20th-century forms: arch, block, moment, open and process form

Why new forms are needed

When functional tonality weakens in the 20th century (atonality, modality, polytonality, serialism), sonata form loses its engine: the contrast between the tonic and other keys. Composers look for other principles to organize time: symmetry, juxtaposition of blocks, autonomous moments, the performer's choice, gradual processes. Many of these principles are today the basis of electronic, ambient and screen music.

Arch form (palindromic)

• Symmetrical scheme A–B–C–B′–A′: the sections (or movements) correspond in mirror image around a center.
• Bartók: String Quartets No. 4 (1928) and No. 5 (1934), both in five movements with the first linked to the fifth, the second to the fourth and the third as the center. The first movement of Music for Strings, Percussion and Celesta (1936) is a fugue with an arc of dynamics and density: the entries start on A and move away by fifths in both directions up to the climax, then return toward A.
• Some scholars (Ernő Lendvai) have read in Bartók proportions based on the golden section; these readings are debated and not always confirmed by measurements.

Block form (juxtaposition)

• Contrasting sections placed side by side without transitions, which return and alternate like panels.
• Stravinsky: The Rite of Spring (1913) and above all Symphonies of Wind Instruments (1920), built from blocks that interrupt each other; Messiaen takes up the principle.
• Today: film editing and "collage" tracks (see the entry on K-pop) use the same logic.

Moment form (Momentform)

• Theorized by Karlheinz Stockhausen (Kontakte, 1958–60; Momente, 1962–69): each "moment" is an autonomous section with its own character, which does not "lead" to the next; listening happens in the present, without a path of tension–resolution toward a climax.

Open or mobile form

• The order of the sections is decided by the performer or by chance: Stockhausen, Klavierstück XI (1956), 19 fragments on a large sheet to be played in random order; Boulez, Third Piano Sonata; the indeterminate scores of John Cage.
• It anticipates the adaptive music of video games, in which sections are combined according to the action.

Process form (minimalism)

• The form is the result of a gradual, audible process applied to minimal material (Steve Reich, essay "Music as a Gradual Process," 1968).
• Phasing: two performers play the same pattern, one speeds up imperceptibly and the phase shift generates new patterns (Reich, Piano Phase, 1967).
• Additive processes: a pattern grows note by note (Philip Glass, Music in Fifths, Einstein on the Beach, 1976).
• Form in pulse sections: Reich, Music for 18 Musicians (1976), built on a cycle of 11 chords, each of which becomes the basis of a section.

Twelve-tone music and traditional forms

Many serial composers instead use classical forms to give clarity to a new language: Schoenberg, Suite for Piano, Op. 25 (prelude, gavotte, musette, intermezzo, minuet, gigue); Webern, Variations, Op. 27; Berg, tight forms (passacaglia, rondo, variations) in the scenes of Wozzeck (1925).

How to analyze a 20th-century form

1. Identify the sections by non-tonal criteria: density, register, timbre, tempo, dynamics, material (pitch sets, rows).
2. Draw a graph over time (timestamps on the x-axis, density or register on the y-axis): it often reveals arches, blocks or processes.
3. Look for correspondences (symmetries, returns).
4. Ask yourself whether there is a goal (climax, resolution) or whether the form is "static."

For a producer

• Process form is the basis of techno and ambient music: a loop that gradually transforms (filter, adding notes, phasing between two slightly different delays).
• Block form is the principle of the beat switch and of editing for video.
• Arch form is useful for instrumental tracks and mirrored intros/outros.

Exercise: create a 3-minute track with two identical 8-note loops on two channels, one at 120 BPM and the other at 120.5 BPM (or with a shifting delay), and let the phase shift build the form.

Related entries

Minimalist composition: additive processes and phasing, Fugue: formal plan (Bartók), Video game music: loops and adaptive music, Set theory, Schoenberg: from extended tonality to atonality and twelve-tone music, Dance break and beat switch in K-pop.