Diatonic harmony is everywhere - from long extended sonatas to melodies such as Happy Birthday, understanding it is essential for mastery on the classical guitar.
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Diatonic harmony: overview
In our last post, we saw how whole and half steps combine to form scales, which have intervals that, when used in certain combinations, generate triads and seventh chords. We are going to take this one step further to look at how these chords work together to create harmonic progressions.
First, let’s explore the harmonies that are built-in to the C major scale. Remember that scale degrees just index the positions of notes 1-7. Let’s build triads on every note of a C major scale (called a “diatonic chord scale.”) We’ll use Roman numerals so as to not confuse these with scale degrees.
Look at the qualities of these triads: three of them are major (I, IV, and V), three of them are minor (ii, iii, and vi), and there’s one diminished triad, the only one that’s neither major nor minor.
Recall the concept of “closely related keys” from Lesson Four on the Circle of Fifths. Any given major key has five other keys that are one accidental away from its key signature (for a total of six keys in one “group”).
For example, the keys closely related to C major (no accidentals) are F major (one flat), G major (one sharp), and each of their relative minors: A minor, D minor, and E minor. Notice that these are the same exact chords that form the diatonic chord scale for C major!
It’s no accident that a diatonic chord scale contains all the keys closely related to the tonic of any key. These chords are generated from the scale itself, so they share many notes in common.
Let’s play a “circle of fifths” progression, only using diatonic fifths instead of perfect fifths.
This way, we remain within C major but get to explore chords via dominant motion.
These voicings are “keyboard style,” meaning there is one bass note in the left hand and three upper notes in the right hand. We’re only playing triads, so one note will be doubled.
Begin practicing this with just the right hand, and add the left hand in when comfortable. If you can master this in C major, then transpose to other keys!
It’s extremely valuable to sing progressions like these. This enhances your ability to listen, and connects the sound, feeling, and theory all in one experience.
For example, to play a circle-of-fifths progression in A♭ major, don’t think of shifting everything from C down a third. Think about the new key’s scale and the resulting sequence of Roman numerals:
Minor chord scales change depending on the kind of minor that you use.
Building chords on natural minor is equivalent to Aeolian, so all the chords will be the same as C major, just renumbered (including a minor V chord on E, which doesn’t have a leading tone.) The presence of the raised seventh (G♯ in A minor) gives us a major third on a V chord.
Building chords with harmonic minor also leads to some strange results, and these chords are rarely used functionally. These are all included below for reference:
What if we build chord scales with seventh chords? We can do this rather quickly by putting our hands in one chord shape (C, E, G, B) and shifting it by steps to the right:
We’ve already looked at the dominant and tonic chords (I and V), but why are they so often found together?
What is it about V that creates closure going to I?
Let’s look at a V7 chord in second inversion, where D is in the bass, followed by a C major triad. Notice how the voices move from chord to chord:
The essence in this chord sequence is the tritone (F to B in the dominant seventh chord) leading to a minor sixth (E to C).
The tritone defines the tension of a dominant seventh chord. Relative to the C major scale, F and B are also one half-step away from other members of the scale, so when they resolve up or down a half-step, we hear pleasing voice leading.
The other notes are somewhat trivial in comparison: D usually resolves down to C (but can resolve up to E,) and G is a common tone to both chords.
We technically don’t even need the G in order to have a satisfying chord progression. If we remove the G we are left with B, D, and F – the notes of a B diminished triad. This chord fulfills the same voice leading as a G7 chord.
In summary, all of the tones of a dominant seventh chord are steps away from or common tones to the notes in the tonic triad. The gravity from V to I is built into the major scale itself.
This is but one example of harmonic function growing from the intervals, the very building blocks we introduced in the first lesson. The tonic to dominant relationship will play a role in the majority of music you play.
A “cadence” is a place where music comes to a sense of rest. V to I is called an authentic cadence. We can also make this cadence resolve to a minor chord, and the tones move very similarly:
The subdominant chord also has a tendency to move toward the tonic, though it’s less strong. The 4th scale degree wants to resolve back down to 3, and 6 down to 5. There is no leading tone (7), and instead 1 is common to both chords. IV to I is called a plagal cadence. Practice different inversions of these chords and note the relationship between the voices. Minor iv to minor i is typically associated with a sad sound, but it’s also a very common progression!
Let’s build our first three-chord progression, the most common one in all of western music: the ii-V-I.
Note that we’re using Roman numerals to signify chords built on each of these scale degrees. In C major, this is D minor (ii), G major (V), and C major (I). Practice the following two-hand voicing in a classical style:
Note that the first chord’s bass note isn’t D, it’s actually F.
This is a first-inversion minor chord, meaning the third is in the bass. The dominant seventh chord also omits the fifth because this note is less important to the sense of resolution.
Practice this progression and transpose it to other keys! You can also play it in minor, remembering that the ii chord becomes diminished.
The following is a jazz variant of a ii-V-I, where all three are seventh chords. In jazz, it isn’t always necessary for the leading tone to resolve to the tonic. In this instance, a major seventh chord on the tonic is much more colorful:
We have finally come far enough to add harmony to “Happy Birthday”.
Let’s use the melody to infer what the chords most likely should be. We are in the key of F major and the first note is C, the fifth scale degree.
The beginning of a piece usually starts with a tonic chord, and that’s exactly what this song does. The D in the melody comes in on a downbeat (scale degree 6,) but this is just an embellishment of the melody.
Feel free to play the melody in any octave!
When the melody moves to scale degree 7, the tonic chord is no longer appropriate.
The leading tone is usually a pretty good indicator that you’re moving to a dominant seventh chord, and that’s just what the song does.
Sometimes if we have a note in the melody, we can exclude it from the harmony in the left hand (leaving the notes G, B♭, and C in the harmony). The main goal of voicing chords is to have good voice leading, or, the smallest possible intervals between successive notes from one chord to the next.
When we say the name of the person whose birthday we are celebrating, we need a new chord: the subdominant!
The seventh scale degree is just a passing tone down to the sixth, a very evocative one! The piece ends with a ii-V-I with one modification. Before the final V is a cadential 6/4.
This is a 6/4 chord (second inversion tonic triad) that is part of an authentic cadence. The bass note is C, meaning the voice leading to the V7 chord will be very smooth.
There are all kinds of other harmonies you can use to make “Happy Birthday” sound unique.
Explore harmony at the keyboard and your instrument – get creative!
Once you’re bored of this piece, move on to other music, improvise and compose things, study scores, and try to understand why great composers made the choices they did.
You have the ability to do all of this now with the skills you’ve gained through this course. Be sure to go at your own pace and remember that there are no rules, only traditions.
Now that we have a locked-in understanding of diatonic harmony, we should be one step closer to having a firm grasp on the music theory we encounter as classical guitarists.
If you’d like to watch the lesson on this topic for free, just click here.
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