a single human breath. The sheer tunefulness of his melody both mimics and exults folk song. "The Magic Flute" could be danced by costumed peasants on the village green. Play me one of Mozart's piano concertos and I'll show you an opera by other means.
The tunes are simple and basic, yet exquisite like jewels. Bach's melodies are mechanical by comparison. Haydn had no such gift for vocal melody. Beethoven usually wrote motifs and themes, instrumental in character, not melodies. (Even the great "Ode to Joy" melody has a certain "composed" quality about it.) Brahms sculpted his themes out of clay (and never did write an opera). Wagner is for superhumans. Perhaps only Schubert had Mozart's talent for singing melody, though he took it in another direction. In Schubert, every action is an action, to be felt to the full, not mediated, moderated or balanced in any way.
Next week, on January 27 to be precise, Joannes Chrysostomus Wolfgangus Theophilus (the Latin form of Amadeus) Mozart turns 250. The world of classical music will be celebrating the occasion, all year long. In one of the more impressive undertakings, in his hometown, at the Salzburg Festival this summer, all 22 of his operas and opera fragments will be performed.