This unit will be your first introduction of functional accidentals–meaning altered notes that are critical to the function of a chord rather than embellishing non-chord tone accidentals of diatonic harmony. So this marks the beginning of our studies of chromatic harmony. As you read on, remember that all tonal harmony relates back to the function and voice-leading that we established in studying diatonic harmony.
Secondary dominant chords are a logical extension to diatonic progressions and an obvious starting point for studying chromatic harmony, because they are simply an elaboration of circle-of-fifths progressions. Let’s begin by harmonizing the following progression in four-part harmony. Because it is full of root position triads, you will need to use multiple incomplete chords to use smooth voice-leading while avoiding errors.
In Unit 7, we discussed the evolution of the circle-of-fifths progression, and in that process, we saw that the circle-of-fifths progressions are strong because the voice-leading closely mirrors a series of V-I progressions. With that in mind, let’s zoom in on the middle measure of the ii-V-I progression that you completed above. (This will work for any voicing that you chose, but I have inserted the voicing that I used in the next example.) On the staff below, I have isolated the ii and V chords in the first two measures. In the second measure, I have copied all of the voices exactly from the first measure, but I have altered only the key signature to match the tonic of the second chord–in this case, our second chord was the V chord, a G major triad, so I used the key signature for G major without altering any of the voices. Analyze the second measure in G major while taking into account the new key signature. What progression have we created?
As you can see, these two progressions are identical with the exception of one accidental. The ii-V progression in C major has a weaker pull than the V-I progression in G major, but they are functionally similar. Therefore, we could strengthen the ii-V progression in C major by adding one accidental to the ii chord to have it mimic the dominant chord in a secondary key. To try this, take your completed progression from the first example above and alter the one pitch necessary in the ii chord to “borrow” the dominant chord from G major. (I have provided you with my voicing if you deleted yours, but feel free to copy your voices into the appropriate lines of the ABC notation.)
To do this, you only need to raise the third of the ii chord to create a D major triad–the V chord in the key of G major. This creates a temporary V chord instead of a ii chord which you can hear by playing the following example.
In this case, the progression is momentarily acting as if a non-tonic chord–in this case, the V chord–has become the tonic. We call this tonicization. It is the process of borrowing the dominant function from a non-tonic chord’s key to provide emphasis and prolong a chord’s function.
Tonicization is a secondary function. When studying function in diatonic contexts we discussed the primary functions of tonic, dominant, and pre-dominant, as well as tertiary functions such as cadential, passing, pedal, and arpeggiated. Secondary function is yet another category of functions in which the primary functions–i.e. the tonic and dominant relationship–of a second key are used in our original key.
In the example above, the ii chord becomes a major chord once the sharp is added, so it is no longer a ii chord. To denote this in our Roman numerals, we use two Roman numerals separated by a slash: V/V. We read this as “five of five”. In this labeling, the Roman numeral before the backslash is the chord’s function as if it were in the key of the Roman numeral after the slash. In our example above, the D minor chord becomes a D major chord, so it now acts as the V chord in the key of G major: a “five of five”.
One important note, standard practice for secondary function chords allows you to tonicize any chord that is not a diminished triad. This means that viio in major and minor as well as iio in minor should not be tonicized.
Because we label secondary functions in Roman numerals using slashes, students often confuse the function of the slash with leadsheet symbols. In leadsheet symbols, a slash denotes an inversion to the chord by denoting which pitch is in the bass voice, where in Roman numerals, we use inversion figures to denote the bass note. A slash in Roman numerals implies a secondary function and tells you what key is being tonicized. While both systems are useful for theorists, you must be careful not to let the nomenclature mix together.
In our progression above, what would happen if we had decided to use a ii7 chord instead of a ii chord? Try it on the following staff. Start by harmonizing the ii7-V-I progression below while making sure that you resolve your chordal thirds and sevenths correctly. Once you have a voicing that you like, alter the ii7 chord using accidentals to create a V7 in the key of G major – a V7/V (read: “five seven of five”)
When you alter the ii7 chord in the same way that you altered the ii triad to create a secondary dominant, you create a secondary dominant seventh chord–in this case, a V7/V.
There are many possibilities for using these beyond tonicizing V chords, because any major or minor triad can be tonicized by a secondary dominant seventh chord. Instead of altering the ii chord in the above progressions, try altering the vi chord. What chord will it tonicize? Which accidentals will need to be borrowed? What will you call it once you have altered it? We will fully examine these ideas in Unit 15.