Diatonic and Chromatic Harmony
In diatonic harmony, the notes found within a passage of music use only the notes that are found in the prevailing key. In major keys this is seven notes, while in minor keys it is nine notes because of the existence of harmonic and melodic minor variants. It is possible to use chromatic nonchord tones (nonessential chromaticism) within a passage that is otherwise completely diatonic, as displayed in the next example.
When notes outside a given key are used as chord tones within a harmonic progression it is called essential chromaticism. These altered chords or chromatic chords become ever more frequent throughout the Common Practice Period.
The most used chromatic chords are secondary functions, which include secondary dominants and secondary leading tone chords. Secondary functions are used in tonicization, which involves treating a note or chord like a temporary tonic by approaching it with its dominant or leading tone chord. The main purposes of secondary functions are to intensify the harmonic drive to the next chord, to allow access to chromatic melodic and bass notes, and to provide aural relief from strict diatonic harmony.
Diatonic dominant chords are almost always either major (V) or dominant seventh (V7) chords, which means that secondary dominants must also be either major or dominant seventh chords. All triads that serve a tonic function must be major (I) or minor (i) chords, which means that only major and minor diatonic triads within a given key can be tonicized by secondary dominants. Please refer to the illustrations showing the diatonic chords in major and minor keys in the Lead-Sheet Symbols and Roman Numerals chapter in this text.
In the next example, a V/V is used in place of the ii chord in the motion to the HC.
Secondary functions, like most chromatically altered chords, are usually substituting for a more common diatonic chord. The V7/V chord, for example, is clearly substituting for the diatonic ii7 chord in the following harmonic progression, just as the V7/vi is substituting for the iii7 chord.
Spelling and Identifying Secondary Dominants
To spell secondary dominants, follow these simple steps.
- Find the note that is the root of the chord that will be tonicized.
- Go up a P5 to find the root of the secondary dominant.
- Build a major triad or dominant seventh chord on that root.
For example, write the V7/V in e minor.
Once you have learned to recognize and spell secondary dominants, it is easy to spot them within passages of music. When you find a chromatic chord within a passage of music and think that it might be a secondary dominant, use the following steps to analyze the chord.
- Check to see if the chord is a major triad or dominant seventh chord. If it is not, then the chord cannot be a secondary dominant. If it is a major triad or dominant seventh chord, go to step #2.
- Find the note that is a P5 below the root of the chord. If that note is the root of a diatonic major or minor chord within the key, then the chord is a secondary dominant.
For example, identify the following chord. Is this chord a major triad or dominant seventh chord? Yes, it is. Now go down a P5 to find the note being tonicized. Does the D serve as the root of a major or minor chord in B♭ major? Yes, it is the root of a mediant triad, which means this is a V/iii.
The most common secondary dominant regardless of mode is the V(7)/V, followed by the V7/IV (major), V(7)/iv (minor), and V(7)/ii (major only) in that order of usage. In major keys, secondary dominants of the mediant scale degree are uncommon. In minor keys, however, the V(7)/III in minor keys is occasionally encountered, and this can be analyzed as either a VII(7) or as a secondary dominant as desired.
Deceptive cadences and progressions can be highlighted by using a first inversion V(7)/vi (VI) between the V and the vi (VI), which creates a chromatic bass line in major keys.
The part-writing procedures for secondary dominants are the same as for regular V and V7 chords, so the rules regarding dominant seventh chord voice leading and the use of dominant seventh chords in circle of fifths progressions should be reviewed. Observe that sometimes secondary dominants resolve to a chord that also contains a seventh. If this happens, the leading tone in the secondary dominant can move down to become the seventh of next chord.
Below is an example of secondary dominant seventh chords being used in a circle-of-fifths progression, with the altered chords substituting for the expected diatonic chords. As with the previous example, leading tones in the secondary dominant chords will resolve down by chromatic half step to form the seventh of the chord of resolution. Please review the other conventions regarding voice-leading in dominant seventh chords that are illustrated earlier in this text.