Trichord 012 is the most chromatic of all twelve prime forms — three consecutive half steps. Over the available tones of a dominant 7 or 7sus4 it finds six positions; over most other chord types it has none. Chromatic Reasoning shows what a composition built entirely from this concentrated, half-step-saturated structure sounds like over a moving progression.

Trichord 013 is one of the most versatile in the system — it works over all eight chord types. 013 Blues in B places both structures over a blues progression. Art of the Blues contains twelve versions of a blues progression using the 013 trichord with different approaches on each.

Trichord 014 spans a half step and a major third — an interval combination that sits slightly outside familiar triadic shapes while remaining firmly inside the available tones of the chord. Numbers uses both structures of 014 over a standard jazz progression.

Three compositions using trichord 015 are included because 015 is the central example throughout this book. Entanglement and Tangible use Rhythm Changes; SpiderWeb uses the changes to “Back Home in Indiana.” In all three, available chord tones and tensions determine which 015 positions appear.

Trichord 016 contains a tritone — a half step and a tritone in either order. This gives it an edgy, suspended quality that sits particularly well over dominant 7 chords, where it yields eight valid positions. Smoke makes full use of that range.

Trichord 024 is built from two whole steps — the most symmetric of the non-symmetric-feeling trichords, immediately connected to pentatonic and major scale sounds. Grey and Brown isolates that sound and makes it the entire language of the piece.

Trichord 025 spans a whole step and a perfect fourth — a combination that gives it a spacious, open quality. It works over all eight chord types. Beauty Queen shows 025 in a context where that openness is foregrounded.

Trichord 026 combines a whole step and a tritone. Like 016 it yields eight positions over the dominant 7 chord. Derivative works through both structures across a progression that highlights the different colors each structure brings.

Trichord 027 — a whole step and a perfect fifth — is the most naturally resonant of all twelve trichords. It appears in every diatonic scale family and both pentatonic scales. A Day in the Badlands shows what that accessibility sounds like when developed into a complete musical statement.

E-7   Eb°7   D-7   G7   (III-7  bIII°7  II-7  V7)

The melodic étude is the foundation of Sonic Single practice. Constant eighth notes cycle through all valid positions of the trichord over the chord progression, transposed through all twelve keys. Structure S1 appears first, then S2. The goal is even, automatic execution — drilling the trichord positions into muscle memory and ear simultaneously.

This example uses trichord 013 over a minor turnaround (III-7 bIII°7 II-7 V7), Progression 28. The two structures of 013 — a half step plus a minor third (S1) and a minor third plus a half step (S2) — appear in all their valid positions over the minor 7, diminished 7, minor 7, and dominant 7 chords. The audio plays the first key; the full file covers all twelve.

C-7   EbΔ7   AbΔ7   G7   (I-7  bIIIΔ7  bVIΔ7  V7)

The chord étude presents each trichord position as a voiced three-note chord rather than a melodic line — for pianists, guitarists, and anyone working with harmony. The rhythm is a characteristic jazz comping figure. This example uses trichord 027 — a whole step and a perfect fifth — over a minor progression with major 7 substitutions. The open, resonant quality of 027 is especially effective in a chordal context.

CΔ7   Eb7   Ab7   Db7   (IΔ7  bII7  bVI7  bII7)

The étude with rests uses the same trichord positions as the melodic étude but breaks up the constant eighth-note stream with rests. This creates more conversational phrasing — and reveals whether you have truly internalized the material. If the rests feel like interruptions you are fighting against, the underlying étude needs more practice. This example uses trichord 037 (the minor triad) over a descending whole-step progression.

All valid positions of 025 S1 over each chord type — keys of C and F shown

The positions file is a reference document as much as a practice file. Rather than running the trichord over a progression, it isolates each valid position of one structure over one chord type at a time, in all twelve keys. This gives you a direct view of the available tones — exactly which notes of the trichord align with which scale degrees over each chord. Where a chord type shows no positions, the trichord has no available placement over that chord.

026 [0,4,6] — all valid symmetric pairs over each chord type

A symmetric pair is two transpositions of the same trichord that together produce a symmetrical pitch-class set. For trichord 026 S2 — a major third plus a whole step — the symmetric pairs are transpositions where the two 026 trichords share a tritone relationship. The file works through all valid symmetric pairs of 026 S2 over each chord type, in all twelve keys.

037 [0,3,7] — all valid asymmetric pairs over each chord type

An asymmetric pair uses two different transpositions of the trichord that do not form a symmetrical set. For trichord 037 — the minor triad — the asymmetric pairs produce a wider range of harmonic colors. 037 is one of the most harmonically active trichords in the Sonic Twins system because the minor triad appears in so many chord types and scale families.