Harmonic Functions

1. The “Roles” Chords Play

In the previous article you learned that six prime chords are divided into two parties, constructing 3vs3 symmetric correspondence.

IIVV are all major chords, and VI_mII_mIII_m are all minor chords. But when they form a chord progression, each chord gives a distinct impression to you, by the power of contexts. Typically, when a song progresses to I chord, there’s a sense of rest, landing, ending, home or closure, just like what you feel when melodies reach the tonal center of music.

IVIVI

Even listeners without any musical training recognize these relative roles of chords (unconsciously) and enjoy the “story” of music. Isn’t it an intriguing phenomenon? It is thought that this musical ability is naturally acquired in early childhood.

In music theory a role of a chord within contexts is called Function and theories based on the idea of function is called Functional Harmony.

Function

Significance of a chord within the key, the role that a chord plays in a musical context¹.

THIS SECTION IS VERY IMPORTANT. You’ll see how to create a “story” of music by chord progressions.

Variations

But in fact, “functional harmony” has a plenty of variations. Different branches have different functional harmony, or even within one branch, authors have their own views on chord functions. The original version—which was born in Germany in late 19^th century—defined numerous functions, chiefly divided into 3 main categories.

But as you can see, the symbolization system was so complex that it failed to get popularized. But later theorists were inspired by this idea, borrowing the term “function” and made up their own “functional harmony”, which is why there are so many variations of it². In this article I first introduce a classical one, which I think is fit for popular music, then in the end I’m gonna talk about the variations.

2. TDS Functions

Starting with the major party, I is the captain of a key. Reaching the chord will make a sense of the end.

In Classical music, a major key song must start with I, end with I. This is the role, the “function” of I chord.

Difference between IV and V

Then what about its “lowermate” and “uppermate”, IV and V? They both have a momentum to develop a song but their characters are distinct from each other.

IIVIIV

IVIV

Though it’s difficult to verbalize these qualities, IV creates a relatively soft, calm or gentle mood while V has more active and driving sense like reaching the peak.

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So where they shine is totally different. For example, V will do a great job when inserted right before the chorus part. IV is a perfect one when you start a part with softly floated feel, and so on.

Function Names

Though I spent a lot of words to express the “feel” of each chord, it’s virtually beyond description. So we give special names to each function:

The simple letters TDS represents the “role” of each chord³.

3. Function in Minor Key

The rest of prime chords are all minor chords, who constitute the minor key environment.

They forms the same relationship—The captain, the lowermate, the uppermate. So the roles they play are analogous to the major counterparts—VI_m works as home, II_m and III_m expand the story, the former is a bit softer while the latter is in a sense stronger.

VI_mII_mVI_mII_m

VI_mIII_mVI_mIII_m

It will be rather difficult to tell the difference between II_m and III_m, but anyway, they have distinct characters. So music theory postulates that the three have the same kind of functions as those of major chords, though it may not be completely equal.

4. Context-Dependency

In other words, TDS is the formal names for “captain/uppermate/lowermate”. With functional harmony theory, the scheme of six prime chords is abstracted even one level higher.

Now prime chords are organized in a simple matrix😎

But in actual songs, major chords and minor chords get together to create mixed key environment. In that mixture, the role of a chord may get ambiguous. The typical one is III_m.

The chord, placed at a very peculiar position in a key, occasionally works more like the “variation of I” than the “uppermate of VI_m“, depending on situations.

IVIII_mII_mVI_m

This is one of the situations. If we see this III_m as D function, it suggests the similarity with V, which consequently suggests the availability of substitution for it. But if you do substitute……

IVVII_mVI_m

The story of music seems to be changed radically. This shows that in this situation III_m is not much like D function, but more like the function similar to I.

IVIII_mVI_m

When replaced with I, though it sounds much more stable, the outline of musical story is preserved better than V. In some functional harmony theories, such III_m is defined as T function. Please note that it is not the sonority of a chord itself, but the contexts (including chords before/after it, phrases put on it, rhythms etc) that defines the function.

It is interesting that the same sounding chord acts different characters. Discussing such context-dependency of a chord is one of the main purposes of why the original functional harmony theory was adovocated.

• The Context-Dependency of a Chord Function
  An apparently identical chord can have different “roles” depending on contexts. For example, IIIm may act either as D or T. It can be judged through an analysis of its musical contexts and contents⁴.

So actually, to analyze chord functions, it is necessary to observe the flow of the entire chord progression, but in theory books, there inevitably are times when only one chord is placed alone for some explanation. In such cases, III_m is primarily regarded as D for convenience in this text, but please keep in mind that contextual information is actually needed.

Summing up, IVI_m are T acting as captains. IVII_m are S, the sense of leaving home softly. And VIII_m are D, creating the peak of development, but the two are not “intimate” and less interchangeable. III_m is like a wanderer in a key getting closer to I occasionally…… This is the total overview of the six prime chords.