The simplest form of keyboard-style writing is basso continuo (It. for "continuous bass" or "thoroughbass"). Basso continuo writing is essentially a chordal version of first-species counterpoint. Instead of composing a single line above a cantus firmus, one composes a succession of chords (performed in the right hand) above a bass line (performed in the left hand). Basso continuo writing, also referred to as realizing a figured bass, gives no consideration to melody, only to the use of proper chords and the smoothest voice-leading possible.
In any keyboard-style writing, there are four voices: the bass line (which is usually provided in basso continuo style), and three upper voices: the melody or soprano, the alto, and the tenor (from highest to lowest). Since all three must be played by a single hand, they should never span more than an octave.
When choosing the notes to place in the upper voices above a figured bass, use the bass and figures to determine the pitch classes present in the chord. (When realizing an unfigured bass, you must determine appropriate figures before realizing.) If the chord is a four-note chord, use each chord member once, including the bass (exceptions will be noted later). If a chord has three pitch-classes (a triad, for instance), use each pitch-class once, and "double" one of them according to the following principles:
In basso continuo style, if the chord is properly voiced (correct pitch classes and correct doublings), two key principles of voice-leading will ensure good counterpoint between the voices most of the time:
In some cases, these rules cannot be followed absolutely (such as when a functional dissonance must be resolved, or when a melody makes it impossible—two cases to be considered later). In all cases, observe the following:
Strict keyboard-style voice-leading involves the composition of two primary musical lines—the melody and the bass line. The inner voices are secondary and serve largely as harmonic "filler." All principles of good basso continuo voice-leading hold for melodic keyboard-style writing. However, because of the inclusion of a melody, several additional principles of composition must be observed.
The outer voices (melody and bass) draw the most attention, and therefore they should make good counterpoint with each other. The melody should largely follow the principles of composing a cantus firmus or a first-species counterpoint line. In a strict keyboard-style melody that means:
These melodic constraints may make following the law of the shortest way and contrary/oblique motion with the bass difficult, and at times impossible. When that happens, be very careful not to compose voice-leading errors such as forbidden parallels.
In general, if you follow the figures, double the correct chord tone, move the upper voices as little as possible and in contrary or oblique motion to the bass, and take special care when the melody makes the latter impossible, your voice leading will sound smooth and will be fairly easy to perform. Those are the goals of strict keyboard-style voice-leading.
The melody always has an upward-pointing stem. Alto and tenor share a downward-pointing stem. If the alto and tenor share a note, that note receives a single downward-pointing stem. If melody and alto share a note, that notehead is double-stemmed.
Ti (not te) and le (not la) are tendency tones.
Generally speaking, when ti appears in an upper voice of a dominant-functioning chord, it should be followed by do in the same voice upon change of function (to T, Tx, or S).
Likewise, when le appears in an upper voice of a subdominant-functioning chord, it should be followed by sol in the same voice upon change of function.
Exceptions to these tendencies include:
Following are the scale degrees which act as dissonances for their respective functions:
| function | dissonances |
|---|---|
| T or Tx | 7, 5 when 6 is also present |
| S | 3, 1 when 2 is also present |
| D | 4, 6 |
When one of these scale degrees is present in a chord with the corresponding function, the dissonant scale degree should resolve down by step over the next change in function. In strict keyboard style, these functional dissonances should behave like one of the three dissonance types of species counterpoint: a passing tone or neighbor tone dissonance that is approached by step, or a suspension dissonance that is approached by a common tone. The suspension type is preferred.
Once a functional dissonance is introduced, it must be resolved down by step in the same voice when the function changes. The dissonance can also be transferred to another voice before resolution—for instance, if there are multiple chords in a row exhibiting the same function, a dissonance that appears in the alto can be transferred to the tenor in the following chord, and then resolve in the tenor when the function changes. (It is more typical, and smoother sounding, to transfer dissonances between inner voices or from an inner voice to an outer voice than from an outer voice to an inner voice. Once a dissonance appears in the melody or bass, it tends to resolve in that voice.)
Functional dissonance resolutions often cause conflicts with other principles of voice leading. Except in special cases such as schemata (standard patterns that are common enough to sound appropriate, even if they follow different rules), the functional dissonance resolution takes precedence over other principles such as the law of the shortest way, contrary motion with the bass, and preferring common tones and steps to melodic leaps. A dissonance resolution is never an excuse for illegal parallels, and only rarely can justify non-standard doublings.
Realizing a thoroughbass in strict basso continuo style from Kris Shaffer on Vimeo.