Guitar Secrets Lead Guitar Made Easy

Guitar chord and scale relationships

Recall the word diatonic, this means to be (within the key). The meaning for key can be considered the tonal center or starting point. So, if we wanted to write a song in the key of C major, all the notes in the key of C major would be considered diatonic. For example, the notes in the key of C major are: C D E F G A and B. All these notes are diatonic to the key of C major. Let's say we had the notes Bb, Ab, Eb and Gb. 

These notes would be considered non diatonic to the key of C major. This is because none of these notes can be found in the key of C major. Any note not found in the key of C major would be considered non diatonic. This is true for all the major and minor keys. The notes in the key of G major are: G A B C D E and F#. All these notes are diatonic to the key of G major. It works the same way for all the major keys.

Understanding this information will help when you run into songs that consists of notes that are not diatonic to the key. To tell you the truth, it is very rare to find a song that remains totally diatonic. If a song doesn't remain totally diatonic, then we can find chords that are not diatonic. For Example, the chords in the key of C major are: C Dm Em F G Am and B dim. All of these chords are considered to be diatonic to the key of C major. This goes for major and minor 7 chords and extended chords as well. For Example, any chord that can be formed from the diatonic notes will be considered diatonic to the scale. If you have the Cmaj7 chord, G7, Dm7, Bmin7b5, Fmaj7, Am, Am7 any chord within the key is considered to be diatonic.

Now if we had the Ebm, Gbm, F#, C#, Cm or any chord not found in the key of C major, would be considered non diatonic.

You may have a song based in the key of C major with the following chord progression: C Cm7 Dm7 G7. The Cm7 is not diatonic to the key of C major. So improvising could be a little harder to figure out since the Cm7 chord is not diatonic to the key of C major. We wouldn't want to use the key of C major to improvise over the the Cm7 chord. We may see the following progression: C Ebmaj7 Dm7 G7. The Ebmaj7 chord is not diatonic to the key of C major. We wouldn't want to use the C major scale to improvise over the Ebmaj7 chord.

There are certain situations where it helps to know what scales to use in certain situations. When a song modulates it switches keys and this switch can be momentary. For example, the C Cm7 Dm7 G7 progression modulated, but only momentarily. The Cm7 chord is the only chord that is not diatonic to the key of C major. The C, Dm7 and G7 are all diatonic to the key of C major. So, the Cm7 chord was followed by a chord diatonic to the key of C major.

When a non diatonic minor 7 chord is found in a progression of temporary modulation, you would use the major scale from 1 whole step below the minor 7 chord. Let's take the the C Cm7 Dm7 G7 progression. The major scale 1 whole step below the Cm7 chord would be the key of Bb.

Look at the table below. Locate the key of Bb and notice that Cm is the second note. The Bb would be 1 whole step below the Cm chord. By the way, the second note in the major key can be considered to be the minor 7 scale or Dorian mode. So if you had a chord progression of C Cm7 Dm7 and G7 you would use the key of C major for the C chord, Bb for the Cm7 chord and then back to C major for the Dm7 and G7 chords.

Another example progressions, C Dm Em7 F G7 / C Fmaj7 Em Dm7 Gm7 Fmaj7 G7. You could use the key of C major for all the chords except the Gm7 chord. Look at the table below and find the Gm chord in the second row. You will notice that the Gm is the second chord in the key of F major. So you can use the key of F major for the Gm chord or the G Dorian mode.

In the key of C major and all major keys, the Mediant or 3rd chord in the key is often used and a separation chord for the sub dominant chords. The Sub-dominant chords in the major key are the ii and IV chords. For Example, a progression in the key of C major chord be: C Dm Em F G7 C/ C F Em Dm G7 C. Notice how the Em or Mediant chord in C major is played between the Dm and F and F and Dm chords.

The Mediant and the Sub Mediant chords can be used as the tonic as well. For example, we know that in the key of C major, the Am chord is also the relative minor chord. This chord can be used as the tonic chord for song construction. For example, we could have a progression in the key of Am with the following chords. Am, F G/ Am Dm Em F G. The song is now based in the key of Am and the Am chord is the home or tonic chord.  Am F G/ Em F G/ Em Dm G/ Am F and G.

The Mediant chord can also be used as the tonic. In the key of C major, the Em chord would represent the Mediant chord and the Phrygian mode. Em G Am/ E G A/ Em G Am. Notice that the A chord is not diatonic to the key of C major. We learned what scale to use when we find a minor 7 chord that is not diatonic earlier. But, now what do we do when we find a major chord that is not diatonic to the key we wrote the song in. For this example, we have used the Em G A progression and the A chord is not diatonic to the key of C major. Since the A is not diatonic, what we have done was modulated to a different key. But, we have also only modulated temporarily, since we went back to the Am chord which is diatonic. 

Another important factor to this is the A chord does have a diatonic root to the key of C major. The notes in the Am chord are, A C and E. The notes in the A chord are A C# and E. So the A note or root note in the A chord is diatonic. So, if we have a major chord that is NOT diatonic, but has a diatonic root we use the major scale of the non diatonic chord. In this instance we would use the A major scale.

Say you run into a progression with a major chord that is not diatonic and has a root note that is also not diatonic to the key you are in? Lets stay in the key of C major. C Dm Em F G7 C/ C Dm Eb F G7 C. Notice that the Eb is not diatonic to the key of C major and its root note Eb is not diatonic either. For example, the notes in the Eb chord are Eb G and Bb. The Eb is not diatonic to the key of C major, so we need to figure out what scale to use for that chord. Any time you have a major chord that modulates temporarily to another key with a non diatonic root, it wants to sound like the IV chord of its diatonic scale. Look at the table below and find the Eb in the IV row 4th row. You would use the scale from the 5th chordal degree. For example, the notes in the Eb chord are Eb G and Bb. You could use the Eb Locrian mode or the key of Bb. Bb is the 5th chordal degree of the Eb chord.

Now lets say you run into a progression with a non diatonic dominant 7 chord with a non diatonic root. We know that the dominant 7th chord is the V chord in the major key. For example, the G chord would be the dominant 7th chord in the key of C major. The D chord would be the dominant 7th chord in the key of G major. Look at the table below and find each of those dominant chords. They will be under the Mixolydian mode. 

Anytime you have a non diatonic 7th chord with a non diatonic root it wants to sound like a bVII7 chord in the key of the lowered seventh degree. For example in the key of C major. C Dm Em F G7 C/ C/ Eb7 Am7 Dm Em F G7 C.

Notice that the (Eb7 dominant 7th) chord is not diatonic to the key of C major, it also has a non diatonic root note. We would use the melodic minor scale of the chords 5th chordal degree. For this example the notes in the Eb7 chord are Eb G Bb and D. Bb is the 5th note in this chord. We could use Bb melodic minor to play over the Eb7 chord.

Notice that the (Eb7 dominant 7th) chord is not diatonic to the key of C major, it also has a non diatonic root note. We would use the melodic minor scale of the chords 5th chordal degree. For this example the notes in the Eb7 chord are Eb G Bb and D. Bb is the 5th note in this chord. We could use Bb melodic minor to play over the Eb7 chord.