The 22-year-old Chinese pianist Lang Lang is already known for his stunning technique. There seems to be nothing his fingers can't do at the keyboard, no composer he can't muscle to the ground. He plays, as Daniel Barenboim once said of him, like he has 11 fingers.
And when he's playing music that needs 11 fingers, Lang is at his mercurial best, as he showed Wednesday night in his Symphony Hall debut. In two Rachmaninoff preludes, he seized the music by the throat and threw it off with not only strength but great musicality. And in Horowitz's arrangement of Liszt's famous Hungarian Rhapsody in C-sharp minor, he made a piece that, by all rights, should be impossible seem merely tricky.
But what of the music that needs only 10 fingers, or fewer? What happens when the contrasts are less violent, the difficulties less tangible, more abstract? There the results were frustrating. When the music became sparer, more reflective, Lang seemed to work to make it more interesting, as if he were trying to keep himself engaged.
Mozart's elegant C-major Sonata (K. 330) was marked by somewhat awkward phrasing and the strange highlighting of individual notes in the texture. In Schumann's ''Kinderszenen" (''Scenes From Childhood") the pianist responded best to its lighthearted, extroverted moments. But he stretched the tempos of its more lyrical pieces so much that the mood of introspection almost dissolved. In both works he seemed intent on guiding the music, rather than letting it unfold.
Chopin's B-minor Sonata illustrated the dilemma perfectly. Moments of bracing intensity, such as the opening and the dazzling runs in the scherzo, were followed by stretches that were pulled around so much that it became impossible to find the musical thread.
It was strange that a performer who can do so much so easily left an impression of such effortful musicianship. The audience, though, cheered wildly. Among the three encores was a tender, nostalgic Chinese song whose title translates as ''The Moonlight Reflects on the Lake." It was the most affecting thing he played all night.