Functional harmony is harmony with a purpose.
Functional harmony combines the main features of counterpoint with those of chordal harmony. It derives its guidelines for melody construction, consonance and relative motion from counterpoint, and its rules for chord construction and progression from chordal harmony.
The function in functional harmony means purpose, in the sense of musical purpose not social purpose. The function, or musical purpose, of functional harmony is to promote tonality. This is why functional harmony is also called tonal harmony and the two terms can be used interchangeably. Functional harmony is also called diatonic harmony, common practice harmony or tonal counterpoint.
Every note and chord in functional harmony has a function. The function of a note is determined by its position in the scale. The function of a chord is that of its root note.
Functional harmony is tertian in nature. Chords are constructed from thirds and the triad is the most important and widely used chord of them all.
Functional harmony is normally written in four parts, occasionally in three. The four parts typically consist of the three notes in a triad with one of the notes doubled. The parts are in SATB voicing and the terms soprano, tenor, alto and bass are used to describe the individual parts irrespective of whether the music is vocal or instrumental. Chorale is a common term for functional harmony in four parts.
This section starts by looking at the function of a triad and how and why it is classed as either a primary triad, whose primary function is to promote tonality, or a secondary triad, a triad that plays a supporting role.
Certain types of parallel motion, are banned, namely, parallel fifths and octaves.
Voice leading, an unusual phrase, describes the set of principles and procedures used in functional harmony to connect chords together.
Major harmony and minor harmony are the pithy terms used to describe the process of writing functional harmony in a major key and a minor key respectively. Functional harmony uses only major or minor scales, it does not use modes.
A cadence is a chord progression that marks the end of a section.
Functional modulation looks at how to develop a harmony by changing key.
The section ends with embellishment which provides a decorative role for melody notes that do not form part of a chord.