Stacking notes into chords, and why they pull on each other.
Ears first. Press both — you will hear the difference long before we name it.
What you’ll learn in this section
- How triads are built by stacking thirds — major, minor and diminished
- Why every key contains the same seven chords in the same pattern
- The three workhorse chords (I, IV, V) and why V pulls home
- How numbered chords explain why so many songs sound alike
- Chord inversions and seventh chords
- The diatonic chords and their functions
- Why V pulls to I, and how function drives cadences
What a chord is
A chord is three or more notes played at the same time. That is the whole idea — nothing harder hiding underneath.
Its mood — bright, dark, or tense — comes entirely from the gaps between the notes.
At Grade 4, only two gaps matter: 4 semitones (a “major third”, the bright one) and 3 semitones (a “minor third”, the darker one).
Why “third”? Because C up to E covers three letter-names (C, D, E) — so it is a “third” whether the gap is three semitones or four.
Every basic three-note chord (called a "triad") is built by stacking two of these thirds on top of a starting note called the "root". The order of the stack determines the character.
Major triad — bright and settled
Major third (4 semitones) on the bottom, then minor third (3 semitones) on top. In C: root C, then up 4 semitones to E, then up 3 semitones to G.
This is C major. The same stack starting on any other note gives that note’s major triad.
Minor triad — darker and more inward
Exactly the reverse: minor third (3 semitones) on the bottom, major third (4 semitones) on top. In C: root C, then up 3 semitones to E♭, then up 4 semitones to G.
This is C minor. One semitone lower in the middle changes the entire character.
Diminished triad — tense and unresolved
Two minor thirds stacked: root, up 3 semitones, up 3 more. In C: C, E♭, G♭. The top note is a semitone lower than in a minor chord, which makes the sound distinctly uneasy. This chord is called "diminished" because the fifth above the root is smaller ("diminished") than usual.
Augmented triad — bright but unsettled
One more completes the set: stack two major thirds — 4 semitones, then 4 more. In C that is C, E, G♯. The fifth is now wider than usual ("augmented"), giving a bright but restless, suspended sound. You meet it far less often than the first three, but it obeys the same logic — every triad is two thirds stacked, and the four combinations (4+3, 3+4, 3+3, 4+4) give the four qualities.
Hear the four side by side
All four qualities on the same root, C — only the middle and top notes shift. Play them in turn and feel each character.
Two distances, glued together
A triad is not three notes to memorise — it is two intervals stacked: a 4-semitone band and a 3-semitone band.
Stack them 4 + 3 and the chord is major; flip to 3 + 4 and it is minor — watch the middle note slide one semitone and hear the light change.
Slide the root anywhere: the stack is rigid, so the chord quality travels with it.
The builder also lets you try inversions: the same three notes, but with the lowest one moved up an octave so a different note sits at the bottom. The chord is still the same chord — root position has the root lowest, first inversion the third lowest, second inversion the fifth lowest. It is a useful thing to hear now; the Advanced course returns to how inversions are labelled and used.
Stack the two thirds yourself
Set each third to major (M3) or minor (m3), then Name it to hear the chord and see which quality you built. The four combinations are the four triad qualities.
Try it: build the triad
Tap any key to put the root there. Switch quality and watch one note slide; switch inversion and watch a note hop up an octave.
Try it: chord builder
Choose a root note and a type. The notes are computed from the interval stack.
You are not memorising chord shapes. You are computing them from two gap sizes. Every chord becomes a calculation, and with practice that calculation becomes a reflex.
Slide the root anywhere and see the chord quality change in real time — major, minor, diminished, inverted.
Every key ships with the same seven chords
Stack a third and another third on each note of the major scale and seven chords fall out — and their qualities are always, in every key, major, minor, minor, major, major, minor, diminished. That invariance is why Roman numerals work: I–V–vi–IV names the positions, and the positions never change. Slide the key and watch the letters change while the pattern refuses to.
Try it: chords in every key
Tap any chord to hear it. The quality badges never move.
Build a progression — then move it
Fill the four slots with numerals, play the loop, then change the key and play it again: the progression survives the move untouched. That is what numerals are for.
Check your understanding
A major triad on G has notes G, B, D. Lower the middle note by one semitone. What kind of chord do you now have?
In any major key: chords I, IV, V = major. Chords ii, iii, vi = minor. Chord vii° = diminished. Same pattern in every key.
Not all seven pull equally
You have just seen that every key contains the same seven chords — I ii iii IV V vi vii° — in the same fixed pattern of qualities. But those seven are not equal partners. Three of them carry most of the musical weight, and they map exactly onto the home-and-away feeling you already know from scale degrees.
Three chords do most of the work
Of those seven, three carry the main weight, and they map exactly onto the home-and-away feeling you already know:
Train your ear
Bright or shadowed? Play the chord, then call it major or minor — the most useful thing an ear learns to do.
That pull from V back to I is the single most important movement in Western music. It is the same leading-note tension you met in the scale degrees, now expressed as a whole chord. When V resolves to I, the journey feels complete.
Why so many songs sound alike
Once chords are numbered, a progression becomes a portable pattern rather than a fixed set of notes. I–IV–V–I is the backbone of countless folk songs, blues, and early rock. I–V–vi–IV underpins a remarkable number of pop songs across decades.
