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<h1>Chord Progressions</h1>
<p>A chord progression is a sequence of chords that creates harmonic motion. The choice of progression shapes the emotional feel of music more than almost anything else — tempo, instrumentation, and arrangement all dress the song, but the chord changes are the skeleton. Certain progressions have become so common they're essentially part of a shared musical vocabulary.</p>

<h2>The Diatonic Chords</h2>
<p>Build a chord on each note of the major scale using only the notes of that scale. In C major:</p>

<table>
  <thead><tr><th>Numeral</th><th>Chord (C major)</th><th>Quality</th><th>Function</th></tr></thead>
  <tbody>
    <tr><td>I</td><td>Cmaj7</td><td>Major 7th</td><td>Tonic — home, resolved</td></tr>
    <tr><td>ii</td><td>Dm7</td><td>Minor 7th</td><td>Pre-dominant — movement away from tonic</td></tr>
    <tr><td>iii</td><td>Em7</td><td>Minor 7th</td><td>Tonic substitute — shares notes with I</td></tr>
    <tr><td>IV</td><td>Fmaj7</td><td>Major 7th</td><td>Subdominant — classic contrast</td></tr>
    <tr><td>V</td><td>G7</td><td>Dominant 7th</td><td>Dominant — strongest pull to I</td></tr>
    <tr><td>vi</td><td>Am7</td><td>Minor 7th</td><td>Relative minor — tonic-like quality</td></tr>
    <tr><td>vii°</td><td>Bm7♭5</td><td>Half-diminished</td><td>Dominant function, rarely used as is</td></tr>
  </tbody>
</table>

<p>Roman numerals uppercase for major chords, lowercase for minor. The dominant (V) contains the tritone between its 3rd and 7th (B and F in G7) — the strongest possible pull toward the tonic.</p>

<h2>ii–V–I: The Jazz Engine</h2>
<p>The most important three-chord progression in jazz. Nearly every standard contains ii-V-I sequences — recognising and knowing how to play through them is the foundation of jazz vocabulary:</p>
<pre>
In C major: Dm7 → G7 → Cmaj7
In F major: Gm7 → C7 → Fmaj7
In B♭ major: Cm7 → F7 → B♭maj7
In A major: Bm7 → E7 → Amaj7
In Eb major: Fm7 → B♭7 → E♭maj7
</pre>

<table>
  <thead><tr><th>Chord in ii-V-I</th><th>Roman numeral</th><th>Function</th><th>Common scales</th></tr></thead>
  <tbody>
    <tr><td>Dm7 (in C)</td><td>ii</td><td>Pre-dominant — sets up tension</td><td>Dorian, scales of parent major key</td></tr>
    <tr><td>G7 (in C)</td><td>V</td><td>Dominant — maximum tension</td><td>Mixolydian, bebop dominant, altered</td></tr>
    <tr><td>Cmaj7 (in C)</td><td>I</td><td>Tonic — resolution</td><td>Ionian, Lydian, major bebop</td></tr>
  </tbody>
</table>

<h2>I–IV–V: The Vernacular</h2>
<pre>
The backbone of blues, rock, country, and folk.
Three chords → hundreds of songs.

In C: C — F — G   (Cmaj7, Fmaj7, G7 in jazz; C, F, G in rock)
In G: G — C — D
In A: A — D — E
In E: E — A — B

12-bar blues in A (I7, IV7, V7 = dominant sevenths throughout):
A7 | A7 | A7 | A7 |
D7 | D7 | A7 | A7 |
E7 | D7 | A7 | E7 |
</pre>

<h2>I–V–vi–IV: The Pop Rotation</h2>
<pre>
In C: C — G — Am — F
In G: G — D — Em — C
In D: D — A — Bm — G
In E: E — B — C#m — A

Famously demonstrated to underlie dozens of hit songs:
"No Woman No Cry," "Let Her Go," "Let It Be," "With or Without You,"
"Someone Like You," "Poker Face" — same four chords, different arrangements.
</pre>

<h2>I–IV–vi–V and Variations</h2>
<pre>
The same four chords rearranged create different emotional flavours:

I–V–vi–IV (standard pop): resolved → motion → darker → lift
vi–IV–I–V (start on minor): darker start, more introspective
IV–I–V–vi: starts on the lift chord
vi–IV–V–I: traditional resolution at the end
</pre>

<h2>Common Progressions Reference</h2>

<table>
  <thead><tr><th>Name</th><th>Numerals</th><th>Example (C major)</th><th>Genre</th></tr></thead>
  <tbody>
    <tr><td>I–IV–V</td><td>I IV V</td><td>C F G</td><td>Blues, rock, country, folk</td></tr>
    <tr><td>ii–V–I</td><td>ii V I</td><td>Dm7 G7 Cmaj7</td><td>Jazz (everywhere)</td></tr>
    <tr><td>Pop 4-chord</td><td>I V vi IV</td><td>C G Am F</td><td>Pop, rock, worship music</td></tr>
    <tr><td>50s progression</td><td>I vi IV V</td><td>C Am F G</td><td>Doo-wop, 1950s pop</td></tr>
    <tr><td>Minor i–♭VII–♭VI–♭VII</td><td>i ♭VII ♭VI ♭VII</td><td>Am G F G</td><td>Rock, pop-rock</td></tr>
    <tr><td>Andalusian cadence</td><td>i ♭VII ♭VI V</td><td>Am G F E7</td><td>Flamenco, Spanish guitar</td></tr>
    <tr><td>Pachelbel Canon</td><td>I V vi iii IV I IV V</td><td>C G Am Em F C F G</td><td>Classical, pop (widely quoted)</td></tr>
    <tr><td>Rhythm changes (A section)</td><td>I VI ii V</td><td>B♭ G7 Cm7 F7</td><td>Jazz (Gershwin era standards)</td></tr>
    <tr><td>Minor ii°–V–i</td><td>ii° V7 i</td><td>Bm7♭5 E7 Am</td><td>Jazz minor key, classical cadences</td></tr>
  </tbody>
</table>

<h2>Secondary Dominants</h2>
<p>Any diatonic chord can be preceded by its own dominant seventh chord — a chord borrowed from outside the key that creates a temporary tonicisation:</p>
<pre>
V/V (five of five) → V → I
In C: D7 → G7 → Cmaj7
  D7 is the dominant of G — the D7 makes G feel like a temporary tonic.

V/ii → ii:  A7 → Dm7      (A7 is the dominant of Dm)
V/IV → IV:  C7 → Fmaj7    (C7 is the dominant of F)
V/vi → vi:  E7 → Am7      (E7 is the dominant of Am)
</pre>

<h2>Modal Interchange (Borrowing)</h2>
<p>Borrow chords from the parallel minor to add dark colour in a major key context:</p>
<pre>
In C major, borrowed from C minor:
  iv (Fm)   — minor subdominant. Dark, poignant. "Let It Be" uses Fm before C.
  ♭VII (B♭) — borrowed major chord. Rock/modal feel.
  ♭VI (A♭)  — dramatic. "In My Life" uses ♭VI-♭VII-I.
  ♭III (E♭) — borrowed, gives a flat-key lift.
</pre>

<h2>References</h2>
<ul>
  <li>Levine — <em>The Jazz Theory Book</em></li>
  <li>Rawlins &amp; Bahha — <em>Jazzology</em></li>
  <li><a href="https://www.hooktheory.com/theorytab" target="_blank" rel="noopener">Hooktheory — chord progressions in real songs ↗</a></li>
</ul>
