3.2 The Cadential 6/4

IN THE ABOVE EXCERPT of the American folk song, "Go Tell Aunt Rhodie", three different Roman numeral interpretations are shown below the staffs:
At 0:13 the Roman numerals I and V appear below the Arabic numerals 6/4 and 5/3 respectively. This is a straightforward interpretation since the notes above the 6 and 4 belong to the tonic triad, D, and the notes above the 5 and 3 belong to the dominant triad, A.
At 0:17 a second interpretation shows the 6/4 to be the beginning of a V chord with two suspensions (colored red). Remember that a 4th above the bass is dissonant and needs to resolve to a third. It is moreover nonharmonic with respect to V. Also with the simultaneous dissonant 4th, the note a 6th above the bass (F-sharp) is also heard as a dissonance which resolves to a 5th. This F-sharp is also non-harmonic with respect to the dominant.
So which is it? Are the notes above the 6 and 4 a second inversion tonic triad or are they a dominant chord with two suspensions?
At 0:21 a third interpretation incorporates the previous two, and this is the one which will be used in these pages. It shows the notes above the 6 and 4 to be a second inversion tonic triad above the bracket and an expanded dominant below the bracket.

Regardless of the Roman numeral interpretation the notes above the 6/4 are called a cadential 6/4. They appear at the end of a phrase, at what is called the cadence.

In summary, the cadential 6/4 is both a tonic 6/4 and an altered V chord depending on the level of analysis. When looking strictly vertically the chord is a tonic 6/4 chord. When looking more broadly the chord is an altered V, altered by two nonharmonic tones. Music theorists encourage students to look at scores broadly, but an initial analysis might quite correctly involve vertical sonorities only.

THE VIDEO ON THE RIGHT shows a cadential 6/4 expanding three fundamental harmonic progressions.
At 0:18 suspensions and an appoggiatura expand the dominant with a fourth above the bass resolving to a third.
At 0:39 other suspensions and another appoggiatura a sixth above the bass replace the fifth of V. The sixth in this context is heard as a dissonance. With respect to dominant harmony this is a nonharmonic tone. The effect of all these nonharmonic tones is to delay the appearance of scale degrees 2 and 7 in the fundamental harmonic progression's dominant chord.
The analysis at 0:57 shows an alternative, more vertical, interpretation. Since the notes above the 6 and 4 belong to a tonic chord, the Roman numeral I is placed underneath them. The Roman numeral I is followed by V with Arabic numerals removed since in root position they are understood. Nonharmonic labels are removed since the 6 and 4 are indeed chord tones according to the Roman numeral I below. Generally music theorists prefer the analysis showing a dominant chord altered by nonharmonic tones to this strictly vertical analysis.
The analysis at 1:04 is the one used in these web pages incorporating both the vertically derived I6/4 and the melodically or "linearly" derived V chord underneath the bracket. This analysis shows the original fundamental harmonic progression with which the video began.
The analysis at 1:09 reminds us that the fundamental harmonic progression is itself an expansion of the primordial tonic chord. In addition it shows the three levels of analysis discussed above.
The concept of analytical levels is a powerful one that can include the creation of the fundamental progression from an expansion of the primordial tonic, also known as Schenker's "chord of nature."
IN THE FOLLOWING EXCERPT, measures 5 - 8 from Mozart's Sonata K.331, the sixth and fourth of the cadential 6/4 are accented passing tones with respect to V, not suspensions or appoggiaturas as in the previous examples. These accented passing tones are the result of an approach from ii6 rather than from I.

Listen to more cadential 6/4s on the Harmonic Progressions Contextual Listening page.

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