IV. Diatonic Harmony, Tonicization, and Modulation

The Mediant Harmonizing Mi (Scale Degree 3) in the Bass

John Peterson

Key Takeaways

  • The iii chord (III in minor) is a weak predominant that typically moves through a strong predominant on the way to a V chord.
  • In major, iii usually harmonizes a descending ti (\hat7); similarly, in minor, III usually harmonizes a descending te (\downarrow\hat7).
  • iii/III is usually found in root position.
  • iii is not used as a substitute for I6 (see the explanation below Example 1).
  • iii is not not a very common chord.

Chapter Playlist

Overview: the iii chord

It’s most common for mi (\hat{3}) in the bass to be harmonized with a I6 chord. Occasionally, however, composers choose to use iii rather than I6 (Example 1). The iii chord is used in one relatively specific situation: after a I chord, harmonizing a descending ti/te (\hat7/\downarrow\hat7) in an upper voice. It commonly moves to to a strong predominant, though it can move directly to V in a bass arpeggiation do–mi–sol (\hat1-\hat3-\hat5) harmonized I–iii–V, and is usually in root position.

Example 1. The iii chord in Koji Kondo’s Athletic Theme from Super Mario 3 (4:19–4:24).

It’s important to emphasize that iii isn’t simply a substitute for I6 in Western classical music. For instance, in an earlier chapter on tonic prolongations, we saw that the bass line do–re–mi (\hat1-\hat2-\hat3) is commonly harmonized with \mathrm{I-V^4_3-I^6}. Composers don’t use \mathrm{I-V^4_3-iii} as an alternative. That’s because iii functions like vi, as a weak predominant that most often travels through a strong predominant to get to V. The progression \mathrm{I-V^4_3-iii} shows the opposite: V getting to iii, which isn’t stylistically normative. Finally, keep in mind that iii does not appear very often in common-practice tonality, so it should be used sparingly.

Writing with iii

Example 2 shows the voice leading for the most common use of iii: as a weak predominant that moves through a strong predominant on its way to V. In the major-mode progressions (Examples 2a and 2b), notice that the leading tone descends to la (\hat{6}) when iii moves to the predominant.

In the minor-mode progressions (Examples 2c and 2d), te (\downarrow\hat{7}) descends to le (\downarrow\hat{6}) when III moves to a predominant. Notice that III involves te (\downarrow\hat{7}), not ti (\uparrow\hat{7}). That is, III is major, not augmented, which is what would happen if we used ti (\uparrow\hat{7}).

Example 2. Writing with iii going to a strong predominant.

Example 3 shows that iii can also go directly to V. Note that this progression doesn’t work well in minor, since III contains te (\downarrow\hat{7}) but V contains ti (\uparrow\hat{7}), and the immediate juxtaposition of these two scale degrees is not stylistic for Western classical music.

Example 3. Writing with iii going to V.

Assignments
  1. Mi (\hat3) in the bass at beginnings (.pdf, .docx). Asks students to realize unfigured bass, analyze, and do a transcription with analysis.

License

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Teoría Musical Aberta (tradución en progreso) Copyright © 2022 by Mark Gotham; Kyle Gullings; Chelsey Hamm; Bryn Hughes; Brian Jarvis; Megan Lavengood; and John Peterson is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted.

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