The Augmented Sixth That Looks Like a Dominant Seventh
A conservatory candidate harmonizes a four-bar phrase in F minor. The penultimate chord, approached from F minor, is written with D-flat3 in the bass, F3 in the tenor, A-flat3 in the alto, and B-natural4 in the soprano. The following chord is C major in root position: C3, E3, G3, C5. The candidate labels the penultimate chord 'D-flat dominant seventh' and says it is V7 of G-flat major, then argues that resolving to C major is a chromatic surprise. The teacher points out that the phrase has no G-flat harmony and that the soprano B-natural is a leading tone to C. The exercise is in four voices, and the candidate has already checked that the bass and soprano approach the chord by step. The candidate must revise the analysis without changing any sounding pitch.
1. Give the correct Roman-numeral label and spelling of the penultimate chord in F minor, and explain why the 'D-flat dominant seventh' reading misrepresents its function.
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The chord is a German augmented sixth in F minor: D-flat–F–A-flat–B-natural, labelled Ger+6 (or flat-VI+6). The interval D-flat to B-natural is an augmented sixth, not a minor seventh. The B-natural is the raised fourth degree of F minor and functions as a leading tone to C, the dominant. Calling it D-flat dominant seventh requires spelling the top note as C-flat: D-flat–F–A-flat–C-flat. That spelling belongs to G-flat major, where it is V7 and the C-flat resolves down to B-flat. In this phrase there is no G-flat harmony, and the actual resolution is to C major. The sounding pitches are enharmonically equivalent, but the function and voice leading are not. The correct label must show the augmented sixth and the approach to V.
2. The soprano B-natural and bass D-flat both resolve to C. State the voice-leading principle, give the resulting C-major voicing, and explain what pitch is doubled.
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The governing principle is that the augmented sixth expands outward to an octave on the dominant. D-flat moves down by semitone to C; B-natural moves up by semitone to C; F moves down to E; A-flat moves down to G. The resulting chord is C–E–G–C, a complete C major triad with the root C doubled in octaves. Doubling the root is standard here because the two augmented-sixth voices converge on it; the leading-tone-like B-natural is resolved and is not doubled. The candidate should not try to avoid the doubled C by omitting the fifth or by resolving B-natural to something else; that would weaken the cadence. If an examiner asks for a four-voice check, the outer voices move in contrary motion to the octave, and the inner voices fill the third and fifth.
3. If the student respells B-natural as C-flat and resolves to G-flat major, what has changed analytically, and why is that not a simple notation preference?
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Respelling B-natural as C-flat changes the chord from an augmented sixth into a dominant seventh: D-flat–F–A-flat–C-flat, V7 of G-flat. The resolution would then be to G-flat major, with C-flat resolving down to B-flat. That is not a simple notation preference because the two spellings imply different resolutions: B-natural rises to C, while C-flat falls to B-flat. It is an enharmonic reinterpretation, and it would require a real change of key centre. In the original F-minor phrase, the G-flat reading is analytically false because the music resolves to C major and never establishes G-flat. The student may mention the enharmonic equivalence as a listening observation, but the analysis must follow the actual resolution and the augmented-sixth interval.