In previous sections, we have examined how the overtone series has aided in the development of chords, scales and the tonal system. Like these other aspects of music, harmony also functions according to some of the primary characteristics of the overtone series. However, since music is both an art and a science, historical tradition and various styles of composers have influenced what we hear as "sounding right". When discussing harmonic function in music, it may be helpful to think of it similarly to the function of grammar in a written and spoken language. There are general principles that, when followed, allow for a clear and a logical presentation of ideas. Similarly, when tonal harmonies follow certain principles, the music seems to move forward more strongly. When chords follow these principles, we say they are following a progression. When they move the opposite of a progression, it is called a regression. In some cases, chords may not clearly progress or regress -- this is labeled a chord succession. Notice that we are looking only at the roots of these chords at this time (i.e. only the roman numerals) and not necessarily the Bass note of the chords.
From the overtone series, we learned that the tonic is the most stable pitch class within a key, being lowest on the series. The dominant (scale degree 5) is next in the series, which acoustically has a tendancy to want to resolve to tonic. The V chord also contains scale degree 7, which also has a tendancy to resolve to tonic. As a result, the dominant triad has a tendency to most strongly want to resolve to the tonic triad. This forms a V - I progression, and is the strongest type of progression in tonal music. It is even stronger when a seventh is added to the dominant triad, since scale degree 4 (seventh of the V chord) has a tendancy to resolve to scale degree 3 (third of the I chord). Listen to the following, and notice how at the end, when the final I chord is delayed, there is a very strong desire to have the V chord "resolve" (progress) to the I chord.
Notice that the roots of the V - I progression move down by the interval a fifth or when inverted, up by a fourth. Although this type of progression is most strongly felt in the V - I progression, other chords that progress in a down-by-fifth/up-by-fourth progression also strongly move forward.
Composers have recognized this principle, and have often used down-by-fifth/up-by-fourth progressions in their music. When a composer uses a long string of this type of progression, we call it a circle of fifths progression, since it moves through all of the chords in the key and returns back to the starting chord.
From this we can see how most chords have a tendency to wish to resolve using this type of progression. All of the following are down-by-fifth/up-by-fourth progressions:
* - because the diminished vii chord is so unstable, and has a strong desire to resolve to the tonic (see below), it is rarely used in an down-by-fifth/up-by-fourth progression except as a part of a circle of fifths progression.
As noted in the section on Scales and tendancy tones, the seventh scale degree has a strong tendency to resolve to the tonic. Root movements that are up by the interval of a second are also very strong harmonically. Up-by-second root movement progressions are frequently used in tonal music, often in combination with down-by-fifth/up-by-fourth progressions:
Listen to the following example, popularly used in much of the rock and roll of the 50's:
Notice that the root movement of the chords is down by the interval of a third. In progressions of this type, there are always two common tones between adjacent triads. The remaining tone resolves up by second, providing the forward movement. Although, because of the common tones, this progression is weaker than the above two types, because of the smooth connections between chords, it is still commonly used. However, it is rarely used at the end of a musical passage, since a stronger resolution is desired at those points.
From this we can see how most chords have a tendency to wish to resolve using this type of progression. All of the following are down-by-third progressions:
* - because the V chord has such a strong desire to resolve to the tonic, it is rarely used in an down-by-third progression.
** - because the diminished vii chord is so unstable, and has a strong decide to resolve to the tonic, it is rarely used in an down-by-third progression.
As noted, only the V and vii° triad and seventh chords have exceptions to the basic harmonic progressions. From this, a simple saying to remember harmonic progressions can be used:
As a confirmation of the exceptions, listen to them and notice how they don't seem to sound quite "right". This is because both V and vii° have a very strong tendency to resolve to a I/i chord. A iii/III chord is very close to a I/i chord, with only one note difference. Since our ears are more used to hearing a resolution to a tonic chord, this "different" note is more often heard as a mistake rather than an actual, intended progression.
Does this mean that all music that follows progressions is good and that which doesn't is bad? No, composers have always used harmonic regressions and successions in their music, just as much of the great literature of the world has instances of non-standard grammar. However, if we are to better understand music, it is important to recognize when composers chose to use progressions and when not to use them. Skillful use of progressions in passages where the composer wishes the music to move ahead more strongly, and successions/less strong progressions when they want the music to relax a bit is what creates an interesting flow to the music. An occasional regression may be used to provide a surprising moment in a composition. However, most of the music of the common practice period follows harmonic progressions, so it is very important to memorize and be able to recognize these functions within their musical context. This will not only allow you to better enjoy listening to music, but will also aid in deciding how to interpret the performance of common-practice music.
When writing your own harmonies, it is important to keep in mind the following guidelines: