MUS 111 Study Guide F (Chapter 6)

The Subdomiant Triad

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  1. Spelling the subdominant triad:  root is built on the fourth scale step of the key. In a major key, the triad is major. In minor it is "usually" minor, but not always. When melodic considerations require the use of the raised sixth scale degree (melodic minor), the chord becomes major.
  1. Plagal cadences:  Like the dominant triad, the subdominant triad can also be used during the course of a phrase and also as part of a cadential progression.  A cadence from the subdominant chord to the tonic is known as a plagal cadence, and may be found in the same forms as authentic cadences (perfect or imperfect).
  1. Perfect Plagal:  The progression IV-I or iv-i in which the subdominant has its root in the bass and the final tonic triad has its root in both the bass and soprano.
  1. Imperfect Plagal: The progression IV-I or iv-i in which the final tonic triad is found with its third or fifth in the soprano. (The commonly used soprano lines are scale degrees 6-5, 4-3 and 1 up to 3.)
  1. Half Cadence:  A rare cadence such as I-IV or i-iv. The only justification for labeling it as a "half" cadence is that the intervals of the fifth and fourth are inversions of each other.
  1. An easy way to remember the sound of the plagal cadence is that it is used as the "Amen" cadence at the end of hymns.
  1. IV or iv in other progressions:  The subdominant triad may progress freely to or from the tonic or dominant.
  1. When the authentic cadence is preceded by the subdominant in the progression IV-V-I, or iv-V-i, the term full cadence is sometimes applied.
  1. The tonic, dominant and subdominant chords are widely used in the harmonization of folk and popular tunes. They are sometimes referred to as primary chords.
  1. Writing the progression IV-I or iv-i:  Since the roots of the IV and I triads are a fifth (or fourth, in inversion) apart, the part-writing procedures are the same as for V-I re common tones, third-to-third skip, etc.
  1. Writing the progression IV-V or iv-V:  When the roots of two triads are a second apart, as in IV-V, no common tone is available. The common practice is for each of the three upper voices to move to the nearest triad tone in contrary motion to the bass.  In that the bass ascends in IV-V, the soprano should normally descend to avoid parallel motion.
  1. Parallel Fifths and Octaves & the melodic augmented second:  these are three part-writing problems to avoid.  Parallel fifths and octaves can occur between any two voices and are sometimes easy to overlook ... be forewarned.  (There is nothing innately wrong with these parallelisms, however, they were not found in works of the common practice period and are to be avoided.  Later composers used these parallelisms effectively.)  Incidentally, a repetition of two consecutive fifths or octaves on the same pitches is not considered parallel, but stationary, so no prob there.  Attempting to hide parallel octaves or fifths by dropping one voice an octave does not solve the problem; the intervallic motion is still considered parallel.  The permissible exception to this guideline would be in a final cadence where, for example, the soprano and bass are on the root of the V chord and both move in contrary motion to the root of the I chord.

The melodic augmented second occurs in a minor key with the scale motion b6-#7, which, again, is uncharacteristic of the common practice period.

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