I–IV–V is the engine of the twelve-bar blues and early rock & roll — “Wild Thing”, “La Bamba” and “Twist and Shout” all ride those three chords.
You already know it by ear: the same I–V–vi–IV loop runs under songs as far apart as “Let It Be” and “With or Without You” — four numbers, any key.
The notes change from key to key, but the numbers stay the same. A song in C using I–V–vi–IV plays C–G–Am–F; the same song in G plays G–D–Em–C. Same pattern, different starting point — exactly the logic you saw with scales.
Roman numerals are to chords what the scale pattern is to notes. Learn the progression once as numbers and it works in all twelve keys. This is why musicians can sit down together in any key and play a song none of them rehearsed: they are reading the pattern, not the notes.
Hear all four cadence types back to back, starting from the same phrase. The difference in how they land is immediate.
Type a chord progression and hear a whole rhythm section play it — piano, bass, drums and percussion, locked together in salsa, funk, rock or jazz. The bass and piano both read your chords.
Generate a bass line over a progression in three styles — funk, walking-jazz or rock — built from weighted chord tones and chromatic approaches, then export it as a bass-clef score.
Chords & harmony in Essentials — Major/minor triads, I/IV/V, chord progressions. Revisit →
Root position and inversions
A triad in "root position" has the root as the lowest note. In "first inversion" the third is at the bottom; in "second inversion" the fifth is at the bottom. The notes are the same — only their order from bottom to top changes. Recognising inversions is a Grade 4 expectation.
Try it: chord builder
Choose a root note and a type. The notes are computed from the interval stack.
You are not memorising chord shapes. You are computing them from two gap sizes. Every chord becomes a calculation, and with practice that calculation becomes a reflex.
7th chord = triad + one more third stacked on top. The dominant 7th (V7) is the most important — it pulls powerfully to the tonic.
The diminished 7th chord
Stacking thirds usually gives the familiar triads. Keep stacking minor thirds and you reach one of the most distinctive chords in tonal music: the diminished 7th. It is four notes, each a minor third above the last — for example B–D–F–A♭ — so the whole chord is perfectly symmetrical.
That symmetry gives it two properties worth knowing.
First, it sounds intensely unstable: every interval inside it is tense, so it strains hard to resolve, most often onto a nearby tonic. It frequently does the job of a dominant, pulling powerfully home.
Second, because the stack is identical from any of its notes, one diminished 7th shape can be spelled four different ways and lead to four different keys — which is why composers use it as a pivot to modulate to distant places quickly.
It is the chord of suspense in a great deal of dramatic music.
Labelling inversions: (a), (b) and (c)
In formal music theory, the three positions of a triad are labelled with letters after the Roman numeral:
- I(a) — root position: the root is the lowest note.
- I(b) — first inversion: the third is the lowest note.
- I(c) — second inversion: the fifth is the lowest note.
So “chord V(b) in G major” means a D major triad in first inversion — F♯ at the bottom, then A, then D. The ABRSM uses this labelling system throughout, and being fluent with it means you can identify any chord in any position quickly: look at the lowest note, work out which degree of the scale it is, and that tells you both which chord it is and which inversion.
Check your understanding
A chord has notes B♭, D, F with B♭ at the bottom. The same chord in first inversion would have which note at the bottom?
The diatonic chords and their qualities
Stack thirds on each degree of a major scale, using only notes from that scale, and seven triads emerge with a fixed quality pattern that holds in every key:
Major on I, IV, V; minor on ii, iii, vi; diminished on vii. This is a direct consequence of where the scale's tones and semitones fall, not a convention — the same interval pattern that defines the major scale also fixes which chords come out major and which minor.
Three functions, not seven chords
The seven chords collapse into three functional categories, which is what makes harmony learnable rather than a list of possibilities:
Why V pulls to I
The dominant's pull comes from the leading note (scale degree 7), a semitone below the tonic, which sits inside both V and vii°. That single semitone is the engine of functional harmony: it is what makes V→I feel like an arrival rather than just a change.
From function to cadence
A "cadence" is a functional progression that punctuates a phrase, much as punctuation closes a sentence. The names are just labels for specific functional moves:
Perfect (authentic) cadence: V→I — the full stop, a complete resolution. Plagal cadence: IV→I — the "Amen" ending, gentler. Imperfect (half) cadence: ends on V — a comma, leaving the phrase open. Interrupted (deceptive) cadence: V→vi — the expected resolution is dodged, the music sidesteps home.
The strongest standard approach to the tonic is ii–V–I: subdominant, then dominant, then home. It drives a great deal of jazz and classical harmony alike, because it walks cleanly through all three functions in order.
Why the pattern outlives the key
Because functions are defined by scale degree rather than by absolute pitch, a progression written in Roman numerals is fully portable. I–V–vi–IV is one object that can be instantiated in any of the twelve keys, the way a function in code is one definition called with different arguments.
One construction rule (stack thirds on each degree) produces seven chords; three functions organise them; a handful of cadential moves punctuate phrases. From that small system comes the harmonic structure of an enormous proportion of Western music. The complexity is in the output, not the rules.
Check your understanding
A progression ends V→vi instead of the expected V→I. What is this called?
Perfect cadence (V→I): strongest close. Imperfect (→V): open, questioning. Plagal (IV→I): "Amen" close. Interrupted (V→vi): avoids the expected resolution.