The Diatonic Engine
Four chords run most of Western popular music. You've been using them. Let's name them.
- Time
- 90 minutes of study + 45–60 minutes of homework
- You need
- Your guitar in standard tuning for this one, a notebook, and the same two or three of your own DADGAD songs from Week 1
- By the end
- You can build the seven diatonic chords in any major key, name the four progressions that drive most pop music, and translate one of your DADGAD songs into standard tuning chord names
The Major Scale and Its Seven Chords
Take any major scale. Build a triad on each of its seven notes, using only notes from the scale. You get seven chords. These are the diatonic chords of that key — the chords that "belong."
The quality pattern is fixed for every major key:
| Degree | Quality | Roman |
|---|---|---|
| 1 | Major | I |
| 2 | Minor | ii |
| 3 | Minor | iii |
| 4 | Major | IV |
| 5 | Major | V |
| 6 | Minor | vi |
| 7 | Diminished | vii° |
Uppercase = major. Lowercase = minor. The little circle = diminished. Memorize this pattern. Once it's in your head, you can build every diatonic chord in every major key in your head, instantly.
Worked example — D major (the key your DADGAD songs probably live in):
| Degree | Note | Chord |
|---|---|---|
| I | D | D major |
| ii | E | Em |
| iii | F# | F#m |
| IV | G | G major |
| V | A | A major |
| vi | B | Bm |
| vii° | C# | C#dim |
Same pattern in G major: G, Am, Bm, C, D, Em, F#dim. In C major: C, Dm, Em, F, G, Am, Bdim. In A major: A, Bm, C#m, D, E, F#m, G#dim.
One pattern. Twelve keys. Eighty-four chords you now have access to without ever memorizing them individually.
- In any major key, the quality pattern of the seven diatonic triads is: ___, ___, ___, ___, ___, ___, ___.
- In C major, what is the IV chord?
- In G major, what is the V chord?
- In A major, what is the vi chord?
- What is the quality of the chord built on the 7th scale degree of any major key?
Reveal Answers
1. Major, minor, minor, major, major, minor, diminished. 2. F. 3. D. 4. F#m. 5. Diminished.
The Big Four
Of those seven diatonic chords, four do almost all the work in popular music: I, IV, V, and vi. The other three (ii, iii, vii°) show up too, but they're side characters. The big four are the load-bearing walls.
Each one has a job:
- I — home. Resolution. Stability. The chord your ear keeps wanting to return to.
- IV — the lift. Departure from home. Opens up the sky a little. Often used to set up the V.
- V — the tension. Pulls hard back toward I. Contains the leading tone, the note one half-step below the tonic. This is the chord that creates the feeling of about to land.
- vi — the emotional one. The relative minor. Same notes as I and IV largely, but the minor quality gives it weight. The melancholy without leaving the key.
In D major, the big four are: D, G, A, Bm. Look at that list. That is — almost certainly — the chord vocabulary of every DADGAD song you've ever written, just stripped of the sus4 costume.
You haven't been writing modal indie folk. You've been writing pop, with the tuning doing the dressing.
This isn't a criticism. The big four are the big four for a reason — they make sense to the human ear. The point is just to know what you're doing so you can choose when to follow the pattern and when to deviate.
- What are the Roman numerals of the "big four" chords?
- In G major, what are the big four chords (in order: I, IV, V, vi)?
- In C major, what are the big four chords?
- What is the "job" of the V chord, harmonically?
- What is the relative minor of D major, and which Roman numeral is it?
Reveal Answers
1. I, IV, V, vi. 2. G, C, D, Em. 3. C, F, G, Am. 4. To create tension that pulls back to I (dominant function, contains the leading tone). 5. Bm — the vi chord.
Four Progressions, Most of the Last 70 Years
Rearrange the big four and you get the progressions that drive most Western popular music since 1950. Four of them dominate. You have heard them thousands of times.
1. I–V–vi–IV — sometimes called "the axis of awesome" progression after the Australian comedy bit that strung 40 hit songs together over it. In D: D–A–Bm–G. Used by: "Let It Be," "Don't Stop Believin'," "No Woman No Cry," "Someone Like You," "With or Without You" (verse), and an embarrassing number of others.
2. vi–IV–I–V — same chords, different starting point. The "emotional" version because it opens on the minor. In D: Bm–G–D–A. Used by: "Apologize," "Save Tonight," large stretches of modern Adele.
3. I–vi–IV–V — the "50s progression." Doo-wop, early rock, lullabies. In D: D–Bm–G–A. Used by: "Stand By Me," "Earth Angel," "Every Breath You Take."
4. I–IV–V — the three-chord engine. Blues, country, garage rock, punk. In D: D–G–A. Used by: most early rock, most country, most blues, "Twist and Shout," "Wild Thing," roughly the entire AM radio canon.
