4.3 IV as a pre-dominant

"Papa" Haydn and young Wolfgang Mozart used to love to play string quartets together. Maybe they played the one excerpted on the right.

In the above excerpt, from the second movement of Haydn's String Quartet Op.54 No.1, the composer inserted a IV chord between a first inversion tonic and a cadential 6/4. While looking vertically the cadential 6/4 is a second inversion tonic, remember that the Roman numeral V under the bracket shows that it is, in a broader context, an altered dominant. In general the IV chord in a IV - V progression functions as a pre-dominant much like ii. Therefore it is labeled "PD" as ii was on the previous page. Though the pre-dominant character of IV is not quite as strong as that of ii--since root movement is not by descending 5th--IV can substitute for ii because it closely resembles ii. The two triads have two chord tones in common. This substitution of iv for ii° is often used in minor keys (see the first phrase below) where root position ii° chords are avoided. Moreover moving from IV to V, rather than from ii to V, has the advantage of avoiding two consecutive leaps in the bass, which are uncharacteristic of vocal music.

The top staff to the left shows the standard voice leading in I IV V I progressions. As in moving from I to ii in major keys, the voice leading from IV to V is smoothest with Contrary Motion Nearest because root movement is by step and there are no common tones. The top staff also shows that iv can be used in minor keys as a pre-dominant instead of ii°5/3.

The bottom staff shows an expansion of pre-dominant harmony by using both IV and ii. Since ii leads to V more strongly than IV does, the most satisfying order is IV - ii - V, rather than ii - IV - V. The bracket under the IV and ii has "PD" beneath it to show that this is an expansion of pre-dominant harmony. Root movement is by third between IV and ii so CTS is smoothest, with two stationary common tones and one voice moving by step among the top three voices.

The excerpt below, from the second movement of Berlioz's Symphonie Fantastique (meas. 49 - 54), shows an expansion of pre-dominant harmony similar to phrase 2 above.
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