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Music Theory:

7th Chords Extensions



If we add a fourth note to the chords we examined in the last chapter, we can find all the 7th chords we can build over the notes of the Major scale.

 

Adding B to the C Major chord on the first degree gives us a C Major Seventh chord that we can write as C Maj or C7+ and even CΔ on a chord chart. We can consider the 5 and a half Tone interval from the root that makes up a major seventh interval or we can move one half-tone down from the octave, which can help us visualize the chord on the fretboard.



The chord on the 4th degree is exactly the same, in this case, we add E to an F Major chord to get an F Maj.

For the chords on the second, third and sixth degree, we add a minor seventh to minor chords and we will call them minor 7th chords (D-7 or Dm7, for example). This could be a bit confusing, the ‘minor’ in the chords name refers to the minor third interval of the chord (that makes it a minor chord) while ‘7’ indicates a minor 7th.

 


You can have a Major chord with a major 7th (C7+) but you can also have a major chord with a minor 7th, like the one we can find on the fifth degree of the scale, in this case, G Dominant 7 or G7 in short. We saw in the Mini-course that the minor 7th in a chord’s name is called just ‘7’.

Like we did for the minor 7th, we can consider the 5 Tone interval from the root or use the more practical approach of moving the octave (a 6 Tone interval) back a whole tone.



 

In the last chapter, we learned that the chord built on the seventh degree is a peculiar chord with a diminished fifth. Adding a minor seventh (A over the Bdim Triad, in this case) will give us a Minor 7th Flat 5 chord, also known as the Half-diminished chord or BØ in our example.




Now we can go back to the Major scale and see how adding the 7th to the chords has revealed some very interesting aspects of what we call ‘Scale Harmonization’.



There is only one Dominant 7th chord and it’s on the fifth degree so when we find a 7th chord we know what the scale (and key) is: an A7 would point to a D Major scale while an F#7 would belong to B Major.

We don’t use the term Dominant by chance, it’s the most important chord on the scale and you can hear how it ‘wants’ to go back to the chord built on the first degree, your ear expects the movement from one chord to the other, what we call a Cadence.

We can also give a name to all the degrees in the scale: obviously, the first is the Tonic and the fifth is called Dominant while the fourth is the Subdominant.



We don’t have to learn all the names, a lot of times we can refer to the degrees and relative chords with their Roman numeral, like II - V - I, when we describe a chord progression or a Cadence. It’s also common to use lower case for minor chords: ii - V.

A Cadence generally refers to a progression of chords that lead back to the Tonic and the most important, the ‘Authentic Cadence’ is the movement from V(7) to I.

We can explain the ‘attraction’ of the V to the I if we examine the intervals in the scale, in particular, the halftone intervals between III and IV and VII and VIII: try playing F followed by E and then B followed by C and then F and G together followed by E and C together.

Can you hear how those halftones produce a sense of tension and release that guide you to the second set of notes? What chords in the scale contain those noes?

I guessed it, G7 (F and B) and Major (C and E), V to I.

There are many types of cadences like ii - V - I or IV - V - I and they don’t necessarily need to include the V or even to finish on I, they’re just ways of expressing the balance of tension and release that make musical compositions interesting.

Extending the chords to sevenths generated more chord types but there’s still more missing from the list: are they generated by different scales?

We’ll try to answer that question in the next chapter.

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