Why do composers use all those flats and sharps, let alone the weird x’s? Understanding this question can help you both as you play music and as you write it.
To show how this works, let’s first explore the 4 sources of chromaticism in common-practice tonality.[1. At least, I parse them that way. The fourth could be subsumed into the other three, but I think it is a unique enough cross-section of their features to merit its own category.]
Four Kinds of Chromaticism
1) Structural Chromaticism
“Structural Chromaticism” occurs at the boundaries between diatonic collections.[1. major or minor scales that don’t start on the same note.] Between tonic and dominant (e.g., the keys of A and E) it entails only raising the fourth scale degree (D) to become the seventh scale degree[2. i.e., the “leading-tone”] in the new key (D-sharp). More distantly related keys may involve more chromatic notes, but the effect is the same: these notes merely represent the overthrow of one diatonic collection (say, CDEFGAB) by a different diatonic collection (say, C#DEF#GAB).
2) Situational Chromaticism
“Situationally chromatic” notes reinforce local voice leading[3. Voice leading is the way strands of music move up or down by step to give the music its sense of direction.] but don’t represent a change in diatonic collection.[4. Often because they arise in passages without a stable diatonic collection.] This category includes
- Neapolitan sixth chords
- Augmented sixth chords
- chains of dominants (whether M, d, Mm7, dm7 or dd7)
- chains of dominant-tonic resolutions (again, regardless of the dominant’s quality)
The first two strengthen voice leading to the dominant. The third, sequences, uses chromaticism to preserve the intervals in whatever pattern it’s repeating. The last two transpose the dominant function to different pitch levels, often on the way to a modulation. (In other words, the last two serve increase suspense: “Where are we going to stop?”)
3) Coloristic Chromaticism
Coloristic chromaticism[4. If you’ll forgive the redundancy of the phrase, because “chromatic” means “color.”] is merely decorative, such as chromatic embellishing tones or chord extensions. Little 18th-century chromaticism falls into this category. It became more prominent in 19th- and 20th-century music.
4) Modal Chromaticism
These chromatic notes arise from borrowing notes between parallel major and minor. It includes chords like flat-VI and iv in major or IV in minor. In most forms, one could safely categorize this as a kind of ”coloristic” only that the color source has a stronger structural basis (the parallel scale).
Sometimes modal chromaticism takes on a “situational” function, such as to intensify vii7 in major (by replacing the half-diminished chord in major with its fully diminished analogue) or for the voice leading of 6–flat-6–5 (in some inversion of subdominant harmony leading to tonic) also in major.
How This Helps in Performance
Identifying what kind of chromaticism occurs in a particular passage gives you clues about a note’s meaning — and thus how you play it. For instance,
- Structural chromaticism tends to point to local modulations. You should be shaping your phrases in this direction.
- Situational chromaticism tends to point to larger arrivals (e.g., between parts of a sonata form), either because it intensifies the dominant (saying in effect “this dominant is more important than the others”) or because it has created suspense by preventing the music from settling into a local key. Again, this suggests the direction in which you should shape your phrases.
- Coloristic chromaticism suggests various responses in rubato, articulation or dynamics.
These are, of course, general interpretations, but they show the kinds of information provided by identifying the source of a chromatic inflection.
How This Helps in Composition
When writing using diatonic scales or modes, knowing these different inflections helps you make a variety of choices:
- It allows you to manipulate the meanings of your pitches. A note no longer needs to use only its basic diatonic function. A coloristic G-sharp in one passage can become a structural one in the next. Likewise, G-sharp functioning structurally as supertonic can become one functioning as dominant. This kind of reinterpretation adds depth of meaning to what you write.
- It allows you to make shrewd choices about why you choose the chords you do. For instance, you will know why borrowing flat-submediant from minor into major won’t affect the form as much as using that same chord as part of a chain of dominants.
- Likewise, it allows you to use color more freely because you’ll be able to separate it from the underlying structural implications.
Granted some of this knowledge has to do with voice-leading but that’s another post for another day.
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