IV. Diatonic Harmony, Tonicization, and Modulation

Mi (scale degree 3) in the bass at beginnings

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 [latex](\hat7)[/latex]; similarly, in minor, and III usually harmonizes a descending te [latex](\downarrow\hat7)[/latex].
  • 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 ([latex]\hat{3}[/latex]) 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 relatively specific situations:

  • After a I chord,
  • Harmonizing a descending leading tone (or subtonic in minor) in an upper voice,
  • Commonly moves to a strong predominant (though it can move directly to V in a bass arpeggiation domisol [latex](\hat1-\hat3-\hat5)[/latex] harmonized I–iii–V), and
  • 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 we saw that the bassline doremi [latex](\hat1-\hat2-\hat3)[/latex] is commonly harmonized with [latex]\mathrm{I-V^4_3-I^6}[/latex]. Composers don’t use [latex]\mathrm{I-V^4_3-iii}[/latex] 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 [latex]\mathrm{I-V^4_3-iii}[/latex] shows the opposite: V getting to iii, which isn’t stylistically normative. Finally, we should emphasize once more that iii is not a very common harmony, and we recommend using it sparingly in Western classical music.

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 when iii moves to the predominant.

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

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 [latex](\downarrow\hat{7})[/latex] but V contains ti [latex](\uparrow\hat{7})[/latex], and the immediate juxtaposition of these two scale degrees is not stylistic for Western Classical music.

Example 3. Writing with iii going to V.

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


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