Some estimate two-thirds of charting pop music can be reduced to one of these four shapes.
The same Roman numeral progression in different keys produces the same emotional arc. I–V–vi–IV in D (D–A–Bm–G) and I–V–vi–IV in G (G–D–Em–C) feel the same. The chords are different. The function is identical. This is what Roman numerals are for — they describe the movement, not the specific pitches.
Two songs by different artists using the same progression sound different because of everything except the chords: melody, rhythm, lyric, production, voice. So if your songs sound like yours, that's where your voice lives. Not in the chords.
- Write the progression I–V–vi–IV in the key of D major (chord names).
- Write the progression vi–IV–I–V in the key of G major.
- Translate the progression I–vi–IV–V from D major to A major.
- What makes two songs that share the same chord progression sound different from each other?
- Why is I–IV–V called the "three-chord" engine?
Reveal Answers
1. D–A–Bm–G. 2. Em–C–G–D. 3. A–F#m–D–E. 4. Everything else: melody, lyrics, rhythm, production, instrumentation, vocal delivery. The chords are only one ingredient. 5. Because it uses only three chords (I, IV, V) — the minimum needed to establish a major key and create harmonic motion.
Catalog Forensics — Your DADGAD Songs, Unmasked
Take one of the DADGAD songs you mapped in Week 1. The one with the clearest progression. Here is the translation protocol:
- Confirm the mode. From Week 1 you should know whether it's D major, Mixolydian, Dorian, or minor. For this exercise, work with major-key songs first (the others have one or two non-diatonic chords that complicate things).
- List the chords as Roman numerals. Strip the "sus" labels — just I, IV, V, vi, etc. The sus4 quality came from the tuning; the underlying chord function is what matters.
- Match against the four classic progressions. Is your song I–V–vi–IV? vi–IV–I–V? I–vi–IV–V? I–IV–V? Or something else?
- Play it in standard tuning with real D, G, A, Bm shapes. No sus4. No drone. Just the bare chord progression.
- Listen. Does it still feel like your song? Or does it sound like a hundred other songs?
If it sounds generic in standard tuning, congratulations — you've located exactly how much of "your sound" was the tuning doing the work versus you doing the writing. That is uncomfortable information and it is also the most useful information you'll get all month.
Do this for two more songs. Look for patterns. Are you writing the same progression in three different songs? Most self-taught songwriters are — and they don't know it until they do this exercise.
Then, the generative half: in standard tuning, write a new 4-chord progression in D or G that is not one of the four classics. Make yourself use ii or iii somewhere. Use the chord patterns you've been avoiding because they don't sit naturally under your DADGAD shapes. This is the first conscious step out of the rut.
Reflection Questions
- How many of your three songs turned out to be a variation of one of the four classic progressions?
- If two or more used the same progression, how would you know the difference between them if the tuning and texture were stripped away?
- What is actually unique about your songs — the harmony, or something else?
- Did the new progression you wrote (with ii or iii) feel awkward at first? Why?
The uncomfortable answer to question 3 is usually: melody, lyric, voice, texture. Not chords. That means your writing voice is real, but it lives outside the harmony. If you want the harmony to also carry your fingerprint, that's what the rest of this curriculum is for.
Before Week 3 — You Should Be Able To
- Recite the diatonic quality pattern (major, minor, minor, major, major, minor, diminished) from memory.
- Build the seven diatonic chords in C, G, D, and A major without looking at notes.
- Name the four classic progressions and play each one in at least two keys in standard tuning.
- Translate at least one of your own DADGAD songs into standard tuning Roman numerals and chord names.
- Articulate where your songs are following the classic patterns and where (if anywhere) they break from them.
Week 3 introduces voice leading — the reason some chord transitions feel inevitable and others feel clunky. It requires that the chord names and functions from this week are already automatic.
The Test Bank
Take this after the homework is done. Score yourself. Answers and scoring at the bottom.
A · The Diatonic Scale (1–10)
- A major scale contains how many notes?
- The quality pattern of the seven diatonic triads in any major key is: ___.
- In C major, the IV chord is ___.
- In G major, the V chord is ___.
- In D major, the vi chord is ___.
- In A major, the ii chord is ___.
- In E major, the I chord is ___.
- The vii° chord is what quality?
- The iii chord in any major key is what quality?
- In F major, the IV chord is ___.
B · The Big Four (11–20)
- The "big four" chords in any major key are the Roman numerals: ___, ___, ___, ___.
- The I chord serves the role of ___.
- The V chord creates ___ that pulls back toward I.
- The vi chord is also known as the ___.
- In D major, the big four chords (in order I, IV, V, vi) are: ___, ___, ___, ___.
- In G major, the big four chords are: ___, ___, ___, ___.
