5D Building Chords on Scale Degrees
We saw in the chapter on scales that we can build scales in major, and in the relative minor, with the following scale degree names.
In major:
and in minor:
In the opening page of this chapter, we saw that triads are the fundamental building block of harmony, and that triads can be built above the tonic, subdominant and dominant poles of the scale
We add to this primary group the triad based on the sixth degree of the scale, which can be thought of as the relative tonie (or T-R).
We then assign Roman numerals to these chords, based on their root or bass note. Roman numerals are used to indicate chords as a convenient shorthand, since we use so many Arabic numerals in our music system. When a Roman numeral is employed, we know that it automatically refers to a triad based on a particular scale degree.
When the chords are major, upper case Roman numerals are used to indicate their quality, and when the chords are minor, as in the case of the relative-tonic, lower case Roman numerals are used.
We can now fill in the remaining chords of the scale, labelling those triads by the same names as the scale steps:
Notice that these triads form three distinct groups. I, IV and V are major triads, ii, iii and vi and minor triads. The triad built on the seventh step of the scale is a diminished triad, due to the existence of the diminished fifth between its outer notes, rather than the perfect fifth.
The diminished triad will be dealt with in a subsequent section.
While these chords appear as distinct triads, it is useful to understand their function. In general, think of these chords in these groupings:
- I, IV and V are the primary triads. They form, as we have seen, an essential polarity. They have the function names Tonic (T), Subdominant (S) and Dominant (D), respectively.
- vi is the Relative Tonic (T-R) and thus forms a version of the tonic
triad that contains the submediant tone, the A if we are in C.
- It is common for V to move to I, but it is also common for V to move to vi, as the relative tonic.
- ii is the Relative Subdominant (S-R). (Since IV often moves to V, ii therefore also moves most often to V.)
- iii is the Relative Dominant. (D-R). It serves as a softer version of the V chord. The progression I-iii-vi is a common substitute for I-V-vi.
- vii is the leading tone triad. It is a special case, which we will discuss in the page on dominant seventh chords.
Here then are some common chord progressions, just to give you an idea. In the later sections of this chapter, there will be a few pages that concern the essential chord progressions.
- I—vi—IV—V—I is the classic 50s Rock'n'Roll progression. You may also know it as the "Heart and Soul" progression.
- ii—V—I is a standard chord progression in jazz standards. We will look at this progression in Chapter 6.
- IV—V—vi is considered a deceptive cadence, in that the harmony seems to move towards I, but resolves instead on the relative tonic.
There will be more to say on chord progressions in Chapter 6.
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