Diatonic chords & functional harmony
A whole ensemble of chords grows from a single scale: stack thirds on every degree and you get seven triads that all belong to the same key. They are the raw material of any accompaniment – and the foundation for cadences.
How one scale becomes seven chords
Take a major scale and stand on any of its degrees. Stack two thirds from there – skipping every other scale note – and you build a triad made only of scale tones. Repeat that on each of the seven degrees and you get seven chords guaranteed to fit together, because they all draw on the same pool of notes.
The elegant part: the quality of each chord (major, minor or diminished) falls out automatically from the spacing of the scale. Nothing to memorise – you read it off the stack.
The seven degrees in major
In C major (all natural notes, no sharps or flats) you get these seven triads. The colour already hints at the later function: tonic group gold, subdominant group blue, dominant group green.
Thirds stacked on every degree of C major – root at the bottom, third and fifth above.
| Degree | Chord | Notes | Quality |
|---|---|---|---|
| I | C | C–E–G | major |
| ii | Dm | D–F–A | minor |
| iii | Em | E–G–B | minor |
| IV | F | F–A–C | major |
| V | G | G–B–D | major |
| vi | Am | A–C–E | minor |
| vii° | B° | B–D–F | diminished |
The seventh degree is the diminished B°. The order major–minor–minor–major–major–minor–diminished holds in every major key; only the note names change. Listen to the seven chords one by one:
The seven degrees in minor
In minor the pattern shifts, because the half steps sit in different places. In A minor (natural, also with no sharps or flats – the relative of C major) stacking thirds gives:
A minor (natural): a different order of qualities than major.
| Degree | Chord | Notes | Quality |
|---|---|---|---|
| i | Am | A–C–E | minor |
| ii° | B° | B–D–F | diminished |
| III | C | C–E–G | major |
| iv | Dm | D–F–A | minor |
| v | Em | E–G–B | minor |
| VI | F | F–A–C | major |
| VII | G | G–B–D | major |
Tonic, subdominant, dominant
Not every degree carries equal weight. Three primary functions hold harmony together:
- Tonic (T) – degree I: home, the point of rest. Here the music feels “arrived”.
- Subdominant (S) – degree IV: leads away from the tonic and opens up space.
- Dominant (D) – degree V: builds tension and pushes back to the tonic – especially strong as a seventh chord (V7).
This basic motion T–S–D–T (in numerals I–IV–V–I) is the seed of almost every cadence – more on that in the next step.
When one degree stands in for another
The remaining degrees are not filler – they act as substitutes for the three primary functions. Because each shares two notes with its primary, it can take over that role while adding a softer colour:
- The submediant vi (Am) is the classic tonic substitute – the relative minor of the tonic. The move V–vi instead of V–I is the deceptive cadence.
- The supertonic ii (Dm) substitutes for the subdominant. The progression ii–V–I is everywhere in jazz.
- The mediant iii (Em) sits close to the tonic and colours it.
This substitution principle is the same everywhere: German theory calls vi the Tonikaparallele (Tp), Spanish theory the relativo. The idea stays identical – only the label changes.
Roman-numeral analysis
Roman numerals are an international shorthand that works independently of the key. Read them like this:
- Upper-case (I, IV, V) = major triad.
- Lower-case (ii, iii, vi) = minor triad.
- ° after the numeral (vii°) = diminished triad.
The big advantage: I–V–vi–IV means the same musical event in any key. In C major that is C–G–Am–F, in G major G–D–Em–C – same function, same effect. Think in numerals and you transpose effortlessly and recognise patterns again and again.
FAQ on diatonic chords
Why is the second degree minor and not major?
Because the scale places its half steps at fixed spots. On the second degree (D–F–A) the lower interval is a minor third – that makes a minor triad. The quality of every degree is not arbitrary; it follows from the scale’s structure.
What does the little ° on vii° mean?
It marks a diminished triad – two minor thirds stacked, with a diminished fifth. It sounds tense and unstable and calls for resolution, usually to the tonic.
Why does minor need a raised seventh degree?
Natural minor has no leading tone – the half step just below the tonic that pulls so strongly “home”. Raise the seventh degree (in A minor, G to G♯) and you get harmonic minor: the fifth degree becomes E major and can close as a true dominant.
Do I have to memorise all seven degrees?
No. Once you understand the building principle (root + two stacked thirds from the scale), you can derive every degree yourself. The most common ones – I, IV, V, vi – settle in over time on their own.