As a student of music theory, it's only logical to start learning about diatonic harmony, both major and minor harmonies. As with any set of guidelines, however, composers found ways around the rules and started to add other chords to the canon of harmony to give greater variety.

Diatonic harmony supports diatonic melodic writing. How do you deal with melodies that contain notes outside the scales? Also, the chord ladder seems to be something you can't easily escape. How do you create interesting progressions that don't simply follow the ladder from end to end? You have already learned that the dominant chord is the basic end of the progression. When you reach that chord, your options are either to cadence and begin a new phrase or to resolve it in some deceptive way. Composers over the course of music history have sought ways to prolong the amount of time it takes to get to the dominant chord. With diatonic harmony, there is only so much that you can do. By providing some additional chords in extended harmony—more specifically, secondary chords—composers could keep the ball in the air a bit longer.

Secondary Chords

A secondary chord is a simple concept: Take any chord in the diatonic scale and precede it with a related chord that is outside the diatonic scale, adding a bit of color and an extra side step in the harmonic picture.

Secondary chords come in two flavors: dominant and diminished. Secondary chords can be used with fully diatonic melodies, adding more richness to already functional, melodic writing. Since dominant and diminished chords are essentially substitutes for each other, you should know why a secondary chord works in any setting.

Secondary Dominant Chords

Dominant chords are typically the V chord of a key and they have a very strong tendency to resolve up a perfect fourth or down a perfect fifth (you'll arrive at the same note) to a tonic I chord. You also know that they are so strong as to define keys by themselves. If you moved the V chord temporarily, to precede another chord in the key, would it work?

The answer is yes. A secondary dominant is a simple action that places a temporary dominant chord a fifth away from any chord in the key. Think of it as a harmonic detour.

Now set up an example. Use the IV chord as the target chord. You want to precede the IV chord with a dominant chord. In the key of C major, IV is F major, and F's dominant chord (a perfect fifth away) is C7. You can see the progression in FIGURE 12.1.

Now, add the secondary dominant to IV in the progression, and you get the progression in FIGURE 12.2.

There are two things to discuss here. First, the additional dominant chord adds a great flavor to an otherwise “stock” progression. Think of the other chords that could have preceded IV; few have the flavor of the secondary dominant. Second, what do you call this chord? In the progression, there is a temporary question mark in place. The chord is C7, so you could call it a I7chord, but that would miss the relationship between the secondary chord and its destination. Instead, you would call that chord V7/IV, or “five of four.” The word of is depicted as a slash and shows clearly that you are adding a chord that is related to the IV chord, instantly resolving to the proper destination: IV.

FIGURE 12.3 shows the proper naming for the progression using Roman numerals.

It is perfectly clear what the function of the nondiatonic C7 chord is in the progression. You could easily realize this progression (write one yourself) in another key simply using the Roman numerals.

Secondary Chromatic

When you add a secondary dominant chord to a progression, you are always adding at least one chromatic note to the progression (V/iii adds two). Since these chords have notes that fall outside the diatonic key, you get a greater variety of tones. In the example, the B would seem to smash our sacred leading tone in the key of C (B), but since it's part of a dominant chord, it sidesteps the key for a second and sets up an expected point of conclusion: IV. Once you resolve, it's business as usual and the actual V chord in the key restores the B to a B natural and the key has function again.

Which Chords?

Which chords can have secondary dominant chords? In a diatonic progression, all chords except the vii° chord can have secondary dominants. In all fairness, you can't count I either, since its dominant is not secondary but diatonic. So, here is a list of chords that can support secondary dominants:

• ii

• iii

• IV

• V

• vi

Exclude I and the vii° (diminished) chord, and you are all set. Now, you can't just throw these chords in whenever you feel like it. Well, you can, if you are writing chord progressions without melodies. But if you are harmonizing melodies, you need to be a bit more careful; certain conditions need to be met.

What Conditions?

Where exactly can you use these chords with a melody that you have already written? Well, a few things have to align for this to work. First, when you are talking about secondary dominant chords, you are actually talking about two chords: the secondary dominant and the chord it resolves to. Since both of these chords have to have connections to your melody, you need to have a situation where your melody supports both chords in succession. FIGURE 12.4 gives an example where it works really well:

Using a simple whole-note melody, you can see that the second and third chords are your points where the secondary chords come into use. The melody in bars two and three use the notes E and F. Now, you could harmonize E and F lots of different ways. When this progression was being constructed, it was obvious that it would cadence with a ii–V–I; it just sounded right after a few tries at the piano. But what about the harmony under the E? There were several choices:

• A I6 chord (C/E) could have been used to harmonize the E.

