It's a given that every composer profits from the study of Bach. This was true even during the late-18th century, when audiences rejected his dense "learned" style in favor of the lighter galant. Mozart's own exposure to the Baroque master was indebted to Baron Gottfried van Swieten during his early days in Vienna. As he recounted in a 1782 letter to his sister: "Baron van Suiten [sic], whom I visit every Sunday, gave me all the works of Handel and Sebastian Bach to take home with me after I had played them through to him. When Constanze heard the fugues she fell quite in love with them. She will listen to nothing but fugues now…. Having often heard me play fugues off the top of my head, she asked if I had ever written any down, and when I said I had not, she scolded me very thoroughly for not having written anything in this most artistic and beautiful of musical forms…." The 26-year-old's lighthearted tone masks a more profound emotion; as Alfred Einstein pointed out more than 50 years ago, Mozart's study of Bach's fugues represented "a revolution and a crisis in his creative activity," internalized through string arrangements of Bach fugues and reflected in major compositions - directly in the Requiem and the "Jupiter" Symphony, more diffusely in the increasingly polyphonic conception of many works from his last decade.

The C-minor Fugue was first composed in December of 1783 for two pianos (K. 426) then re-arranged for strings, with an introductory Adagio, in June 1788 - the prolific summer during which he also penned his last three symphonies. The Adagio alternates a dotted-rhythm reminiscent of a French overture with a more lyrical passage. A French overture normally begins a more extended multi-movement work; in this case, its use serves to establish a period flavor and a sense of occasion. The theme of the Fugue is strongly rhythmic, with little of Mozart's melodic charm - and yet it has the uniquely Mozartean quality of suggesting a character through gesture and nuance. The "crisis in creative activity" was not for naught.

- Susan Key is a musicologist and frequent contributor to Los Angeles Philharmonic programs, specializing in American music.