The Four Triads
A triad is a 3-note chord built by stacking two 3rd intervals above a root. The quality of those 3rds determines the triad type. All of Western harmony starts here.
| Triad | Formula | Semitones | Sound |
|---|---|---|---|
| Major | 1 — 3 — 5 | 0 — 4 — 7 | Bright, stable, resolved |
| Minor | 1 — ♭3 — 5 | 0 — 3 — 7 | Darker, introspective, complete |
| Diminished | 1 — ♭3 — ♭5 | 0 — 3 — 6 | Tense, unstable, dissonant |
| Augmented | 1 — 3 — ♯5 | 0 — 4 — 8 | Mysterious, floating, unresolved |
The difference between major and minor is one semitone — the ♭3. Lower the 3rd of any major chord by one fret and you get the minor version. This is why the 3rd is called the harmonic identity note: it determines whether a chord is major or minor, happy or sad.
Diminished is built from two stacked minor 3rds (3+3 = 6 semitones total). The ♭5 creates a tritone above the root, which is why diminished chords sound so tense. Augmented stacks two major 3rds (4+4 = 8 semitones). It's fully symmetric — any note in an augmented triad can function as the root.
Sus Chords
Suspended chords replace the 3rd with either the 2nd (sus2) or the 4th (sus4). Without a 3rd, the chord has no major/minor quality — it sounds ambiguous, open, and unresolved.
- Sus2: 1 — 2 — 5 (semitones: 0-2-7). Open, contemporary, floating.
- Sus4: 1 — 4 — 5 (semitones: 0-5-7). More tension than sus2; the 4th wants to resolve down to the major 3rd.
The resolution of sus4 → major is one of the most satisfying moves in Western music: Csus4 (C-F-G) → C major (C-E-G). The F drops a half step to E. You hear this in "Pinball Wizard" (The Who) and countless others.
7th Chords — Adding Color to the Triad
A 7th chord adds one more 3rd above the triad, giving you 4 notes. The type of 7th (major 7th = 11 semitones, or minor 7th = 10 semitones) combined with the triad type produces different 7th chord qualities.
| Chord | Formula | Semitones | Where it appears |
|---|---|---|---|
| Major 7 (Maj7) | 1-3-5-7 | 0-4-7-11 | IMaj7, IVMaj7 in major keys |
| Dominant 7 (7) | 1-3-5-♭7 | 0-4-7-10 | V7 in major keys; all blues chords |
| Minor 7 (m7) | 1-♭3-5-♭7 | 0-3-7-10 | ii7, iii7, vi7 in major keys |
| Half Dim (m7♭5) | 1-♭3-♭5-♭7 | 0-3-6-10 | vii∅7 in major; ii∅7 in minor |
| Fully Dim (°7) | 1-♭3-♭5-♭♭7 | 0-3-6-9 | Chromatic passing chord; harmonic minor |
| Minor-Maj 7 | 1-♭3-5-7 | 0-3-7-11 | iMaj7 in harmonic minor; cinematic tension |
The Tritone and Why Dominant 7th Chords Resolve
The dominant 7th chord (major triad + minor 7th) has a built-in tension mechanism: the tritone between its 3rd and its ♭7th. In G7, that's B (the major 3rd) and F (the minor 7th) — a tritone apart, 6 semitones, maximum dissonance.
When G7 resolves to C major, that tritone collapses inward: B moves up a half step to C, and F moves down a half step to E. The most dissonant interval in the chord resolves by half steps to the most consonant notes of the destination chord. This is why V7→I sounds so satisfying — the tritone resolution is a physical release of harmonic tension.
Every ii-V-I progression, every blues turnaround, every classical cadence works because of this mechanism. Dominant 7th chords create tension; major chords release it.
Guide Tones: The 3rd and 7th
In any 7th chord, the 3rd and 7th carry the harmonic identity. The root and 5th are structural but not distinctive — they tell you little about the chord quality. The 3rd tells you major or minor; the 7th tells you major 7th, dominant 7th, or minor 7th. Those two notes define the chord.
This is why advanced jazz musicians practice "guide tone lines" — playing only the 3rd and 7th of each chord through a chord progression. Two-note voice leading through an entire song. It sounds thin but reveals harmonic structure with crystalline clarity.
A daily 20-minute practice of playing through a standard like "Autumn Leaves" using only the 3rds and 7ths of each chord is one of the most efficient exercises for developing harmonic hearing. The goal is to hear the chord quality from just those two notes, and to find the smoothest voice leading between guide tones on adjacent chords.
Exercise 1
Major → Minor → Diminished on 3 Strings
Find a major triad on the top 3 strings (strings 1, 2, 3) at any fret. For C major: E-string fret 8 (C), B-string fret 5 (E), G-string fret 5 (C) — or use a standard root-position voicing you know. Now flatten the 3rd by one fret (from E to E♭) — that's C minor. Now flatten the 5th by one fret too (from G to G♭) — that's C diminished. Three chord qualities, three shapes, all from moving one note at a time. Do this starting from 5 different root positions.
Load Major Triad on fretboard →Exercise 2
Guide Tone Resolution: G7 → CMaj7
Find the guide tones of G7: B (the major 3rd, found on string 2 fret 0 or string 3 fret 4) and F (the minor 7th, found on string 1 fret 1 or string 2 fret 6). Play just those two notes together. Now resolve them to the guide tones of CMaj7: C and E. B moves up one semitone to C. F moves down one semitone to E. Play this resolution slowly several times. This voice leading — the tritone collapsing inward — is the engine of tonal harmony. Then apply it to Dm7 → G7 → CMaj7 (the ii-V-I).
Load Dominant 7 on fretboard →Extended Chords: 9ths, 11ths, 13ths
Extended chords continue stacking 3rds above the 7th chord. The 9th is an octave above the 2nd; the 11th is an octave above the 4th; the 13th is an octave above the 6th. Theoretically, a 13th chord contains all 7 notes of the scale stacked in thirds.
In practice, extended chords are voiced selectively — you choose which notes to include and which to omit. The 5th is almost always dropped. The 3rd is sometimes dropped in 11th chords (because it clashes with the 11th). What remains are the notes that create the specific color you're after.
The pattern on the NeckSight fretboard makes this clear: a dom9 chord (0-4-7-10-14) highlights the 2nd scale degree in addition to the basic dominant 7th structure. Remove the 5th in practice, and you have a compact, rich voicing that defines jazz and R&B harmony.
Challenge
Spell Out Three Chords
Without using the fretboard tool, spell out the notes (not intervals — actual note names) of these three chords: (1) B♭ minor 7, (2) F♯ half-diminished (m7♭5), (3) E♭ dominant 9. For each: identify the root, then count up the semitone intervals from the formula. Check: B♭m7 = B♭-D♭-F-A♭. F♯∅7 = F♯-A-C-E. E♭9 = E♭-G-B♭-D♭-F. If any surprised you, work backward from the chord name — what formula must it follow?
Building a chord from its formula is one thing. Understanding how chords connect — why some progressions feel inevitable, what drives V→I, and how ii-V-I became the backbone of jazz — is what comes next.