From a chord to a progression.
A chord is a stack of thirds. A progression is a stack of chords moving through time. The trick: don't memorize the chords — memorize the formula.
1. What changes when chords move
A single chord is a snapshot. Three notes, frozen. A progression is several chords played in sequence — the harmony moves, and the song moves with it.
Almost every song you know is built on a progression of three to five chords. "96 Tears." "Stand By Me." "Wild Thing." The chords aren't random — they're picked from a small family that belongs to one key.
2. The diatonic family
Every major scale gives you exactly seven chords. One built on each scale degree. We call these the diatonic chords — Greek dia ("through") + tonos ("tone"). Chords through the tones of the scale.
Here's the formula. Start on a scale note, stack a third, stack another third. Whatever notes the scale gives you — that's the chord.
Worked example, key of C major (no sharps, no flats):
| # | Root | Stack | Quality | Roman |
|---|---|---|---|---|
| 1 | C | C – E – G | Major (M3 + m3) | I |
| 2 | D | D – F – A | Minor (m3 + M3) | ii |
| 3 | E | E – G – B | Minor (m3 + M3) | iii |
| 4 | F | F – A – C | Major (M3 + m3) | IV |
| 5 | G | G – B – D | Major (M3 + m3) | V |
| 6 | A | A – C – E | Minor (m3 + M3) | vi |
| 7 | B | B – D – F | Diminished (m3 + m3) | vii° |
The pattern of qualities — major, minor, minor, major, major, minor, dim — is the same in every major key. That's the gift. Learn it once, use it forever.
3. Roman numerals are the formula
Look at the table again. Capital numerals (I, IV, V) are major. Lowercase numerals (ii, iii, vi) are minor. The little circle (vii°) is diminished.
This isn't decoration. It's the whole point. When a musician writes a song using I – IV – V, those three numerals carry both the which (which scale degree) and the what (what quality). Hand a Roman numeral chart to a guitarist in Nashville and they'll play your song in any key you call out — because the formula doesn't care about the key.
4. The I–IV–V
If you only learn one progression, learn this one. I – IV – V. Three chords. All major. It's the spine of blues, country, fifties pop, and most rock and roll.
In the key of G major, that's:
That's I – IV – V in G. Three chords. If you can play those cleanly and switch between them in time, you can play hundreds of songs.
5. The same formula, any key
Here's where the Roman numerals earn their keep. The progression I – IV – V is the formula. The actual chord names depend on the key. Pick a key below and watch the chords change while the formula stays put.
Notice: every key gives you three major chords. Major-major-major. Always. That's the formula doing its job.
6. Quick checks
7. The takeaway
A progression is a sequence of chords. The seven diatonic chords come from one major scale, and their qualities follow a fixed pattern: M m m M M m d. Roman numerals encode that pattern, which means a single progression — like I – IV – V — works in all twelve keys without rewriting anything.
You're not memorizing twelve versions of the progression. You're memorizing one formula and applying it.