An accomplished pianist himself, Foss had not written for the piano over a span of 28 years before composing Solo in 1981. The composer says, "An initial 12-tone motive reigns. Yet this is not 12-tone music. The motive is like a theme that undergoes constant development. Nor is this minimal music, in spite of an insistent, repetitive element, because each repetition is also a change implying development, growth and forward movement." In 1982, Foss added a small ensemble of vibraphone (or marimba), harp (or cello), and organ (or accordion), which joins the piano well into the piece, creating a new version titled Solo Observed. "Foss was at the keyboard for his Solo Observed, with a fiendishly difficult piano part that chugged along for more than five minutes before the entry of cello, organ and vibraphone. At that point the initially atonal piece morphed into a jazzy romp before quietly fading out with an additional piano measure. Foss brought all of this off with great sophistication and wit." (Alan Becker, Sun Sentinel, April 16, 2002)