Music Theory for Guitar

Lately, I’ve been thinking a lot about the relationship between chords and scales and why certain chords sound good when played in a particular key.

Turns out, every note in a scale has a relative chord. A relative chord is a chord that sounds good with that note as the root note of a scale. But how do we know which chord this is?

Your run-of-the-mill standard chord is made up of the first, third and fifth notes of a scale. For example, in the C scale (C, D, E, F, G, A, B), the C chord is composed of C (1st), E (3rd) and G (5th). Playing these together makes the C major chord:

C major scale fingering

Composition of a C major chord

Composition of a C major chord

So all the other notes in the C scale have their own relative chords. If we play the C major scale starting at D (Dorian Mode), we end up with D (1st), F (3rd) and A (5th) which makes a D minor chord:

D minor chord

But how come playing in Dorian mode created a D minor chord whereas playing in Ionian mode (i.e. starting at C) created a major chord?

This is beacuse of the F note. If you look at the D major scale (D, E, F#, G, A, B, C), the 3rd note is F# (1st is D, and 5th is G). But playing in C major Dorian Mode (starting at D), this produces F.

So the difference between major and minor is a flattened 3rd. D major = D, F#, G and D minor = D, F, G.

There are 7 modes total (8 notes in a scale, but the 8th note is the same as the root, only higher octave):

1. Ionian
2. Dorian
3. Phrygian
4. Lydian
5. Mixolydian
6. Aeolian
7. Locrian

In our C major example, playing out all the modes and finding their 1st, 3rd and 5th notes produces the following progression:

1. Ionian – C major
2. Dorian – D minor
3. Phrygian – E minor
4. Lydian – F major
5. Mixolydian – G major
6. Aeolian – A minor
7. Locrian – B diminished

Download the PDF of the C Major relative chords

Taking away the notes, we can see a pattern for every scale:

Major, Minor, Minor, Major, Major, Minor, Diminished.

Minor Scale

What is a minor scale? A minor scale is simply a major scale played in Aeolian mode. If you look at the notes of A minor:

The A minor scale

Those are the exact same notes in a C major scale, just started at A (Aeolian Mode). The minor scale is 3 half-steps “below” the major scale (a half-step is a chromatic transition between notes, C -> 1/2 step down -> B -> 1/2 step down -> Bb -> 1/2 step down -> A).

Therefore, a minor scale has the following relative chords (same as C, starting at A):

A minor, B diminished, C major, D minor, E minor, F major, G major

Every major scale 3 half-steps down is a minor scale. Some examples:
C major = A minor
E major = D# minor
A major = F# minor

Chord Progressions

The major/minor scale can be found in a vast majority of rock songs, from AC/DC [Shook me all night long: G (I), C (IV), D (V)], Sweet Home Alabama (D, C, G), to country songs like Kenny Chesney’s Come Over (Am, F, C, G), etc. The most common rock three-chord progression is I-IV-V and four-chord progression is I-IV-I-V.

See the list of common chord progressions.

Next up, I’ll explore the harmonic minor scale (minor scale with a sharpened 7th) – the results are very interesting and surprising.

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