Popular and Jazz music annotates chords in the same way as we have done in the chapters related to chords (for instance, chapter Often used chords). Such notations are convenient for the task of playing music. For instance, the C major chord will always be shown in the same way (with the symbol C), no matter in which key it occurs, like the C major key or the F major key. Thus, once the meaning of a specific chord symbol is learned, the chord can be played in any composition.
However, the same chord, played in different compositions, will be comprehended differently by a listener. The reason is that the comprehension of a chord depends on its context, i.e. the development of the music prior to the moment when the chord is played. One particularly important context variable is the key. For instance, the C major triad chord occurring in the C major key will not be comprehended the same as the C major triad chord occurring in the F major key. In the F major key, the C major triad chord builds tension, while in the C major key it relaxes tension (the building or releasing of tension by the harmony will be further explained in chapter Cadences and phrases). Thus, we need a notation that is more suitable for the task of analysis and composition and this is the subject of the next chapter.
In this book, chords are annotated above a staff while harmony is annotated below a staff. In all the examples that follow, for instructional purposes, we shall annotate both the chords and the harmony. In practice, usually only one of these two is annotated.
In chapter Key of passage we learned that one or more change of the key can happen during a composition. Thus, we can divide a composition into the passages that are written in the different keys. The currently observed chord will then belong to one of these passages and the key of this passage will be called the current key. Thus, the current key is the key which is in effect when the currently observed chord happens. When annotating the harmony of a composition, we must annotate the current key only at the beginning of the composition and at the each change of the tonality (modulation). However, in this chapter and in some other chapters, where we examine individual chords, we annotate the current key before each chord. A letter in the upper case is used to annotate a major key, while a letter in the lower case is used to annotate a minor key. The colon symbol is used to separate a key from the rest of a harmony annotation. For instance, C: annotates the beginning of a passage in the C major key, while a: annotates the beginning of a passage in the A minor key.
We already know that when we are annotating chords, we annotate chord roots by using note names. When annotating harmony, chord roots are annotated with the scale degrees of chords, using the Roman numerals as explained in chapter Scale degrees of chords. From this it follows that when we transpose a composition, its chords annotation will change while its harmony annotation will not. That is, the harmony annotation is invariant to the key. This is a clear advantage of the harmony annotation over the chords annotation.
The harmony annotation uses the Roman numerals in the upper and lower case. The Roman numeral is in the upper case when the interval between the chord root and the chord third is the major third (like in the major chords, augmented chords, dominant chords and augmented-major chords). The Roman numeral is in the lower case when the interval between the chord root and the chord third is the minor third (like in the minor chords, diminished chords, half-diminished chords and minor-major chords).
When annotating harmony, the Roman numerals are appended with symbols that annotate the chord quality and inversion. These symbols are similar to those used when annotating chords. However, some differences exist. The biggest difference is in the usage of the so-called figured bass notation. The figured bass notation uses Arabic numerals that are written one above the other. This will be explained in chapter Figured bass. When annotating harmony, chords in the root position have at most one numeral. For them, no numeral means a triad chord, 7 means a seventh chord while 9 means a ninth chord. This is quite similar to annotating chords. However, for chord inversions, more than one numeral can appear.
In the next chapters, annotating harmony for chords in the root position will be explained first.