Download Tonal Harmony Chapter 22 Augmented Sixth Chord

Chapter Twenty-Two
Augmented Sixth Chord
Augmented Sixth Chords
 One way to emphasize a tone is to approach it by a half step, either from above or from below
 It is a strong approach to the dominant by half steps above or below
Example: Key of g minor
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C#-D
E--D
+6 V
This method of approaching the dominant distinguishes a whole category of pre-dominant chords
called augmented sixth chords
The characteristic elements of most augmented sixth chords:
o The chord being approached is the V chord
o The minor-mode 6th (chromatically lowered if in a major key) appears in the bass
o The #4th is in an upper part
The interval of an +6 formed by these pitches is enharmonically equivalent to a m7, but the
difference between the effect of the +6 and that of the m7 is easily detected by the ear
m7 tend to resolve downward while +6 resolves upward
The analytical symbol of an augmented 6 is +6 and not a roman +VI
The interval of the +6 usually resolves outward by half step, following the tendencies of the tones
to lead to a dominant
Less commonly, the top pitch of the +6 may descend chromatically to produce the 7th of a V7.
This occurs only when: i) +6 chords have three or more pitch classes; ii) the top pitch of the +6
(#4) interval in an inner part
+6 chord is among the strongest of all predominant chords, and it generally moves directly to V
(or i 64 -V)
Frequently used just after a modulation to make it clear to the listener that a modulation has, in
fact, occurred
Like N6, the +6 originated in the minor mode, but it was soon found to be equally useful in major
keys
When used in major keys, it is often preceded by mode mixture
The Italian Augmented Sixth Chord (#4 + b6 + 2xtonic)
 In most cases, +6 chords contain more than two pitch classes
 The third pitch class is usually the tonic pitch, which lies a M3 above the bass pitch (b6th)
 This combination of notes is referred to as an Italian augmented sixth chord (It+6)
It+6
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The It+6, like any other +6 chord, resolves to V or I 64 – V
The tonic is doubled in a four-part texture
The French Augmented Sixth Chord (2 + #4 +b6 + tonic)
 It+6 chords with one pitch added, the 2nd, the sonority is referred to as a French augmented sixth
chord (Fr+6)
 Be sure to label a French +6 chord as Fr+6, and not F6, which is a lead-sheet symbol
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Fr+6 works best in 4-part or free texture
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Fr+6 occurs occasionally in popular music and jazz. The symbol used calls for a Mm7 chord with
a lowered 5th. In the key of d minor, Fr+6 would be symbolized as Bb7(b5)
The German Augmented Sixth Chord (It+6 plus minor mode 3)
 May be thought of as an It+6 with the addition of a minor mode 3 (chromatically lowered if in a
major key)
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As with any +6 chord, the usual resolutions of the Ger+6 are to V and to i 64 – V
When the Ger+6 moves directly to V, parallel 5ths are apt to result, because the ear is distracted
by the resolution of the interval of the +6, the parallels are not so objectionable, and they may
occasionally be encountered
Composers usually manage either to hide the parallels through anticipations or suspensions or to
avoid them through the use of leaps or arpeggiations
A simpler resolution to the problem of the parallels is to delay the V through the use of a
cadential six-four
The last Ger+6 in example 22-13 spelled differently from the others, although it sounds the same
(A#=Bb). This is a common enharmonic spelling of the Ger+6, used in the major mode only, when
the Ger+6 is going to I64
The reason for the use of enharmonic spelling is more for the eye than for the ear: A# to B♮ looks
more reasonable than Bb to B♮ because we usually expect raised notes to ascend and lowered
ones to descend
Ger+6 chords are encountered frequently in lead-sheet symbols, where they are indicated as a
Mm7 chord on the minor sixth scale degree, as in C: Ab7-G7, which represents C: Ger+6 – V7
Jazz theory explains the Ab7 as a triton substitution; that is, the Ab7 is a substitute for a D7 (V7/V)
chord. Their roots are a tritone apart, and the two chords share a tritone: C-Gb in the Ab7 and CF# in the D7
Other Bass Positions
 Not yet a topic of discussion because the augumented chord is a linear sonority that has no root
 A Fr+6 can be arranged to resemble an altered V7/V, and the It+6 and Gr+6 sonorities can be likened
to altered iv7 chords
 minor 6th is usually constitute the bass of an +6 chord, other bass position do occur, especially in
music of Romantic period
 The only other bass position that occurs with any frequency is that with the tonic pitch in the bass
 Because +6 chords have no root and therefore technically cannot be inverted
Resolution to Other Scale Degrees
 The augmented interval (+6) of the chord usually embellishes 5th degree, we could have used
symbols like Ger+6/5th, but it is understood that “/5th” is implied when we write “Ger+6”
 In Romantic period, the +6 is sometimes applied to scale degrees other than the 5th, and those
cases, we make this clear as shown below:
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To spell or recognize the various +6 types, you will have to familiar with the intervallic structure
of the three kinds of augmented sixth chord
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Often when an augmented sixth chord resolves to something other than V, the chord that it
resolves to is a secondary dominant. In that case, it is probably better to show the analysis in
relationship to the chord being tonicized