6.3 Imperfect Authentic Cadences

Beethoven's "Für Elise" begins with a parallel period, similar to those on the previous page, except that the antecedent ends with V - I and has scale degree 3 as the last note. This melody note makes this cadence weaker than the consequent's cadence since the consequent ends more conclusively on scale degree 1. The antecedent's cadence is an example of one kind of imperfect authentic cadence (IAC):
  • It is "authentic" because of the dominant to tonic harmony, and
  • it is "imperfect" because, unlike a perfect authentic cadence, the top voice ends on scale degree 3 instead of 1.
This and other kinds of imperfect authentic cadences are described below.

In general an imperfect authentic cadence (IAC) is a cadence which ends EITHER with
  • V(7) - I, both in root position, and scale degree 3 or 5 as the last note of the melody OR
  • V(7) - I, either or both chords inverted OR
  • a combination of the previous two OR
  • vii°6 - I with scale degree 1, 3 or 5 as the last note of the melody. vii°6 is considered dominant harmony because it contains the leading tone and tends to resolve to I.

Composers almost always write imperfect authentic cadences which have root position chords and a melody ending on scale degree 3 or 5. That is, it is rare that a cadence is imperfect authentic by virtue of an inverted dominant or tonic harmony or by vii°6 substituting for V.

Do not write a double slash after an antecedent phrase with an imperfect authentic cadence. With this cadence the dominant does not interrupt the large scale I - V - I harmony of the fundamental harmonic progression. Instead, the I triad at the end of the antecedent continues a long deep level tonic harmony which lasts, in the case of the "Für Elise" illustration, all the way to the next-to-the-last measure. See also the deepest level bracket in the example below.

In summary in the first two phrases of "Für Elise" the pause on an inconclusive tonic expands a single phrase of music into two phrases.

The video to the left shows a parallel period with imperfect authentic and perfect authentic cadences. Notice the absence of double slashes at the end of phrase 1 and the long deep level tonic which spans most of the period.

The old time fiddle tune "Buffalo Gals" (below sung and played on a banjo by Pete Seeger) contains a parallel period with Imperfect Authentic and Perfect Authentic cadences. The excerpt which is shown in music notation begins at 0:46.

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