In tonal harmony, chords are used in a hierarchy. The goal of a tonal progression and of a tonal piece of music is the tonic chord. The most common and most useful way of highlighting the tonic chord in both major and minor keys is to precede it with a V or V7 chord. The V(7) – I progression is the most important and strongest chord progression in tonal music, and it is possible to create a piece wherein most chords are V(7) and I chords.
This example is the first eight measures of a short piece by Beethoven, the Ecossaise in G. Observe how the only two chords used are the tonic (I) and dominant seventh (V7) chords. This example does contain a few nonchord tones, a concept that will be discussed later.
While most tonal works of the Common Practice Period (ca. 1600-1900) feature a sizable percentage of tonic and dominant chords, many other chords are used. Tonal harmony is based on the circle-of-fifths progression in which the roots of the chords are separated by a descending P5 or an ascending P4. The resulting harmonic sequence is very important to the history of tonal music and is seen time and time again in the music of the 17th through 19thcenturies, as well as in tonal music in the 20th and 21st centuries.
The circle-of-fifths progression can be expressed in the following charts of harmonic progression. Tonic chords (I or i) can go to any other chord. The other chords usually proceed in accordance with the circle of fifths, but there are exceptions. The mediant chord occasionally skips over the submediant chord by going directly to the subdominant chord. The dominant chord sometimes goes to the submediant triad rather than the tonic chord in the deceptive progression and deceptive cadence. Additionally, the subdominant chord often progresses to the tonic chord in the plagal progression and plagal cadence.
The subdominant IV and iv chords serve as substitutes for the supertonic chord in both major and minor keys. Similarly, the viio chord serves as a substitute for the dominant chord in both major and minor keys. Note that chord progression is essentially the same in both major and minor keys, with the addition of the major subtonic (VII) chord in minor. Also note the chord types most used in minor keys.
The following bullets points provide additional clarity:
- The I (i) chord can go to any other chord.
- V and viio chords usually progress to I, but V chords will with some regularity move to vi (VI) in the deceptive progression. Similarly, the V chord will occasionally move to IV (iv) or ii (iio) chords.
- The IV (iv) chord usually proceeds to V or viio chords but can also move to the ii chord. At times the IV (iv) will go to vi (VI) chords. The IV (iv) will also progress to the I (i) chord in the plagal progression and plagal cadence.
- The ii (iio) chord functions in the same ways as the IV (iv) chord, but the progression of the ii(o) to the viio is not as common as it is with the IV (iv) to viio. Unlike the IV (iv), the ii (iio) does NOT move to the I (i) chord.
- The vi (VI) chord advances to the IV (iv) or ii (iio) chords.
- The iii (III) chord usually progresses to the vi (VI) chord, but with some frequency will advance to the IV (iv) chord. The iii (III) almost never progresses to the ii (iio), however.
- The subtonic VII in minor keys almost invariably moves to the III chord.
Most chords used in the Bach chorales are tonic, dominant, leading tone, supertonic, and subdominant harmonies, with other chords such as the mediant and submediant chords being used less frequently. Bach’s usage of chords is a good general guideline for you to follow when you write SATB progressions modeled on Bach’s chorale harmonizations.
The way a composer uses chords and chord progressions is part of that composer’s style. You should pay attention to and compare the harmonic progressions in the music of composers who were active during the Common Practice Period. When part-writing within the tonal idiom, it is important to follow conventional progression in your writing. Most of your chord choices should follow the chart of harmonic progression from left to right. A supertonic chord, for example, normally progresses to dominant harmony. You can occasionally repeat a harmony, for example, moving from the supertonic to the subdominant, from a leading tone to a dominant chord, or from a root position tonic chord to a first inversion tonic chord. At least some movement from right to left in the table is necessary toward the beginning of a phrase to set up the progression. For example, the tonic chord may simply move back to the dominant to set up the motion back to tonic, or it can skip all the way to the mediant triad to set up a more involved progression. Last, you can skip over a class of chords in the motion toward tonic, such as when the mediant triad skips over the submediant by moving directly to the subdominant chord.