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 [latex](\hat7)[/latex]; similarly, in minor, 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 one relatively specific situation: after a I chord, harmonizing a descending ti/te [latex](\hat7/\downarrow\hat7)[/latex] 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 [latex](\hat1-\hat3-\hat5)[/latex] 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 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, 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 [latex](\hat{6})[/latex] 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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