In This Guide
1 How Chords Are Built from Intervals
Every chord in music is constructed by stacking intervals above a root note. The most basic chords, triads, are built by stacking two intervals of a third (either major or minor) on top of each other. The specific combination of major and minor thirds determines the chord quality, whether it sounds major, minor, diminished, or augmented. Understanding this building process gives you the power to construct, modify, and analyze any chord you encounter.
The root note is the foundation of every chord and gives the chord its letter name. When you see "C major," C is the root. Above the root, you add a 3rd (which determines major or minor quality) and a 5th (which determines whether the chord is standard, diminished, or augmented). These three notes, the root, 3rd, and 5th, form a triad, and triads are the building blocks of all more complex chords.
On guitar, this interval-based approach is more useful than memorizing chord shapes. When you understand that a major chord is R-3-5 and a minor chord is R-b3-5, you can build any chord from any root on any part of the fretboard. You can also modify existing shapes intelligently: lowering the 3rd of a major chord by one fret turns it into a minor chord, because you are changing the major 3rd to a minor 3rd.
This is the foundation of scale harmonization, where chords are built from scale degrees. Every chord that occurs naturally in a key comes from stacking thirds within the major scale. Understanding this process connects chord theory to scale theory, revealing why certain chords belong together and how to predict the chords in any key.
2 Major and Minor Triads
A major triad consists of a root, a major 3rd (four half steps above the root), and a perfect 5th (seven half steps above the root). The major 3rd gives the chord its bright, happy quality. On guitar, the open C, G, D, A, and E chords you learn as a beginner are all major triads, though they often double some notes across the six strings.
A minor triad consists of a root, a minor 3rd (three half steps above the root), and a perfect 5th (seven half steps, same as major). The only difference between major and minor triads is the 3rd. This one-fret difference on the guitar produces a dramatic change in emotional quality, from bright and resolved to dark and melancholic. The open Am, Em, and Dm chords are minor triads.
Understanding that the 3rd is the "quality-defining" interval opens up the entire fretboard. If you know where the 3rd is in any chord shape, you can switch between major and minor by moving it one fret. In a barre chord rooted on the 6th string, the 3rd is on the 3rd string. Lower it by one fret and the major barre chord becomes minor. This single piece of knowledge lets you derive minor shapes from major shapes anywhere on the neck.
Major vs Minor Triad Construction
C Major Triad:
C (root) + E (major 3rd, 4 half steps) + G (perfect 5th, 7 half steps)
Formula: R - 3 - 5
C Minor Triad:
C (root) + Eb (minor 3rd, 3 half steps) + G (perfect 5th, 7 half steps)
Formula: R - b3 - 5
On Guitar (A string root, 3rd fret = C):
C Major: C Minor:
e|---0--- e|---3---
B|---1--- B|---4---
G|---0--- G|---5---
D|---2--- D|---5---
A|---3--- A|---3---
E|------- E|-------
The only fretted note that changes is the 3rd (E to Eb)
Pro Tip
Practice building major and minor triads on a single string group (e.g., strings 4-3-2) starting from every fret. This strips away the familiar open chord shapes and forces you to hear and visualize the interval structure. Once you can build triads anywhere, chord voicings become creative choices rather than memorized positions.
3 Diminished and Augmented Triads
A diminished triad consists of a root, minor 3rd, and diminished 5th (six half steps above the root, also called a tritone). Both intervals are "minor" or "lowered," which gives the chord an extremely tense, unstable sound. Diminished triads occur naturally as the vii chord in any major key, such as Bdim in the key of C. They function as dominant substitutes and create strong pull toward resolution.
An augmented triad consists of a root, major 3rd, and augmented 5th (eight half steps above the root). The augmented 5th raises the perfect 5th by one half step, creating a symmetrical structure where both intervals from root to 3rd and 3rd to 5th are major thirds. This symmetry gives augmented chords a floating, unresolved quality that sounds neither happy nor sad but rather suspended in harmonic space.
