It's always good to be reminded that the written note is really only a starting point, a cryptic suggestion from the composer. The phenomenon is downright startling when listening to Mitsuko Uchida. The pianist was back Friday night at the Perelman Theater for one of her periodic visits with the Philadelphia Chamber Music Society, and while there were only a few moments in her playing you could call radical, there were dozens of spots when you realized that just hearing the notes played straight – with no changes in tone or special distortions in pacing – would have robbed you of the real emotional meaning of the music.

Her recital, sold out, was all Schubert – three sonatas. Part of Uchida's appeal is surely in her technical risk-taking. In the Piano Sonata in C Minor, D. 958, she deployed dynamic changes in the first movement so suddenly and completely that she sometimes seemed like more than one pianist, and she created the beautiful illusion of a pizzicato effect in the second. She solved a common problem in the manic fourth movement by connecting certain far-flung notes that, in other hands, can make the music sound silly or trite.

But Uchida's real allure, I think, comes from her unpredictability. She kept a steady inner beat in the first movement of the light-filled Piano Sonata in A Major, K. 664, except when she didn't. Her tone grew urgent or wan, depending on the mood. She brought certain figures or voices to the foreground while suppressing others, and choices weren't always the obvious ones. Impetuousness in the fourth movement was her stock-in-trade.

The third sonata on the program, the Piano Sonata in G Major, D. 894 is a world unto itself, not only because of the length and the extent to which Schubert develops his ideas, but also because of the incredible variety of character Schubert creates within the prescribed sonata form. Uchida pushed its emotional complexities way beyond the mere opposing poles of tension and release, or tragedy and elation. She created a feeling of great instability once the development of material began in the first movement. The second alternated between serenity and music of peril, and when the music grew dangerous, the pianist really caught fire. Her reasons for drawing out the four penultimate notes of the second movement? Nothing in the manuscript requests it. But it created a kind of musical question mark whose answer came with the first few notes of the third movement.

Every pianist has his or her own way with the "Trio" section of D. 894's third movement, a sweet, folk-inspired dance. Uchida created a hush, of course, as many do. But the way she sculpted the recurring ornament was mind-boggling in its quickness and subtlety – more Italianate, as in Scarlatti, than anything Austrian. On the page, that ornament is a little squiggle called a mordent, instructing the player that the note should quickly alternate with one next to it. Most pianists know how to manage it elegantly. Uchida made it elegant, but she also deepened the complexity in a way that heightened the feeling of being without gravity, of no longer being tethered to Earth. This is what we come to artists for.