Soft and loud in music might be compared to transparent and opaque--I think of watercolor vs. oil paint. Mozart specified dynamics very clearly. It's not that a musical idea was to be played softly; it was soft. Soft was part of its essence.

The subject came up today in the Prelude to Schumann's Kleine Fuge in The Album for the Young. The sonorities seem to invite upbeat playing, yet the designation piano indicates that something more subtle is going on. The forte coming later is not prepared by a crescendo, as one might expect, but by a diminuendo! Lots to think about.