3. Roman Numerals — so the pattern transfers to any key
Because the major/minor/diminished pattern above is always the same shape, musicians label the 7 chords with roman numerals instead of note names. Capital = major, lowercase = minor, lowercase with ° = diminished:
I – ii – iii – IV – V – vi – vii°
This is the actual payoff: once you know “I–V–vi–IV” as a pattern of numbers, you can play it in any key by just plugging in that key’s chords. Here’s a cheat sheet for the most common keyboard/guitar keys:
| 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 | Bb | C | Dm | Edim |
| Bb | Bb | Cm | Dm | Eb | F | Gm | Adim |
| Eb | Eb | Fm | Gm | Ab | Bb | Cm | Ddim |
Try it: pick your favorite key from the table and play I, then IV, then V, back and forth. Notice how strongly V wants to pull back to I.
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