# AI Wiki - Music - Triads ## Overview A triad is a three-note chord built by stacking two thirds on a root: **root, third, fifth**. Triads are the most common chords in Western music; almost every open guitar chord and most beginner piano chords are triads, sometimes with notes doubled. Everything bigger (sevenths, sixths, add9s) starts from a triad and adds to it. The two thirds can each be major (4 semitones) or minor (3), which gives exactly four triad qualities. See [[AI Wiki - Music - Intervals]] for the interval names. ## The four qualities | Quality | Stack | Formula | Semitones from root | In C | Symbol | |---|---|---|---|---|---| | Major | M3 + m3 | 1 – 3 – 5 | 0, 4, 7 | C E G | C | | Minor | m3 + M3 | 1 – b3 – 5 | 0, 3, 7 | C E♭ G | Cm | | Diminished | m3 + m3 | 1 – b3 – b5 | 0, 3, 6 | C E♭ G♭ | Cdim, C° | | Augmented | M3 + M3 | 1 – 3 – #5 | 0, 4, 8 | C E G♯ | Caug, C+ | - **Major** sounds bright and settled; **minor** darker. The only difference is the third, one semitone apart. The fifth is the same (perfect) in both. - **Diminished** has a diminished fifth (a tritone above the root): tense, unstable, wants to move. - **Augmented** has an augmented fifth: dreamy, unresolved. It is symmetric: three major thirds divide the octave into equal parts, so C+, E+ and G♯+ contain the same three notes. ```chord labels: intervals instrument: piano --- C --- Cm --- Cdim --- Caug ``` ## Triads in a key Build a triad on each note of a [[AI Wiki - Music - Major Scale|major scale]] using only the scale's notes and you get the same pattern in every major key: **major, minor, minor, major, major, minor, diminished**. In Roman numerals: I, ii, iii, IV, V, vi, vii°. Augmented triads don't occur in the major scale. | Key | I | ii | iii | IV | V | vi | vii° | |---|---|---|---|---|---|---|---| | C | C | Dm | Em | F | G | Am | B° | | G | G | Am | Bm | C | D | Em | F♯° | | D | D | Em | F♯m | G | A | Bm | C♯° | | A | A | Bm | C♯m | D | E | F♯m | G♯° | | E | E | F♯m | G♯m | A | B | C♯m | D♯° | I, IV and V (the **primary triads**) carry most of popular music; vi, ii and iii add the minor colours. This is why G, C, D, Em and Am fit together so well on the guitar: they're all triads from the key of G. More in [[AI Wiki - Music - Diatonic Chords and Roman Numerals]] and [[AI Wiki - Music - Common Chord Progressions]]. The diatonic triads of C major on piano (all white keys): ```chord instrument: piano --- C --- Dm --- Em --- F --- G --- Am --- Bdim ``` ## Inversions The **root** of a triad is fixed by the stack of thirds, not by which note is lowest. What is lowest (the **bass**) sets the inversion: - **Root position**: root in the bass (C E G). - **First inversion**: third in the bass (E G C), written C/E. - **Second inversion**: fifth in the bass (G C E), written C/G. Order above the bass and doubled notes don't change the chord's identity. Inversions let chords connect with small hand movements (good voice leading) and make bass lines walk. On piano, the usual right-hand fingerings are 1-3-5 (root position), 1-2-5 (first inversion) and 1-3-5 (second inversion). See [[AI Wiki - Music - Piano Chord Inversions]]. ```chord instrument: piano --- symbol: C pitches: C4 E4 G4 fingering: 1-3-5 title: C (root position) --- symbol: C pitches: E4 G4 C5 fingering: 1-2-5 title: C/E (first inversion) --- symbol: C pitches: G4 C5 E5 fingering: 1-3-5 title: C/G (second inversion) ``` ## On guitar Six strings, three notes: open chords double some triad notes. | Chord | Frets (low E → high e) | Notes sounding | Triad | |---|---|---|---| | C | x32010 | C E G C E | C E G | | G | 320003 | G B D G B G | G B D | | D | xx0232 | D A D F♯ | D F♯ A | | A | x02220 | A E A C♯ E | A C♯ E | | E | 022100 | E B E G♯ B E | E G♯ B | | Am | x02210 | A E A C E | A C E | | Em | 022000 | E B E G B E | E G B | Compare A and Am, or E and Em: one finger moves one fret, and that finger is the third. That one semitone is the whole difference between major and minor. ```chord A x02220 x01230 --- Am x02210 x02310 --- E 022100 023100 --- Em 022000 023000 ``` **Small triad shapes.