Jazz and Popular Practical Theory — From Chord-Scale to the Present

A Lineage Apart from Academism — “Usable Theory”

The 20th-century academic theories seen in Articles 7-9 (Schenkerian analysis, twelve-tone, set theory) were mainly for “analyzing works” and “constructing the avant-garde.” But an entirely different lineage grew in parallel — a practical theory that performers and improvisers of the field can “use right now.” Its greatest source was jazz, and then popular music.

Jazz Theory — Chord-Scale Theory

Jazz, while grounded in functional harmony since Rameau (Article 4), developed its own practical theory for improvisation:

• chord-scale theory — the correspondence “over this chord, you can improvise with this scale.” E.g., D Dorian over Dm7, G Mixolydian over G7. It bridges chord (vertical) and scale (horizontal)
• tensions — upper-structure notes such as 9th, 11th, 13th that add color to a chord
• two-five (II-V-I) — the most basic progression unit of jazz (the lineage of Riemann’s S-D-T, Article 6)
• modal jazz — after Miles Davis’s Kind of Blue (1959), a method of improvising at length over a mode rather than a chord progression. A partial departure from functional harmony

These are not analyses of “why it is beautiful,” but a practical map of “how to improvise.” They were honed as tools for split-second judgment in performance.

The Berklee Method — Standardizing Practical Theory

The theory systematized by Berklee College of Music (the Berklee method) became the world standard of jazz and popular practical theory:

• the notation of chord symbols (Cmaj7, Dm7, G7, etc.)
• correspondence tables of chord scales
• techniques of reharmonization (chord substitution)

These spread to music schools and self-learners worldwide and became the common language of modern popular-music production. If academic theory is for “reading and analyzing,” the Berklee method is theory for “playing and making.”

Popular Music Theory — Patterned Progressions

In J-pop and Western pop, stock chord progressions applying functional harmony loosely are shared as “types”:

• the canon progression — from Pachelbel’s Canon (I-V-vi-iii-IV-I-IV-V)
• the royal-road progression — IV-V-iii-vi (frequent in J-pop, the standard of wistfulness)
• the Komuro progression — vi-IV-V-I (swept 1990s J-pop)
• countless hits from four chords — the I-V-vi-IV loop is common to pop worldwide (there is even a famous parody video)

They function as a shared vocabulary among makers and listeners rather than theorists — “this progression is this emotion.” “You can make songs without knowing theory,” but these types implicitly inherit the legacy of functional harmony (Rameau → Riemann).

Neo-Riemannian Theory — the 19th Century Returns

On the academic side too there was a modern new development — Neo-Riemannian theory:

• a modern reconstruction of the 19th-century Riemann (Article 6)
• treats transformations between chords with a geometric diagram called the Tonnetz (tone network)
• effective for analyzing chromatic chord progressions hard to explain by function (frequent in late Romanticism, film music, game music)

A perspective that grasps music not by “arrival at the tonic” but by “smooth transformation from chord to chord.” That Riemann’s name revived 100 years later is an interesting circulation in theory’s history.

AI Composition — Theory as Computational Model

In the 21st century, music theory entered a stage of being implemented as a computational model:

• early automatic composition by Markov chains (the probability of the next note)
• modern deep-learning generative models — learning “theory” implicitly from a mass of pieces and generating new music
• acquiring statistical patterns of harmony and progression from data, without writing explicit theoretical rules

This added a third way — “learning” theory from data — to the “descriptive vs. prescriptive theory” (see the overview). 2500 years after Pythagoras found order in string ratios, the order of music is now also something a machine extracts statistically.

Looking Back Over 2500 Years

Let us look back over the history of music theory traced in this series, through the four threads:

1. Number vs. ear — beginning with Pythagoras vs. Aristoxenus, integrated by Helmholtz, reignited by the divergence of set theory and listening, and now with AI (statistics) offering a new answer
2. Notation — Guido’s staff made theory possible; chord symbols support practice
3. Melody → harmony — Rameau (1722) established the vertical logic; jazz and pop distilled it into practical knowledge
4. Temperament — the decision from just intonation to equal temperament enabled the freedom of all keys, modulation, and jazz

Music theory was not a monolithic “correct answer” but a chain of different answers, era by era, to the question “how do we grasp the order of sound?” And the question is still open — the music theory of the AI age is yet to be written.

Concluding the Series

In eleven articles, we have traced the 2500 years of music theory — Pythagoras’s number, Guido’s notation, Zarlino’s counterpoint, Rameau’s harmony, the decision of equal temperament, Riemann and Helmholtz, Schenkerian analysis, the twelve-tone, set theory, non-Western theory, and up to the practical theory of jazz and pop.

Read as a history of “ways of thinking” — how people have grasped the order of sound — sitting exactly between the sister series [The Lineage of Mathematics] (a history of abstract concepts) and [The Lineage of the Piano] and [The Lineage of the Violin] (a history of instruments as things) — one comes to see music as an enterprise at the intersection of mathematics, physics, and sensibility.