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IV. Diatonic Harmony, Tonicization, and Modulation
The Mediant Harmonizing Mi (Scale Degree 3) in the Bass

### Core Idea

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).

### Explanation

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

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.

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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.

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Example 3. Writing with iii going to V.

Assignments

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

### Key Quote

The iii chord (III in minor) is a weak predominant that typically moves through a strong predominant on the way to a V chord.

### Application Scenarios

iii is not used as a substitute for I6 (see the explanation below Example 1).

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](https://viva.pressbooks.pub/openmusictheory/chapter/strong-predominants/), 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](https://open.spotify.com/track/7xGGMrIo22rfpoaFmV1dVd?si=2a9edd4390574f8b)).

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 ([[B]]Examples 2a [[/B]]and[[B]] 2b[[/B]]), notice that the leading tone descends to la (\hat{6}) when iii moves to the predominant.

### Key Terminology

voice leading root position scale degree leading tone bass line Western scale tonic chord root note

### Related Links

Chapter Playlist strong predominant 4:19–4:24 in an earlier chapter on tonic prolongations pdf docx
Source: https://viva.pressbooks.pub/openmusictheory/chapter/the-mediant/
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