Intervals Are Our Friends
As stated earlier, these chords contain a root, a third, a fifth and a seventh. But how can we know which notes can fill these roles at any given time? And are some more important than others? I'm going to conclude this portion of Harmony 101 with the anwers to these questions.
Third floor, sporting goods...
The root, as we already know, is the note within the Major scale that gives the chord its name. That is the starting point as we journey vertically to create the chord. Going up, we skip the next note in the scale and stop on the one after that. That's our third. Depending on which scale degree the root is, the actual interval will be either a minor third (3 half steps) or a major third (4 half steps). Going up two more scale degrees, we stop at the fifth. This interval is called a perfect fifth (7 half steps) except when the root is the vii (seventh) scale degree -- remember that "special chord" I told you about -- the fifth is diminished by one half step.
Two scale degrees past the fifth is the seventh. Here's where terminology can get confusing. In the case of the I or IV, the interval is a major seventh (11 half steps). In all other cases the interval is a minor seventh (10 half steps). This use of "minor seventh" is different from the chord name.
To recap, here are the intervals of each of the seven chords found in the Major scale:
Degree Chord tones Type of Chord
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I Root 3rd 5th 7th Major 7th (Maj7)
ii Root b3rd 5th b7th Minor 7th (Min7)
iii Root b3rd 5th b7th Minor 7th (Min7)
IV Root 3rd 5th 7th Major 7th (Maj7)
V Root 3rd 5th b7th Dominant 7th (7)
vi Root b3rd 5th b7th Minor 7th (Min7)
vii Root b3rd b5th b7th Half Diminished
(Min7b5 or ø)
That's it for now. Next time we'll look at how these chords operate in progressions and different keys. See you then!
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