He is best known for extending
Harry Partch's experiments in
just intonation tuning to traditional instruments through his system of notation. Johnston's compositional style was eclectic. He used serial processes, folk song idioms (
string quartets 4, 5, and 10), repetitive processes, traditional forms like
fugue and variations, and intuitive processes. His main goal was "to reestablish just intonation as a viable part of our musical tradition." According to
Mark Swed, "ultimately, what Johnston has done, more than any other composer with roots in the great American musical experiments of the '50s and '60s, is to translate those radical approaches to the nature of music into a music that is immediately apprehensible". Most of Johnston's later works use a large number of pitches, generated through just-intonation procedures. In these works he formed melodies based on an "
otonal" eight-note just-intonation scale made from the 8th through 15th partials of the
harmonic series, or its "utonal" inversion. He then gained new pitches by using common-tone transpositions or inversions. Many of his works also feature an expansive use of just intonation, using high prime
limits. His String Quartet No. 9 uses intervals of the harmonic series as high as the 31st partial. He used "potentially hundreds of pitches per octave," in a way that was "radical without being avant-garde"; in contrast with much twentieth-century music, he used microtones not for the creation of dissonance but in order to "return […] to a kind of musical beauty," which he perceived as diminished in Western music since the adoption of
equal-temperament. "By the beginning of the 1980s he could say of his elaborately microtonal
String Quartet no. 5... 'I have no idea as to how many different pitches it used per octave'". Johnston's early efforts in just composition drew heavily on the accomplishments of post-
Webern serialism. His
7-limit String Quartet no. 4 "Amazing Grace", was commissioned by the Fine Arts Music Foundation of Chicago, and was first recorded by the
Fine Arts Quartet on
Nonesuch Records in 1980 (then reissued on Gasparo as GS205). His String Quartet no. 4, perhaps Johnston's best-known composition, has also been recorded by the
Kronos Quartet. The Kepler Quartet (Sharan Leventhal, Eric Segnitz, Brek Renzelman, and Karl Lavine) also recorded the piece for
New World Records, as part of a complete 10-quartet series documenting Johnston's entire cycle of string quartets. The Third Quartet was premiered as part of this series by the
Concord String Quartet at
Alice Tully Hall at
Lincoln Center for the Performing Arts, on March 15, 1976, the composer's fiftieth birthday.
Staff notation The perfect fifth above D (A, 27/16) is a
syntonic comma (81/80 or 21.5 cents) higher than the
just major sixth above C (A, 5/3), 27/16 ÷ 9/8 = 3/2. Beginning in the 1960s, Johnston proposed an approach to notating music in just intonation (JI), redefining the understanding of conventional symbols (the seven "white" notes, along with the sharps and flats) and adding further
accidentals, each designed to extend the notation into higher
prime limits. Johnston's method is based on a diatonic C major scale tuned in JI, in which the interval between D (9/8 above C) and A (5/3 above C) is one Syntonic comma less than a
Pythagorean perfect fifth 3:2. To write a perfect fifth, Johnston introduces a pair of symbols representing this comma, + and −. Thus, a series of perfect fifths beginning with F would proceed C G D A+ E+ B+. The three conventional white notes A E B are tuned as
Ptolemaic major thirds (5:4,
Ptolemy's intense diatonic scale) above F C G respectively. Johnston introduces new symbols for the septimal ( & ), undecimal ( & ), tridecimal ( & ), and further prime extensions to create an accidental-based exact JI notation for what he has named "extended just intonation". Though "this notation is not tied to any particular
diapason" and the ratios between pitches remain constant, most of Johnston’s works used
A = 440 as the tuning note, making C 264 hertz. In Johnston’s notation a string quartet is tuned C−, G−, D−, A, E. ==Recordings==