When part-writing augmented sixth chords, like the assignment on page 276, having a set of things to focus on, and an order to approach the problem, can be a big help. Here’s my approach for part-writing augmented sixth chords:

• If you’ve been given Roman numerals with inversion symbols, then the bass line is given. Write the complete bass line first.
  • Remember that in minor keys, there is no chromatic alteration needed for the b^6 root of an augmented sixth chord. In major keys, you will have to lower it a chromatic half step.
• Next, deal with the interval of the augmented sixth. You should always deal with dissonant intervals first. They usually must be approached with more care, and resolved in special ways.
  • Spell the  augmented sixth interval in your head, and then find the voice that gives you the smoothest voice-leading to it.
  • Remember that you should avoid augmented melodic intervals.
• Finally, fill in the rest of the chord tones of the aug. sixth chord according to its type. (Italian requires a doubled third above the root, etc.)
• Moving away from the aug. sixth chord,
  • resolve the augmented sixth interval first. (This way you don’t try to move some other voice to the same note, and then not resolve the interval properly.)
  • Move the remaining voices smoothly to the remaining chord tones.
  • With the Italian +6, the voices doubling the tonic (chordal third) will move in contrary motion to each other.
  • The German +6 almost always goes to a cadential 6/4 to avoid parallel fifths. The chordal third is a common tone, and the fifth is either common (in minor), or moves up a chromatic half step (b^3 – ^3).
  • The French +6 provides a common tone to the fifth of a V (the fourth above the bass holds to become the fifth above the bass), and the chordal third moves down the leading tone.

The overall approach is to focus first on the given (the bass line), then the special dissonance (the augmented sixth interval), and then the remaining chord tones.

Some added things to consider with Augmented Sixth chords:

Never double either tone of the +6 interval. In four-voice texture, only the Italian +6 would involve doubling, and you would double the third of the chord (tonic), the only other chord tone not part of the +6 interval.

You should learn the figured bass along with the national names. I can’t notate this clearly in the blog except through a graphic:

Augmented sixth chords will sometimes resolve to scale degrees other than ^5. The most common is tonic, but others are possible. In this way, +6 chords act as secondary dominants, and should be labeled as secondary chords. (It+6/I, for example)

The +6 interval could be inverted to a °3. This creates a type of substitution for V/V in the ii6 – V/V – V progression and other similar ones. The bass line steps up ^4, #^4, ^5. The resulting chromaticism in the upper voices is very striking, and much different from the secondary dominant of V.

The +6 chord can resolve deceptively. I won’t go into this too much at this point.

Augmented Sixth chords (+6) use the interval of an augmented sixth to resolve outwards to (typically) ^5 and dominant harmonies (cadential 6-4 included). Remember that augmented intervals will generally resolve outward.

The chord is built on the b^6 scale degree, with the inclusion of #^4 to form the augmented sixth interval. These two scale degrees can be thought of as leading tones from both above and below ^5.

The augmented sixth chord typically appears in one of three forms: Italian, German, and French.

• The Italian +6 is comprised of b^6, ^1, and #^4. It is the simplest (fewest chord tones) of the +6 varieties.
• The German +6 adds b^3 to the Italian version, resulting in b^6, ^1, b^3, #^4 (a major triad with an augmented sixth). Note that the German and Italian +6 chords are enharmonically equivalent to V7 chords. The spelling is important, as chordal sevenths resolve down by step, and augmented sixths resolve outward to the octave.
• The French +6 adds ^2 to the Italian +6, resulting in b^6, ^1, ^2, #^4.

Note that all varieties of the +6 chord include b^6 as the root, tonic, and #^4 (major third and augmented sixth intervals from the root).

Anecdotal evidence ascribes the Italian designation to the more usual simpler nature of Italian harmony (than German). It might also be found that Beethoven (a German) used the German variety more frequently. No one is quite sure. The French designation, however, is quite appropriate. The French +6 chord belongs to a whole-tone scale, the use of which began to develop with French music around the turn of the 19th to 20th century.

Bring your Anthology on Wednesday. 

Chromatic Harmony and Enharmonic Spellings

With chromaticism increasing, be prepared for some harmonies to be enharmonically spelled. Enharmonic spellings can be used to make the music easier for the performer to read. For example, in Ab Major the bII chord is Bbb – Db – Fb. Yuck! It can be enharmonically spelled A(natural) – C# – E(natural). Good. The same goes for bVI, or V7/bII. In Ab major, bVI is spelled Fb – Ab – Cb, but can be enharmonically spelled as an E major triad.

Enharmonically spelling a chord does not change its harmonic function, and you need to learn to recognize the enharmonic spelling and use the appropriate Roman numeral label. For example, finding an A major triad in the key of Ab major, that leads to an Eb-flat dominant 7 has to be recognized as an enharmonic spelling of bII, and labeled as such. You would never label it #I.

It is also possible that you might encounter a passage with an extended section of bVI and bII spelled enharmonically, where the key signature changes to reduce the number of accidentals needed. This type of key signature change would not indicate a new key area/modulation.

Later on we will study how composers can use enharmonic spellings to actually change the function of harmonies and move to distantly-related keys. (It’s like theory magic.)

Review

• bII usually appears in first inversion, with the third of the chord doubled.
• The b^2 scale degree must move down to the leading tone (possibly with motion through ^1).
• If bII is in root position, double the root (giving you two instances of b^2). b^2 in the bass will usually move to ^5 (as part of the movement to the dominant). b^2 in any voice besides the bass will resolve according to expectation (see above).
• In major, bII will also need b^6.
• bVI (or VI in minor) is the dominant of bII, however, you only label it as the dominant of bII if it is a Mm7 (dominant7) chord, i.e., V7/bII. Never label V/bII. Instead use bVI.