2. Pre-dominant and Plagal Triads and Listening Strategies for Identifying Pre-dominant Triads: Voice-Leading and Chord Quality Methods

Pre-dominant and Plagal IV Chords

I. Pre-dominant Function

Harmonic progressions often follow the phrase model:   T Pd D T

The symbols T, Pd, and D stand for particular harmonic functions: tonic, pre-dominant, and dominant.  A chord’s function is the role it plays within a harmonic progression.

Pre-dominant (Pd) chord —  a non-tonic chord that leads into a dominant-function chord.

The subdominant IV and iv chords are the prototypical pre-dominant chords.  They often lead to V.  Later we will find that ii6 and iio6 chords often serve the same function.

II. Plagal Function

Not all subdominants are created equal.  Not all subdominants are pre-dominants!  A IV chord (or iv chord in minor) can lead to a I chord (IV-I), as well as to a V chord.

Plagal (Pg) chord —   a chord that goes to tonic although it does not have a leading tone 7; instead, it typically has a 6 that moves to 5.

Plagal chords generally embellish tonic by the motion in their upper parts:

 

Plagal patterns

In traditional twelve-bar blues, there are two plagal IV chords.  Provide functions for the 12-bar blues progression below:

 

12-bar blues

 

Distinguishing between Pre-Dominant Triads with Scale Degree 4 in the Bass

(compatible with Karpinski, Chapters 38 and 39, but focused on one particular task)

Once you can track the motion of bass lines consisting of scale degrees 1, 4, and 5, it is natural to begin to distinguish between root-position and first-inversion triads that can be built on scale degree 4.  Pre-dominant chords are often built on scale degree 4 in the bass.

What two Pd triads are possible above this scale degree?  Fill the blanks in the charts:

Two Methods: Voice-Leading and Chord Quality

There are two main ways to distinguish between IV and ii6: (1) The voice-leading method and (2) the chord quality.

First, to use the voice-leading method, hang onto ^1 as the tonic chord changes to the pre-dominant with your voice (and later, just with your ear). Find out whether this scale degree is a comfortable fit within the pre-dominant or if it is dissonant with it.  If scale degree ^1 fits, the chord is IV.  If scale degree ^1 is somewhat dissonant, the chord is ii6.

Also note that scale degree 2 will fit comfortably within a ii6, but will be somewhat dissonant with the IV chord.  The voice-leading method works the same way in minor keys as it does in major keys.

Second, the chord quality method works by learning to hear the differences between major, minor, and diminished triads.  In a major key, IV is major and ii6 is minor.  In a minor key, iv is minor and iio6 is diminished.

 

A Side Note on the Usefulness of Attending to Harmonic Function:

We know that scale degree 4 can also as part of a dominant-function chord.  In that case, it will sound dissonant and will resolve down to ^3.  (Why is that?  What is ^4 in the context of a V42 chord?)  In a pre-dominant chord, however, the bass note ^4 is consonant and will normally go in the opposite direction, rising to ^5.  By knowing the function of the chord, we limit the range of possible chords greatly.

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