Stop 4 of 6
Harmonising the major scale
The seven chords of a key and Roman numerals.
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Stop 4 of 6
The seven chords of a key and Roman numerals.
Why do C, Am, F and G sound so good together, while C next to F♯ sounds so strange? The answer lies in the scale. At this stop you build the seven chords that “live” in a key, learn to name them with Roman numerals and discover that the same pattern repeats in every key. It is like being handed the city’s street map.
Listen to the C major scale. Seven notes, all white keys on the piano:
Now do what you learned at the previous stop: on every note of the scale, stack two thirds, but using only notes from the scale. On C you get C–E–G. On D, D–F–A. And so on up to the seventh degree.
The result is the : seven chords that share the same seven notes. These chords are : they belong to the key. That is why they sound like a family.
Analyse each triad with what you already know (look at the thirds):
| Degree | Notes | Thirds | Type | Chord | Numeral |
|---|---|---|---|---|---|
| 1 | C E G | M3 + m3 | major | C | I |
| 2 | D F A | m3 + M3 | minor | Dm | ii |
| 3 | E G B | m3 + M3 | minor | Em | iii |
| 4 | F A C | M3 + m3 | major | F | IV |
| 5 | G B D | M3 + m3 | major | G | V |
| 6 | A C E | m3 + M3 | minor | Am | vi |
| 7 | B D F | m3 + m3 | diminished | Bdim | vii° |
Play them on guitar, one after another. You already know these chords; only Bdim is new:
Major · minor · minor · Major · Major · minor · diminished
Roman numerals tell you which degree the chord sits on, and their form tells you what type it is:
So “ii” reads “two minor” and you don’t need to write “m”. The big advantage: a Roman numeral does not depend on the key. “I – vi – IV – V” describes the same progression in any key.
Listen to a very common progression with two minor chords:
Because every major scale has the same formula of whole and half steps, every harmonised scale has the same quality pattern. Only the names change:
| Key | I | ii | iii | IV | V | vi | vii° |
|---|---|---|---|---|---|---|---|
| C | C | Dm | Em | F | G | Am | Bdim |
| G | G | Am | Bm | C | D | Em | F♯dim |
| D | D | Em | F♯m | G | A | Bm | C♯dim |
| A | A | Bm | C♯m | D | E | F♯m | G♯dim |
| E | E | F♯m | G♯m | A | B | C♯m | D♯dim |
| F | F | Gm | Am | B♭ | C | Dm | Edim |
To build any key you don’t need to memorise the table: write out the scale (with its ) and apply the pattern. In G major the scale is G A B C D E F♯, so the seventh chord is F♯dim.
Listen to the same I – vi – IV – V progression in three keys. It sounds just as “familiar”, only higher or lower:
On guitar you can play the harmonised scale as triads on strings 3-2-1, climbing the neck. Every shape uses only notes from C major; see how the pattern changes with each chord type:
Every shape has the chord’s fifth on string 3. The first one (G, C, E) is the top of your open C chord.
What about songs in a minor key? They use the same seven chords, but with a different centre. The of C major is A minor: start counting from the sixth degree and the pattern becomes:
| i | ii° | III | iv | v | VI | VII |
|---|---|---|---|---|---|---|
| Am | Bdim | C | Dm | Em | F | G |
Notice how the feeling changes: with the same four chords as before, “home” is now Am and everything sounds darker.
In the natural minor key, the fifth chord is minor (Em in A minor) and it has no note that “pulls” towards the tonic. That is why many songs raise its third (G → G♯) and use E or E7: this brings back the tension of the dominant. That altered note gives rise to the harmonic minor scale, which you will explore at a later stage.
You will often be handed a list of chords (from a song, a jam, a bandmate) with nobody telling you the key. With this stop’s pattern you can work it out in seconds. Listen to this original progression:
The method has three steps:
Check that everything fits: Em is vi in G major, so the progression is vi – IV – I – V. Notice that step 2 doesn’t need I to appear at all: with just Am, F and G you still land on C major.
On the guitar, step 3 has a shortcut. If you play V as a barre chord rooted on string 6, the root of I is at the same fret, one string higher, and the root of IV is two frets lower on string 6:
String 6, Fret 8: C3 · 4 · Tension
With very few chords, the answer may not be unique. C and G on their own fit both C major (I and V) and G major (IV and I). Then you need one more chord or, better still, your ear.
Play one chord per bar (four downstrokes) and say its numeral on beat one: “one”, “two minor”, “three minor”… Then come back down. Use the backing as a guide.
Goal: Play the seven chords of C major up and down, saying each Roman numeral without stopping, at 70 BPM.
Goal: Play I – vi – IV – V in C, G and D without looking at the table, at 80 BPM.
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