• A vi chord could have been used to harmonize the E.

• A iii chord could have been used to harmonize the E.

Theoretically, they all worked on paper. As sounds, there were some issues. The I6 chord simply sounded funny going to ii; the voice leading of the bass line going from E to D just didn't sit right. The iii chord has never sounded that compelling in any diatonic progression (it's too far from I), so that was out. The vi sounded good and would have been a solid choice; however, the V7/ii, which is an A7 chord, was ultimately chosen. The vi chord is an A minor chord; the A7 has the same bass note and two-thirds of the chord tones are the same. No wonder it worked so well!

The tricky part is finding spots to use these chords in music. Sometimes you use them and don't even realize it. Secondary dominant chords, especially V/V, are quite common in folk, country, and rock music. You may just stumble upon them in a grand, happy accident.

Secondary Diminished Chords

When the function of chords was discussed, especially when it came to the chord ladder, you learned about what chords could commonly substitute for each other. The V (dominant) chord can be substituted by the vii° chord. Both chords function as dominant chords in that they resolve back to tonic with strength and great pull. So, in the spirit of secondary dominant chords, what about secondary diminished chords? Yes, those exist, too. If the chords basically function the same way, you can use them the same way.

Secondary diminished chords have their own set of rules. Think about regular diminished chords. Typically, you see these chords as vii° chords, so you can infer some rules about their actions.

A secondary diminished chord will:

• Be either a diminished triad or a fully diminished seventh chord

• Be built a half step lower than the chord it is resolving to

• Always resolve up by a half step

As for their written symbols, instead of calling these chords V/something, call them vii°/something.

You see secondary diminished chords in classical and jazz much more than in pop music because the diminished sound is not as accepted and common as other chords.

Regardless, they are very nice chords because they have a very slippery sound to them. What does “slippery” have to do with music? It's all about the voice leading. FIGURE 12.5 provides a demonstration in the same example you had before.

Here is the same melody as in FIGURE 12.4. The note that had to be harmonized was an E. Everything else was more or less set. In FIGURE 12.4, V/ii, an A7 chord, was chosen. In FIGURE 12.5, vii°/ii, a C# diminished chord, was selected. Since the chord was only a half step below the ii chord, the secondary diminished chord slid into the ii chord. Even the bass line from the beginning of the progression—C–C–D—was a very smooth, slippery movement of bass notes and harmonies.

Both A7 and C# diminished support the E as a melody note since they both have E in their chords. In addition, if you were to step outside the key of C for a second and think about A7 as a dominant chord, you would have to imagine the key of D (the key where A7 is V). The substitute dominant chord in the key of D is C# diminished. If you compare FIGURE 12.4 and FIGURE 12.5, you'll see that all that happened was that a secondary chord was chosen for the ii chord, but each example simply substituted a dominant chord of some sort (either dominant or diminished) that resolved normally to the ii chord.

It provided a “temporary” V I (dominant tonic) relationship, on another chord besides the real tonic chord. That's why these chords work—they provide the pull, the tension and release that you need, but they do so at other points in the harmony. This may seem a bit hypothetical, but just put it to use and you will hear it for yourself.

Chromatic Harmony

The secondary chords come under the umbrella of chromatic harmony, meaning that they provide notes outside the key or they help to harmonize melodies that use notes outside the key. FIGURE 12.6 provides a simple example of a chromatic melody that is basically in C major but adds a chromatic note that is needed to harmonize

The melody is largely in C, but the F#s that have been added need to be dealt with; there are no chords that deal with F# that are diatonic to C major. But some secondary dominants or diminished chords may be. Try to harmonize the rest of the chords and exclude the F# (or at least the measure that it's in). See FIGURE 12.7.

You are left with a fairly benign I–vi–?–V7–I progression.

To deal with the chord in?, look to the chord after it, a V chord, G7 in this key.

What's the secondary dominant of that chord? V/V is D7, spelled D–F# –A–C, so it works! Plug it in (figure 12.8) and see how it sounds.

It works! Not only did you take care of the chromatic note in the melody, but you also generated a pretty interesting chord progression, one that any theory teacher would be proud to see.

Note: You could have also used vii°/V (F# diminished) as a good substitute chord for the D7 as both D7 and F# diminished. In this case, since there was a D in the melody and the diminished chord has an E, it's best to stick with D7. Functionally, it would have been okay, but to the ear it's not pretty.

Chromatic harmony is an interesting topic. Notice how composers deal with chromatic notes in their melodies and which chromatic chords they use.