There aren't very many really revolutionary pieces of music in this century or any other: pieces that seem like cultural mutations that spring spontaneously into being without visible or audible precedent. Le sacre du printemps is an authentic example. So, I believe, is Terry Riley's In C. In C is tangentially influenced by rhythmically and melodically insistent passages in Satie and Cage, and Asian music.

In C's energy levels are on a par with little in classical music, though; they more nearly match those of rock and hard-driving jazz. The comparison to Le sacre is apt in another sense because it contains passages of energy and insistence comparable to that of In C. Riley's shifting, trebly colors and modal melodies are very reminiscent of Russian folk melodies as treated by Mussorgsky and Stravinsky.

In C's structure is simplicity itself: it is a loose-jointed canon at the unison for a fairly large ensemble of treble instruments propelled by a repeated piano C octave in eight notes that starts, finishes, and meters out the entire fabric. (This ostinato C demands a stalwart piano player indeed, for performances of In C usually run at least 40 minutes, perhaps as many as 90. The ostinatist must produce a series of from about 6,000 to perhaps 15,000 equally paced identical pulses at C octave, which has turned some pianists into dodos, at least temporarily.)

The other more fortunate players perform a series of 53 individual rhythmic/melodic riffs varying from just one eighth note to an expansive 60 eighth notes in length and in pitch from G to B2 (a little over 2 octaves). The order of riffs is fixed, but each player is free to repeat them as many times as s/he chooses and enter and leave the ensemble at will as long as he or she does not stray too far from the "path." The effect is of a sparkling, glinting crystal which, as it slowly rotates, changes almost imperceptibly in color from a clear C major to a bright, yet more slowly pulsating, E minor then back to C rather triumphantly, and finally takes on the cast of a much more somber and enigmatic G minor. In C unquestionably belongs, to my mind at least, to the elite group of great elaborations of C tonality, including Bach's Overture No. 1, Mozart's "Jupiter" Symphony, Schubert's Cello Quintet, and the Sibelius Third and Seventh Symphonies. Even though Terry Riley has spent much of his creative life in New York, he is a Western American by birth, and musical inclination - as such in the company of Harry Partch, Lou Harrison, John Cage, Pauline Oliveros, La Monte Young, and Henry Cowell, among others. Certain qualities of this americanus occidentalis set the breed apart from others - a kind of mystic pragmatism, a sometime superficial but fructifying contact with Asian culture and philosophy, and an extroverted, cheerful mistrust of the intellectual reserve and clannishness found among a lot of present day composers, particularly Europeans and East Coast Americans.

- Douglas Leedy, 1992. From the liner notes to "In C: 25th Anniversary Concert," New Albion NA 017 CD.