On guitar, diminished triads appear frequently as passing chords and in jazz harmony. The classic diminished chord shape is compact and moveable, repeating every three frets due to its symmetrical construction. Augmented chords are less common but appear in Beatles songs, jazz standards, and any context where a composer wants to create a dreamlike or transitional harmonic moment.
Pro Tip
Both diminished and augmented triads are symmetrical, meaning the same shape repeats at regular intervals up the neck. A diminished triad repeats every 3 frets (minor 3rd), and an augmented triad repeats every 4 frets (major 3rd). This means there are really only four unique diminished triads and four unique augmented triads, just in different inversions. Knowing this simplifies your fretboard mapping enormously.
4 Seventh Chords
Seventh chords add a fourth note on top of a triad by stacking another third. The most common types are major 7th (R-3-5-7), dominant 7th (R-3-5-b7), minor 7th (R-b3-5-b7), minor 7th flat 5 or half-diminished (R-b3-b5-b7), and fully diminished 7th (R-b3-b5-bb7). Each type has a distinct sound and harmonic function that expands your vocabulary far beyond basic triads.
The major 7th chord sounds lush and sophisticated. It serves as the I and IV chord in major key harmony. The dominant 7th chord is the quintessential blues and rock sound, with the tension of the minor 7th against the major 3rd creating a strong drive toward resolution. It naturally occurs as the V chord. The minor 7th chord is warm and mellow, serving as the ii, iii, and vi chords in major keys.
Half-diminished 7th chords (min7b5) appear as the vii chord in major keys and the ii chord in minor keys. They are essential in jazz, where they appear in minor ii-V-i progressions. Fully diminished 7th chords are symmetrical (repeating every 3 frets) and function as chromatic passing chords or dominant substitutes. Each of these chords can be understood through the circle of fifths and their functional roles in harmony.
The Five Main Seventh Chord Types (built on C)
Major 7th (Cmaj7): C - E - G - B (R-3-5-7)
Dominant 7th (C7): C - E - G - Bb (R-3-5-b7)
Minor 7th (Cm7): C - Eb - G - Bb (R-b3-5-b7)
Half-dim (Cm7b5): C - Eb - Gb - Bb (R-b3-b5-b7)
Diminished 7th (Cdim7): C - Eb - Gb - Bbb (R-b3-b5-bb7)
Chord function in C major:
Cmaj7 Dm7 Em7 Fmaj7 G7 Am7 Bm7b5
Imaj7 ii7 iii7 IVmaj7 V7 vi7 vii-7b5
5 Extended Chords: 9ths, 11ths, and 13ths
Extended chords continue stacking thirds beyond the 7th. A 9th chord adds the 9th (which is the same note as the 2nd, one octave higher). An 11th chord adds the 11th (same as the 4th). A 13th chord adds the 13th (same as the 6th). These extensions add color and richness to the basic seventh chord framework, and they are fundamental to jazz, R&B, neo-soul, and sophisticated pop harmony.
On guitar, you cannot always play all the notes of an extended chord because six strings are not enough for seven-note chords. The solution is to omit less essential notes. The root can often be left to the bass player. The 5th is frequently omitted because it adds stability but little color. The notes you keep are the root (or not), the 3rd, the 7th, and the extension itself, as these define the chord's quality and flavor.
Dominant 9th chords (R-3-5-b7-9) are essential for blues, funk, and R&B guitar. The classic "Hendrix chord" (7#9) is a dominant chord with a sharpened 9th that creates a gritty, expressive clash. Minor 9th and major 9th chords add elegance to chord progressions and are used extensively in jazz and neo-soul. The 11th and 13th extensions appear in more advanced voicings, often in Dorian or Mixolydian modal contexts.
Understanding chord extensions as stacked thirds from the scale demystifies complex chord symbols. When you see "Dm11" on a chart, you know it means D minor triad (D-F-A) plus the minor 7th (C), the 9th (E), and the 11th (G). Every note comes from the D Dorian or D Aeolian scale. The chord symbol is just a shorthand for a specific selection of scale tones voiced simultaneously.
