Reprinted from yesterday's late edition.

Less than half a century separates the Piano Somata in B-flat, Op. 47 No. 2 by Muzio Clementi and the great sonata in the same key written by Schubert in the final year of his life. Yet there is a world of difference between the two pieces - most notably in the elements that cannot be set down on paper.

To put it simply, if you play all the notes in the Clementi work as instructed, you have played the music. In the Schubert, the notes are only the beginning of what the composer has to say and what the performer must express if he is to do the music justice. There are infinite subtleties of pedaling, phrasing, dynamics that can take a whole lifetime to work out.

Klaus Hellwig, a young German pianist who played Sunday at the National Gallery, has all the notes well in hand but has barely begun his exploration of what lies beyong the notes.I would like to hear him play these two works again in 20 years; if he grows as he should, the Clementi will probably sound about the same, but the Schubert should have a completely different effect.