Untangling Chord Progressions

Jan09

There have been a few threads on the Forum pages recently on chord progressions, so I thought I’d jot down some thoughts on progressions, and how chords fit together.

Chords are usually labeled with Roman numerals; capital letters mean major chords, lower-case letters means minor. The other chord symbols (+ for augmented, º for diminished, etc.) get added to the Roman numerals. Roman numerals are handy, because they make easy transposition… I-IV-V can be thought of in any key – it takes less work to go from C-F-G to Eb-Ab-Bb if you think in terms of scale degrees. I’ll use Roman numerals throughout this piece.

Harmonizing Scales To Get Chords

Chords in any key are built on the steps of the scale. To start with, let’s look at a harmonized scale in triads (all the examples will be in C):

Example 1

And harmonized to seventh chords:

Example 2

I’ll talk only about major keys here, but all the ideas can be applied to minor keys as well – just use the minor scale notes to create the chords.

Playing through those chords one by one, you’ll see that any chord sounds complete by itself, except the chords built on V (when harmonized as V7) or vii (as either viiº or vii7b5). These two chords have a lot of tension in them, and they want to move, or ‘resolve’ to another chord to sound complete.

Cadences

Chords naturally want to move down by fifths – that is, the root is going to move five steps down the scale. A V7 chord will naturally want to move to a I chord; that’s true of major keys where V7 –> I, and minor keys where V7 –> i. This is the strongest resolution in music, and it’s called the authentic cadence.

G7-C G7-Cm

V7 –> I V7 –> i

Moving down by a fifth (G-C) is the same as moving up by a fourth:

Example 3

so chord movement by fourths is also very common. The change IV –> I gives almost as strong a sense of closure as V7 –> I, and it’s called the plagal cadence. You probably recognize that sound – it’s sometimes called the ‘Amen’ cadence because of its use in church music.

F-C

IV –> I

Since these cadences sound so complete, they are used at the end of chord progressions. Almost all chord progressions will end up on the I chord.

The Natural Harmonic Series

Because chords want to move down by a fifth, we can line them all up in order to create what’s known as the natural harmonic series. This flow will sound very natural to the ear:

Bº Em Am Dm G7 C

viiº –> iii –> vi –> ii –> V –> I

The IV chord can be tacked on to the end, and it will usually go back to I:

Bº Em Am Dm G7 C F C

viiº –> iii –> vi –> ii –> V –> I?IV

Most jazz music is based on the natural harmonic series, with the ii –> V –> I progression being used frequently.

Dm7 G7 Cmaj7

ii –> V –> I

The Blues Progression

Blues music has developed into a standard 12-bar format. Although you can have blues progressions that use other formats, just about all of them will use the I, IV, and V chords in this pattern:

Chord pattern

The V in parenthesis in the last measure is called a ‘turnaround’… if you’re going to do another chorus, the V leads back into the I chord at the start of the progression. The last time through, you stay on the I chord through the final measure.

These two chord progressions, the ii-V-I from jazz, and the I-IV-I-V-IV-I from blues, form the core of most music you hear today. Now let’s start dressing them up…

Chord Extensions

We looked at how chords can be built by harmonizing the major scale in triads and seventh chords – we don’t have to stop there! 9 th , 11 th , and 13 th chords can be substituted as extensions.

Chords get extended by keeping them in the same chord type – for a C chord you can use Cmaj7, Cmaj9; Am can become Am7, Am11… G7 can become G13, G9, etc.

The Secondary Dominant Principle

The V7 chord wants to move down by a fifth, to a I chord. What if we make that a I7 chord instead?

G7 –> C7

V7 –> I7

That change sounds pleasing, because the chord root is moving as an authentic cadence… but it doesn’t sound complete, because the final chord is Domnant. That C7 wants to resolve someplace, and the natural place is a fifth lower:

G7 –> C7 –> F

V7 –> I7 –> IV (in C, or)

II7 –> V7 –> I (in F)

We can string together a whole bunch of 7 th chords, and lead eventually to a final resolution. In the key of C, the D chord is usually minor, but a D7 chord will sound good if we resolve it like this:

C –> D7 –> G7 –> C

I –> II7 –> V7 –> I

The reason this works is that we’ve temporarily moved to the key of G… D7 is the V chord in G. Since G is the V chord in C, we call the D7 the ‘V of V chord’. This temporary key change is called a modulation, and it allows us to use chords outside of the home key:

Key chart

Substitutions

The principles of extension, natural harmonic series, and secondary dominants can be used to substitute chords and dress up a progression. Let’s say the basic chord progression is C-F-G7-C for one measure each:

C F G7 C
| / / / / | / / / / | / / / / | / / / / |

We can plug in a secondary dominant:

C F D7 G7 C
| / / / / | / / / / | / / / / | / / / / |

or turn that G7 measure into a ii-V-I progression:

C F Dm G7 C
| / / / / | / / / / | / / / / | / / / / |

We can add extensions:

C Cmaj7 F Fmaj7 Dm7 G7 C
| / / / / | / / / / | / / / / | / / / / |

And since the authentic cadence can be either V-I or V-i, we can use a secondary dominant to step into any major or minor chord in the progression:

C Cmaj7 F A7 Dm7 G7 C
| / / / / | / / / / | / / / / | / / / / |

In that last example, the A7 is quite a leap from the F, but it’s the V of D (or D minor), which is the V of G… which is the V of C.

Chromatic Steps

Other chords outside the key can be used effectively. Although the introduction of an ‘outside’ chord will initially jar our ears, it’s what you do with it that matters in the end. Chord can be approached by a chromatic half step, either between to chords a step apart (as a passing chord):

C F F# G7 C
| / / / / | / / / / | / / / / | / / / / |

or this:

C C#m7 Dm7 G7 C
| / / / / | / / / / | / / / / | / / / / |

Or we can ‘overshoot’ a chord change, and step down:

Cmaj7 Fmaj7 Ab9 G9 Cmaj7
| / / / / | / / / / | / / / / | / / / / |

Using these substitutions can bring you hundreds of new progressions. If there’s enough interest in this topic, I’ll write another one on the use of altered chords, like E7#9b5.

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About Tom Serb

Tom Serb is a Chicago area guitarist who has been making music professionally since 1978. Over the course of the past twenty-five years he has managed to amuse himself by teaching, writing, performing, producing and composing. He is the author of Music Theory for Guitarists (NoteBoat, Inc., 2003), and a frequent contributor to the Guitar Noise forums.

Comments [2]

  1. thx great info

  2. Whoa I’m finally starting to understand chord progressions. I have a feeling this is going to take some practice and experimentation before it really sinks in … but all of a sudden it doesn’t seem so abstract anymore.

    I’m going to give that blues progression a try.

    -Shane

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