** Playing only three adjacent strings gives compact, movable triads (no doubled notes). On the top three strings (G, B, e), every major triad has three shapes, one per inversion, that repeat up the neck. They're the backbone of [[AI Wiki - Music - Funk Music|funk]] and [[AI Wiki - Music - Reggae Music|reggae]] rhythm parts and of second-guitar parts that stay out of the way of full chords. G major on the top three strings: ```chord G voicings: all strings: 1-3 inversion: any ``` The same triad shapes are what the [[AI Wiki - Music - CAGED System]] is built from, and they double as [[AI Wiki - Music - Arpeggios]] when played one note at a time. ## Diminished and augmented in real songs They're rarer than major and minor and usually **passing chords**: - **Diminished as a passing chord**: C – C♯dim – Dm walks the bass up chromatically into ii. The vii° of a key (B° in C) contains the upper three notes of G7, so it works as a weaker dominant. - **Augmented as a passing chord**: C – C+ – F (or C – C+ – Am): the raised fifth (G♯) pushes upwards to A, a note of the next chord. In practice, guitarists meet diminished mostly as dim7 chords and augmented as a colour chord in [[AI Wiki - Music - Pop Music|pop]] ballads and [[AI Wiki - Music - Jazz Music|jazz]]; see [[AI Wiki - Music - Seventh Chords]]. ## How to practise 1. **Spell them**: for each root in C, G, D, A, E, say the major, minor, diminished and augmented triad notes aloud. 2. **Harmonise the scale**: play the diatonic triads of G and C up and down on guitar and piano, naming the numeral each time. 3. **Inversions on piano**: play C, F, G in all three inversions, hands separately, then a I–IV–V–I with minimal movement: C – F/C – G/B – C (the top hand barely moves). 4. **Top-three-string triads**: learn the three inversions of G and C on strings G–B–e and move through them along the neck. 5. **By ear**: tell major from minor, then add diminished and augmented. See [[AI Wiki - Music - Chord Quality Recognition]]. ## Common mistakes - Thinking the lowest note is always the root (C/E is still a C chord). - Treating a doubled note as a new chord tone: C E G C E is still a triad. - Forgetting that the key decides which quality each degree gets: the ii chord is minor in every major key. ## Key Points - Triad = root + third + fifth, built from two stacked thirds. - Major 1-3-5 (0-4-7), minor 1-b3-5 (0-3-7), diminished 1-b3-b5 (0-3-6), augmented 1-3-#5 (0-4-8). - Major keys produce I ii iii IV V vi vii°: major, minor, minor, major, major, minor, diminished. - The bass note sets the inversion; doubling and order above it don't change the chord. - Open guitar chords are triads with doubled notes; the major/minor switch is one finger moving one fret. ## Open Questions - **Answered** ([[AI Wiki - Music - Chord Embellishments|Chord Embellishments]]): Which of the top-three-string triad inversions are easiest to switch between for [[AI Wiki - Music - Strumming Patterns|strumming]]? Nearest inversions of chords a third apart (G/B to Em/B, Em/B to C, C to Am/C): one finger moves; same-shape slides are easy but jumpy. - How much of the [[AI Wiki - Music - CAGED System]] falls out naturally from knowing triad inversions? ## References - Triad (music) — Wikipedia: https://en.wikipedia.org/wiki/Triad_(music) - Introduction to Chords — musictheory.net: https://www.musictheory.net/lessons/40 - Triad Inversion — musictheory.net: https://www.musictheory.net/lessons/42 - Diatonic Triads — musictheory.net: https://www.musictheory.net/lessons/43 ## Related - [[AI Wiki - Music - Intervals]] - [[AI Wiki - Music - Seventh Chords]] - [[AI Wiki - Music - Suspended and Added-Tone Chords]] - [[AI Wiki - Music - Arpeggios]] - [[AI Wiki - Music - Diatonic Chords and Roman Numerals]] - [[AI Wiki - Music - Common Chord Progressions]] - [[AI Wiki - Music - Piano Chord Inversions]] - [[AI Wiki - Music - Guitar Open Chords]] - [[AI Wiki - Music - CAGED System]] - [[AI Wiki - Music - Chord Quality Recognition]] - [[AI Wiki - Music - Reading Standard Notation]] - [[AI Wiki - Music - Ear Training]] - [[AI Wiki - Music - Barre Chords]] - [[AI Wiki - Music - Blues Music]] - [[AI Wiki - Music - Circle of Fifths]] - [[AI Wiki - Music - Country Music]] - [[AI Wiki - Music - Left-Hand Accompaniment Patterns]] - [[AI Wiki - Music - Modes]] - [[AI Wiki - Music - Piano Fingering]]