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Chord Type Coverage Audit

Updated Aug 27, 2026   |   3.2 KB   |   docs/Chord_Type_Coverage_Audit.md

Chord Type Coverage Audit

Date: 2026-08-17

Executive result

SpaceAge currently exposes 43 named formulas, including triads, suspended and added-tone chords, sixths, sevenths, ninths, elevenths, thirteenths, altered dominants, quartal harmony, a power chord, a Promethean chord, and a free-form cluster. This is broad practical coverage, but no finite dropdown can contain every possible chord. Chords can be extended by adding, altering, or omitting arbitrary degrees; slash basses and polychords multiply the naming possibilities.

The correct product architecture is therefore: a concise musician-friendly catalog for common choices, plus the existing typed-chord/custom-note escape hatch for unusual harmony.

Current catalog

Triad; scale-relative 7th; sus2; sus4; add9; Maj7; min7; 7; minMaj7; dim; dim7; min7b5; aug; augMaj7; 6; min6; 6/9; 9; min9; Maj9; 7b9; 7#9; quartal; 5; Promethean; Maj; min; add11; add#11; 7sus4; 9sus4; 11; min11; Maj11; 13; min13; Maj13; 7b5; 7#5; 7#11; 7b13; min9Maj7; cluster.

Standards comparison

MusicXML 4.0 defines a practical base vocabulary spanning major/minor/augmented/diminished triads; dominant, major, minor, diminished, augmented, half-diminished, and major-minor sevenths; sixths; ninths; elevenths; thirteenths; suspended chords; power chords; and several functional augmented-sixth categories. MusicXML then models additions, alterations, and omissions as degrees layered onto those bases. That confirms that a composable base-plus-degrees model is more complete than attempting an endless flat list.

SpaceAge already covers nearly all common popular-music base families and many useful alterations. Its most meaningful gaps are notation/authoring operations rather than dozens of fixed formulas.

Near-term catalog and aliases

  • add2 and add4 aliases, while preserving their voicing distinction from add9 and add11.
  • Maj7b5, Maj7#5, and minMaj9 musician-facing names/aliases.
  • 7alt as a shorthand family that opens explicit alteration choices rather than guessing one voicing.
  • no3, no5, omit3, and omit5 degree-removal controls.
  • Quintal harmony alongside quartal harmony.
  • Italian, French, and German augmented-sixth labels in the advanced/theory group.

Architectural direction

Represent a chord as:

  1. Base quality.
  2. Added, altered, or omitted degrees.
  3. Optional slash bass.
  4. Voicing and inversion data.
  5. Optional upper structure/polychord.

This mirrors the extensibility of MusicXML and avoids turning the dropdown into an unusable encyclopedia.

Product decision

Do not claim that the dropdown contains every mathematically possible chord. Claim comprehensive practical chord creation: common named chords are one click away, while typed spelling, slash bass, custom clusters, alterations, and future degree controls cover open-ended harmony.

Primary references