Functional theory

Chords by their job

The page Diatonic chords introduces functional theory in its section on the three functions: not every degree weighs equally. Tonic, subdominant and dominant carry the harmony, and the basic progression T – S – D – T is the germ of almost every cadence.

Substitutes

According to the same page, the other degrees are not gap-fillers but substitutes for the three main functions. Because they share two notes with their main function, they can take over its role and bring a softer colour with them. The tonic parallel (Tp, the relative chord of the tonic, degree vi) stands in for the tonic: the move V – vi instead of V – I is the classic deceptive cadence. The subdominant parallel (degree ii) stands in for the subdominant: the progression ii – V – I is ubiquitous in jazz. The tonic counter-relative (Tg, degree iii) is a mediant: it lies close to the tonic and colours it.

The substitute principle is international, but the labelling differs. The letters T, S, D, Tp and Sp are Riemann's and are used above all in German-speaking countries. In English-language teaching the same idea is usually written with Roman numerals: vi is called the submediant and is described as a tonic substitute, ii as the supertonic.

Hearing functions

The article One pattern predicts the chords of almost any pop song shows the functions in everyday use: the tonic is rest, the dominant creates a pull back, the relative minor brings a clouding, the subdominant opens up the space. Played as a circle this gives a movement that never quite arrives.