Harmonic syntax concerns the norms or principles according to which harmonies (i.e., chords) are placed into meaningful successions. In Western classical music (pop/rock harmony is covered separately), harmonic syntax is closely tied to phrase structure. Harmony is not the only musical characteristic that contributes to the building of musical phrases. However, certain chords and chord progressions tend to appear in beginnings, middles, and ends of phrases. Thus the function of a chord concerns not only the notes that belong to it and which chords tend to precede and follow it, but where it tends to be employed in the course of a musical phrase.
You may already be familiar with one method of studying harmonic syntax, a root-oriented system that labels triads and seventh chords according to the scale degree of the root using Roman numerals. We will use these from time to time (and almost exclusively in our study of pop/rock music). However, for classical music, especially keyboard music of composers like Mozart, Haydn, Beethoven, and their contemporaries, we will use another system called functional bass.
The details of functional bass theory were largely put together in the last decade or so by Ian Quinn (Yale University). However, the system is not entirely new. It is based on older theories of harmony from figures like Jean-Phillipe Rameau, Hugo Riemann, and Allen McHose. The theory is based on five fundamental principles:
The syntactic properties of these functions will be covered elsewhere. What follows simply explains how to determine the function of a chord and provide a basic, uninterpreted functional bass label to a triad or seventh chord.
Each of the three harmonic functions—tonic (T), subdominant (S), and dominant (D)—have characteristic scale degrees. Tonic's characteristic scale degrees are 1, 3, 5, 6, and 7. Subdominant's characteristic scale degrees are 1, 2, 3, 4, and 6. Dominant's characteristic scale degrees are 2, 4, 5, 6, and 7.
Quinn (in a manner similar to Daniel Harrison) further distinguishes these scale degrees, using the categories of functional triggers, functional associates, and functional dissonances. These categories differentiate between scale degrees more or less characteristic of a function, and they help us understand the functional properties of chords whose scale degrees belong to more than one function, as well as how certain notes behave within a chord.
|T||1 and 3||5 and 6||5 (if 6 is also present) and 7|
|S||4 and 6||1 and 2||1 (if 2 is also present) and 3|
|D||5 and 7||2||4 and 6|
In terms of moveable-do solfège:
|T||do and mi/me||sol and la/le||sol (if la/le is also present) and ti/te|
|S||fa and la/le||do and re||do (if re is also present) and mi/me|
|D||sol and ti/te||re||fa and la/le|
To determine the function of a chord, find the function that includes all the scale degrees of a chord (irrespective of chromatic alterations). If more than one function contains all the scale degrees, take the function with the most triggers in the chord.
There is one exception to this (for now): a chord with scale degrees 6, 1, and 3 is a special kind of tonic chord, called a destabilized tonic. It's functional label is Tx, rather than T.
A chord's uninterpreted functional bass label is its function (T, S, D, or Tx) followed by the Arabic numeral for the scale degree of its bass note. A tonic chord with do in the bass is T1. A dominant chord with ti in the bass is D7. If the bass note is chromatically altered, use a + or – to denote raised or lowered (la and ti in minor do not count, since le, la, te, and ti all belong to minor), and if there is a chromatically altered note anywhere in the chord, put the functional bass symbol inside square brackets: [S6], [S+4], [T–7], etc.
See the resource on harmonic syntax for interpreted functional bass analysis.