6 Suspended and Added Tone Chords
Suspended chords (sus2 and sus4) replace the 3rd with either the 2nd or 4th degree. Since the 3rd defines whether a chord is major or minor, removing it creates an ambiguous, open sound. Sus4 chords (R-4-5) have a tense quality that wants to resolve down to the major 3rd. Sus2 chords (R-2-5) have a more open, modern sound. Both appear constantly in rock, pop, and acoustic guitar music.
Added tone chords include the 3rd alongside the added note. An "add9" chord (R-3-5-9) contains the major triad plus the 9th but without the 7th. This distinguishes it from a full 9th chord, which implies the 7th is present. Add9 chords are brighter and less harmonically complex than full 9th chords, making them popular in pop and rock. The open Cadd9 and Gadd9 shapes are among the most popular acoustic guitar voicings.
Power chords (R-5) technically are not triads because they lack the 3rd entirely. This omission is what makes them work so well with heavy distortion, where the 3rd would create harsh overtones. Power chords are neither major nor minor, which gives them a neutral, aggressive quality that has defined rock and metal guitar since the 1960s. They are the simplest application of interval theory on guitar.
Suspended and Added Tone Chord Formulas
Sus4: R - 4 - 5 (3rd replaced by 4th)
Sus2: R - 2 - 5 (3rd replaced by 2nd)
Add9: R - 3 - 5 - 9 (triad + 9th, no 7th)
Add11: R - 3 - 5 - 11 (triad + 11th, no 7th)
6: R - 3 - 5 - 6 (triad + 6th)
Power: R - 5 (no 3rd)
Common Guitar Voicings:
Csus4 Csus2 Cadd9
e|---1--- e|---0--- e|---0---
B|---1--- B|---1--- B|---3---
G|---0--- G|---0--- G|---0---
D|---3--- D|---3--- D|---2---
A|---3--- A|---3--- A|---3---
E|------- E|------- E|-------
7 Applying Chord Theory on the Fretboard
The real power of chord construction theory on guitar is the ability to create voicings on the fly. When you need a Cmaj9 and do not have a shape memorized, you can build one by finding C, E, B, and D on adjacent strings. Knowing where each interval sits relative to a root note on any string lets you construct any chord from first principles, freeing you from shape-based memorization.
Start by mapping the intervals on the fretboard relative to common root positions. If the root is on the 5th string, the major 3rd is two frets up on the 4th string. The 5th is two frets up from the root on the 3rd string. The minor 7th is one string up and two frets back. These relative positions hold regardless of the root note because the guitar's tuning creates consistent interval relationships across the neck.
A practical exercise is to take a familiar chord shape, identify every note's function (root, 3rd, 5th, 7th), and then modify individual notes to create new chord types. Start with a basic E-shape barre chord, identify the 3rd, and lower it one fret to get minor. Add a note two frets below the root on the same string to get the minor 7th. This incremental modification approach builds a deep understanding of the fretboard's interval architecture.
Pro Tip
Create a chord construction practice routine: pick a random chord symbol from a jazz standard, build it from scratch using interval knowledge, then check your voicing against a chord dictionary. Within weeks, you will be able to voice any chord without looking it up. This skill is invaluable for both jazz comping and creative acoustic arrangements.
Key Takeaways
- All chords are built by stacking intervals (primarily thirds) above a root note
- The 3rd defines major vs minor quality: major 3rd (4 half steps) for major, minor 3rd (3 half steps) for minor
- The four triad types are major (R-3-5), minor (R-b3-5), diminished (R-b3-b5), and augmented (R-3-#5)
- Seventh chords add a 7th to the triad; the five main types are maj7, dom7, min7, min7b5, and dim7
- Extended chords (9th, 11th, 13th) continue stacking thirds; on guitar, omit the 5th and sometimes the root to make them playable
- Suspended chords replace the 3rd with the 2nd or 4th; add chords include the 3rd plus an extra tone without the 7th
- Understanding interval formulas lets you build any chord from any root on any part of the fretboard