- In C major, the big four chords are: ___, ___, ___, ___.
- In A major, the big four chords are: ___, ___, ___, ___.
- The IV chord is sometimes called the "predominant" or the ___, because it leads away from home.
- The diminished vii° chord is rare in pop because ___.
C · Classic Progressions (21–30)
- The progression I–V–vi–IV in D is: ___ ___ ___ ___.
- The progression vi–IV–I–V in D is: ___ ___ ___ ___.
- The progression I–vi–IV–V in D is: ___ ___ ___ ___.
- The three-chord progression I–IV–V in D is: ___ ___ ___.
- Translate I–V–vi–IV from D to G major: ___ ___ ___ ___.
- Translate I–vi–IV–V from D to A major: ___ ___ ___ ___.
- Translate I–IV–V from D to C major: ___ ___ ___.
- The same Roman numeral progression in different keys produces the same ___.
- The "50s progression" is which Roman numeral sequence?
- Two songs sharing the same chord progression sound different because of: ___ (name at least three factors).
D · Mode and Function (31–40)
- The relative minor of D major is ___.
- The relative minor of G major is ___.
- The relative minor of C major is ___.
- The leading tone of D major is ___.
- In a major key, the leading tone is found in which chord?
- If a song uses C natural in the key of D, it has borrowed from D ___.
- The bVII chord in D Mixolydian is ___ (chord name).
- To translate a Mixolydian song into Roman numerals, the bVII is ___ (a borrowed chord from Mixolydian, sometimes notated as ♭VII).
- In G major, what scale degree is C natural? (Trick question.)
- What chord is built on the 6th scale degree of any major key?
E · Application (41–50)
- A DADGAD song with the chord sequence Dsus4 → Asus4 → Bm → Gsus4 is essentially what Roman numeral progression?
- A song that loops Bm → G → D → A is what Roman numerals in D major?
- To translate a DADGAD song into standard tuning, the first step is ___.
- Your DADGAD song uses Isus → ♭VIIsus → IVsus. In standard D, what chords are these?
- Two of your songs both use I–V–vi–IV. What does that tell you about your harmonic vocabulary?
- To deliberately step outside the four classic progressions, you should use which chord qualities more often?
- If you write a song using only D, G, and A in standard tuning, what classic engine are you running?
- If your DADGAD song collapses into a generic-sounding I–V–vi–IV when played in standard tuning, what does that reveal?
- The point of learning the four classic progressions is not to avoid them, but to ___.
- The single biggest realization most songwriters have from doing this week's homework is ___.
Answer Key
A · The Diatonic Scale
1) Seven. 2) Major, minor, minor, major, major, minor, diminished. 3) F. 4) D. 5) Bm. 6) Bm. 7) E. 8) Diminished. 9) Minor. 10) Bb.
B · The Big Four
11) I, IV, V, vi. 12) Home / tonic / resolution. 13) Tension (dominant function). 14) Relative minor. 15) D, G, A, Bm. 16) G, C, D, Em. 17) C, F, G, Am. 18) A, D, E, F#m. 19) The lift / the subdominant. 20) It's unstable and dissonant — the diminished quality doesn't fit the consonant vocabulary pop music depends on.
C · Classic Progressions
21) D–A–Bm–G. 22) Bm–G–D–A. 23) D–Bm–G–A. 24) D–G–A. 25) G–D–Em–C. 26) A–F#m–D–E. 27) C–F–G. 28) Emotional arc / functional movement / harmonic feel. 29) I–vi–IV–V. 30) Melody, lyrics, rhythm, production, instrumentation, vocal delivery, arrangement, tempo (any three).
D · Mode and Function
31) Bm. 32) Em. 33) Am. 34) C#. 35) The V chord (A major in D — contains C#). 36) Mixolydian. 37) C major. 38) A borrowed chord from Mixolydian (♭VII). 39) It's not in the G major scale at all — G major contains C natural as its 4th scale degree, so C natural is simply the 4th. (The trick was: there's nothing exotic about C natural in G — it's diatonic there.) 40) The vi chord (the relative minor).
E · Application
41) I–V–vi–IV. 42) vi–IV–I–V. 43) Identify the mode and the Roman numeral function of each chord. 44) D, C, G. 45) You're returning to the same harmonic engine across multiple songs — a rut at the writing level, not just the tuning level. 46) The "side characters": ii, iii, and occasionally vii°. 47) The three-chord engine (I–IV–V). 48) That the sus4 ambiguity and drone of DADGAD were carrying the song's distinctiveness — not the underlying harmony. 49) To know when you're using them so you can choose to deviate intentionally. 50) That their "unique" songs are often common progressions in costume — and that their actual voice as a writer lives in melody, lyric, and texture, not in the chord changes themselves.