Chord Theory
Diatonic Chords: A Beginner's Guide to Building Chords from Scales
If you have ever wondered why certain chords seem to belong together in a song while others feel out of place, the answer lies in diatonic harmony. Diatonic chords are the chords that naturally emerge from a scale, and understanding them is one of the most powerful steps you can take as a musician. They explain how songs are built, why common progressions sound satisfying, and how you can start writing your own music with confidence.
What Does “Diatonic” Mean?
The word “diatonic” comes from the Greek diatonikos, meaning “through tones.” In practical terms, diatonic refers to notes, intervals, or chords that belong exclusively to a given key or scale. If you are in the key of C major, the diatonic notes are C, D, E, F, G, A, and B — no sharps, no flats. Any chord built entirely from these seven notes is a diatonic chord in C major.
Chords that include notes from outside the scale are called “chromatic” or “non-diatonic.” They have their place in music, but diatonic chords form the core vocabulary of harmony in any key.
Building Chords by Stacking Thirds
The fundamental technique for constructing diatonic chords is called stacking thirds. Starting on any note of the scale, you skip one note and take the next, then skip another and take the next. This “every other note” pattern produces intervals of a third — either a major third (four half steps) or a minor third (three half steps).
Let us build a triad starting on C in the key of C major:
- Start on C
- Skip D, land on E (a major third above C)
- Skip F, land on G (a minor third above E)
The result is C–E–G, a C major triad. The bottom interval is a major third and the top interval is a minor third. This combination — major third on the bottom, minor third on top — always produces a major chord.
Now build a triad starting on D:
- Start on D
- Skip E, land on F (a minor third above D)
- Skip G, land on A (a major third above F)
The result is D–F–A, a D minor triad. Minor third on the bottom, major third on top — this combination always produces a minor chord.
The Seven Diatonic Triads
When you build a triad on every degree of the major scale, a consistent pattern of chord qualities appears. Here it is in the key of C major:
| Scale Degree | Notes | Chord Name | Quality |
|---|---|---|---|
| 1st | C – E – G | C | Major |
| 2nd | D – F – A | Dm | Minor |
| 3rd | E – G – B | Em | Minor |
| 4th | F – A – C | F | Major |
| 5th | G – B – D | G | Major |
| 6th | A – C – E | Am | Minor |
| 7th | B – D – F | Bdim | Diminished |
Three chord qualities emerge:
- Major (major third + minor third): found on the 1st, 4th, and 5th degrees
- Minor (minor third + major third): found on the 2nd, 3rd, and 6th degrees
- Diminished (minor third + minor third): found on the 7th degree
This pattern is the same in every major key, no exceptions.
The Roman Numeral System
Musicians use Roman numerals to label diatonic chords by their scale degree, making it easy to talk about chord functions regardless of key. The convention is:
- Uppercase Roman numerals for major chords
- Lowercase Roman numerals for minor chords
- A degree symbol (°) for diminished chords
The diatonic chord pattern for any major key is:
I – ii – iii – IV – V – vi – vii°
This notation is universal. When a jazz musician says “play a ii–V–I in B♭,” every musician knows that means Cm–F–B♭, because ii in B♭ major is C minor, V is F major, and I is B♭ major. The Roman numeral system separates the function of a chord from its specific pitch, which is enormously useful for transposition and analysis.
Building Diatonic Triads in Any Key
The beauty of the diatonic system is that once you know the pattern, you can apply it to every major key. Here are several examples:
G major (one sharp: F♯):
| Degree | Chord | Quality |
|---|---|---|
| I | G | Major |
| ii | Am | Minor |
| iii | Bm | Minor |
| IV | C | Major |
| V | D | Major |
| vi | Em | Minor |
| vii° | F♯dim | Diminished |
E♭ major (three flats: B♭, E♭, A♭):
| Degree | Chord | Quality |
|---|---|---|
| I | E♭ | Major |
| ii | Fm | Minor |
| iii | Gm | Minor |
| IV | A♭ | Major |
| V | B♭ | Major |
| vi | Cm | Minor |
| vii° | Ddim | Diminished |
A major (three sharps: F♯, C♯, G♯):
| Degree | Chord | Quality |
|---|---|---|
| I | A | Major |
| ii | Bm | Minor |
| iii | C♯m | Minor |
| IV | D | Major |
| V | E | Major |
| vi | F♯m | Minor |
| vii° | G♯dim | Diminished |
The process is always the same: write out the major scale, then stack thirds on each degree. The quality pattern I–ii–iii–IV–V–vi–vii° takes care of the rest. You can use the Interactive Chord Finder to quickly look up any of these chords and hear how they sound in context.
Why Diatonic Chords Matter
Songwriting
The vast majority of popular songs use mostly diatonic chords. The progression I–V–vi–IV (for example, C–G–Am–F) appears in hundreds of hit songs across genres. Knowing the diatonic chords in your chosen key gives you an instant palette to work from.
Improvisation
When soloing, knowing which chords are diatonic tells you which notes are safe to play at any point. Over a ii–V–I in C major, every note of the C major scale works because all three chords are built from that scale.
Analysis
When you encounter a chord in a song that does not fit the diatonic set, that is a signal worth investigating. It might be a borrowed chord from the parallel minor, a secondary dominant, or a modulation to a new key. You can only spot these interesting harmonic moves if you first know what the “normal” diatonic chords are.
Communication
Roman numerals give musicians a common language. Instead of saying “play C, then A minor, then F, then G,” you can say “play I–vi–IV–V” and any musician can instantly play it in whatever key suits the singer’s range.
Common Diatonic Progressions
Here are some widely used progressions written in Roman numerals, applicable in any key:
- I – IV – V – I — The backbone of rock, blues, folk, and country
- I – V – vi – IV — The “pop” progression heard in countless hits
- ii – V – I — The essential jazz cadence
- I – vi – IV – V — Classic 1950s and doo-wop progression
- vi – IV – I – V — A modern pop and rock favorite
- I – IV – vi – V — Another versatile progression for ballads
Each of these uses only diatonic chords, yet they produce distinctly different moods and feels.
Tips for Practice
Memorize the quality pattern. Say it aloud: “Major, minor, minor, major, major, minor, diminished.” Once this is second nature, you can derive the diatonic chords of any key in seconds.
Build triads in all twelve keys. Write them out by hand on staff paper or use the Interactive Chord Finder to verify your work. Repetition builds fluency.
Analyze songs you love. Pick a favorite song, identify the key, and label each chord with its Roman numeral. You will start seeing the same patterns everywhere.
Experiment on your instrument. Play through all seven diatonic chords in a key, one after another. Listen to how each one sounds relative to the I chord. This ear training is invaluable.
Moving Beyond Triads
Diatonic triads are just the beginning. By stacking one more third on top of each triad, you get seventh chords, which add richness and complexity. The diatonic seventh chord pattern in a major key is:
Imaj7 – ii7 – iii7 – IVmaj7 – V7 – vi7 – viiø7
But that is a topic for another article. For now, master the triads — they are the foundation upon which all more advanced harmony is built.