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Part-writing Chords: Mediant and Submediant I

The mediant and sub-mediant chords—triads built upon the third and sixth scale degrees, respectively—are less frequently used than the triads previously considered in this series of Hubs. (This is especially true of the mediant.) It’s partly for this reason that these two chords can be used to broaden and freshen harmonic color.

Before looking at some normal uses of these two triads, though, the reader may wish to check whether it would be helpful to work through some of the previous Hubs in this series—the knowledge contained in them is assumed in the rest of this Hub. Below are lists of the topics that are covered in each of the preceding Hubs.

Part-writing Hub #1

  • Lead sheet
  • “Spacing” of voices
  • Parallel and contrary motion of voices
  • Concept of “voice leading”
  • “Root position,” “voicing,” and “line”
  • Polarized roles of tonic and dominant chords in Classical harmony
  • Resolution of “leading tone”
  • “Open” versus “close” chord spacing
  • Chordal “doubling”
  • “Common tone”

Part-writing Hub #2

  • Vocal ranges
  • Rule for determining sharp keys from key signature
  • Rule for determining flat keys from key signature
  • Chords with missing thirds
  • Part-writing Chords: Subdominant I
    Third in a series, this Hub examines the use of the subdominant chord--the "IV chord"--in traditional ("common-practice") harmony, with practice exercises.

Part-writing Hub #3

  • Root motion by fifth
  • Root motion by second
  • Parallel motion [perfect or imperfect intervals]
  • Similar motion; similar fifths and octaves
  • Incomplete triads [omitted fifths]
  • Tripled root voicing

Part-writing Hub #4

  • Primary and secondary triads
  • “Doc Snow rule of doubling”—better known in association with Walter Piston!
  • “Hybrid spacing”
  • IV normally precedes ii in Classical style
  • Chord substitution
  • Deceptive cadence
  • Voice overlap

If any of this seems unfamiliar or confusing, it would probably be best to spend some time working through (or at least reviewing) the relevant material.

As always, I strongly suggest answering the questions physically, on actual music manuscript paper, as you proceed through this Hub. As usual, I’m providing a link to free manuscript paper that you can print out.

In the previous Hub we considered the concept of chord substitution, noting that since third-related diatonic triads—as, for example, ii and IV—share two of three chord members, they will thereby exhibit some sonic similarity. Supertonic and subdominant—ii and IV—are especially vivid examples of this tendency, since in normal usage both chord tend to lead to a dominant triad—the “V” chord. That is what music theorists mean when they say that both ii and IV “function” as preparations for the dominant.

(In fact, this notion of chordal “function” is widespread and influential; theorists recognize chords of all sorts as possessing “tonic,” “dominant” and “dominant preparation” “functions.” But that is a discussion for a later Hub.)

First, let’s look at the mediant and submediant in the context of the major scale:

Example 1

Example 1

As shown, the mediant is the iii chord. Its name seems to recognize the fact that its root lies midway between tonic and dominant in the scale:

Ex. 2

Ex. 2

Correspondingly, the submediant, vi, has a root lying midway between that of the tonic and the subdominant.

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Ex. 3

Ex. 3

The mediant and submediant can also be placed in a more specifically harmonic context, though. We noted in the last Hub how tonally strong, and how common, the progressions ii-V-I can be. This is so because of the powerfully stabilizing root motion by fifth it exemplifies:

Ex. 4

Ex. 4

This motion can be further extended ‘backwards’ to incorporate the submediant and mediant chord, too:

Ex. 5

Ex. 5

Notice the striking sound of the mediant—but also the purposeful flow of the harmony, dominated as it is by the tonally strong root motion by descending fifth. These harmonies seem to drive toward the tonic with great energy and purpose, moving systematically from the most 'distant' diatonic chord, the mediant, to the tonic.

Notice, too, that the second and third chords—iii and vi—form a unit that is replicated down one scale step by the fourth and fifth chords—ii and V. This type of transposed repetition is termed a ‘sequence’ and it’s a useful musical technique.

Let’s try writing variations of that progression. Identify the key and scale degrees in the soprano below:

Question 1

Question 1

It’s in Ab, and the scale degrees in the soprano are 5-5-6-4-5-3.

Using the example above as a model, add a bass line.

Now add alto and tenor voices in turn.

Here’s another twist on the same chord progression. Name the key and scale degrees in the soprano below. Also, which of the lines in the previous question does this soprano resemble?

Question 2

Question 2

The key is D major, the scale degrees are 1-7-1-6-7-1, and the line is very close to the tenor line in the preceding question; only the last note is changed. Why does that last note need to change?

While you ponder that, add a bass line.

You may have thought that the line needs to change because the C# at the end of the first full measure is the leading tone, and when ‘exposed’ in the soprano or bass, instead of ‘hidden’ in the alto or tenor, it needs to resolve to the tonic. If so—congratulations! That’s exactly right.

Now add alto and tenor.

Another harmonic context for vi and iii occurs when, rather than appearing ‘as themselves’ in a ‘falling fifths’ progression like those we have just been examining, the mediant or submediant appears as a substitute for some other chord.

Which substitutions are possible? That is, which triads are a third away from (and therefore share two tones with) the mediant and submediant? The answers will be obvious to some readers, and perhaps puzzling for others. If you are not one of the first group, don’t give up right away. Write out on paper the lower two notes and the upper two notes of the vi chord:

Example 6

Example 6

Now do the same for the iii chord. For each pair of notes, there will be one tone which will form a ‘new’ triad. Work through the four possibilities. You should end up with something very similar to this:

So, vi can potentially substitute for I—as mentioned in the last Hub of this series, this commonly happens in the context of the “Deceptive Cadence”—or for IV. It isn’t hard to find examples of vi leading to V, which could be thought of as vi substituting for IV, although it isn’t usually viewed in that way.

The mediant triad, similarly, could substitute for either I or V. If you think about it, that is a remarkable thing, since, in the context of Classical practice, tonic and dominant functions form the opposite poles of tonal harmony. Possibly this very ambiguity helps explain why one sees relatively few examples of the iii triad. Yet there are usages which suggest precisely these mediant substitutions, as we’ll see.

Beginning with the submediant, here are two versions of the progression I-vi-V-I. As mentioned a moment ago, one way to think of this would be that the vi chord substitutes for the IV chord we would expect to lead to V. Like the IV chord, vi has a potential pitfall when leading to V: since the root motion is by second, objectionable parallel fifths or octaves could easily arise. This danger must be avoided by making sure that the upper voices—or at least those involving root and fifth of the V chord—must move in contrary motion to the bass. Here are two examples: