The Moves

Eleven things a chord can do in a key, each declared once as a rule the reader checks against the chords either side of it, and each worked through the same corpus of lines.

On this site a move is something a single chord does in the key a line is read in, written down as a rule the reader can check without judgement. Most rules look at one chord: its root, how far that root sits above the tonic, whether its triad is major or minor, and whether any of its notes fall outside the key. Some look at two chords, because a V of V is only a V of V when the chord after it is the key's V. One looks at three chords in a row. The page for each move writes its rule out as steps, so you can check any line against it with a pencil.

Where the rules come from

Every move is declared from a published source that was read for this site, and each source prints its own example: a numeral, a chord spelled note by note, or a short line. The build parses each of those examples and fails if the declared rule does not accept it. A move that could not be matched against a source is not declared at all.

When two rules could claim a chord

Some chords fit more than one description. Eb in C major is a borrowed bIII and also a chord a third away from the tonic; E before Am is a V of vi and also a third away. The reader follows the order Sorce gives in the source for the chromatic mediant: borrowing is ruled out first, then a chord leaning on the one after it, and only then is a chord called a chromatic mediant.

The corpus

Every move is worked through the same set of lines. Some are printed by a source and read exactly as printed; the rest are test cases written for this site, each to show one thing, and labelled that way. Every move fires in at least one line, and two of the lines are controls in which nothing fires at all.

The eleven moves, counted

Eleven moves are declared, and across the corpus they fire 20 times. Every one fires at least once; a rule that fired nowhere would be a claim, not a reading, and the build fails on one.

Every declared move, what spots it, and how often it fires across the eighteen corpus lines.
Move Spotted as Looks at Fires
The minor iv a minor chord on the fourth degree of a key whose own tonic chord is major one chord 1
The flat three a major chord a minor third above the tonic of a key whose own tonic chord is major one chord 1
The flat six a major chord a minor sixth above the tonic of a key whose own tonic chord is major one chord 3
The flat seven a major chord a whole tone below the tonic, in a major key whose own scale does not hold it one chord 2
bVI–bVII–I two major chords a minor sixth and a minor seventh above the tonic, in that order, then the major tonic chord three chords 2
V of V a major or dominant-seventh chord on the second degree, outside the key, followed by a chord on the fifth degree two chords 1
V of vi a major or dominant-seventh chord on the third degree of a major key, followed by the minor chord on the sixth two chords 1
The deceptive arrival a major V followed not by the tonic but by the chord on the sixth degree: vi or bVI in a major key, and the major bVI in a minor one two chords 3
The chromatic mediant a chord of the tonic’s own quality whose root is a third away, next to the tonic chord, neither borrowed from the parallel key nor resolving down a fifth two chords 3
The dominant a tritone away a dominant seventh chord whose root is a semitone above the chord it moves to two chords 1
The major V in a minor key a major or dominant-seventh chord on the fifth degree of a minor key, whose natural scale holds only a minor v one chord 2

When two keys tie

The key detector scores a line and reports a tie as a tie. When it does, every page here names each tied key and reads the line in the first of them by this order:

  1. The network’s two keys come first: a reader asking what key a line is in means major or minor, so a mode is named only when it outscores both
  2. Then a reading whose tonic is the chord the line ends on — the stronger of the two tonic signals, because a cadence ends at home
  3. Then a reading whose tonic is the chord the line starts on
  4. Then the remaining modes in church order
  5. And finally tonic order from C, which means nothing and is said so

How a key scores

  • +1: every tone of the chord, a slash bass included, is a note of the key's scale.
  • -1: at least one tone is not — reported with the outside tones, never hidden.
  • +1: the first chord read fits and stands on the tonic: a line usually starts at home.
  • +1: the last chord read fits and stands on the tonic: a cadence ends at home.

The corpus: eighteen lines

Eight of the lines are printed by a published source and are read here exactly as printed; the other ten are test cases written for this corpus, each to show one thing, and are labelled that way.

The corpus: every line the moves are worked through, the key each is read in, and what fires.
Line Read in Moves Line from
C Bb Ab Bb C C mixolydian bVI bVI–bVII–I as printed in Borrowed chord, “Common borrowed chords” (Wikipedia)
Dm Bb7 C C major (tied) bVII as printed in Borrowed chord, “Common borrowed chords” (Wikipedia)
Ab Bb C C mixolydian (tied) bVI bVI–bVII–I as printed in The Flat VI-Flat VII-I Cadence (StudyBass)
C F G C C F G Am C major (tied) deceptive as printed in The Flat VI-Flat VII-I Cadence (StudyBass)
C E C C major (tied) chromatic mediant as printed in Chromatic mediant (Wikipedia)
C A C C major (tied) chromatic mediant as printed in Chromatic mediant (Wikipedia)
C Ab C C major (tied) bVI as printed in Chromatic mediant (Wikipedia)
Am Cm Am A minor (tied) chromatic mediant as printed in Chromatic mediant (Wikipedia)
C F Fm C C major (tied) minor iv constructed test case
C Eb F C C major (tied) bIII constructed test case
C Em F G C Bb C C major bVII constructed test case
C F D7 G7 C C major V/V constructed test case
C E7 Am F G C C major V/vi constructed test case
C F G Am F G C C major deceptive constructed test case
Am Dm E7 F Dm E7 Am A minor (tied) deceptive major V major V constructed test case
C Dm G7 Db7 C C major bII7 constructed test case
C Bb F C C mixolydian none constructed test case
C Am F G C C major none constructed test case

Read one move

The Minor iv

A minor chord where the key expects a major one on its fourth degree — the lowered sixth is the note that marks it.

fires 1 time in the corpus

The Flat Three (bIII)

Eb major in the key of C: a major chord on the lowered third, with two of its notes from the parallel minor.

fires 1 time in the corpus

The Flat Six (bVI)

A major chord on the lowered sixth degree: Ab in C major, with two of its three notes from outside the key.

fires 3 times in the corpus

The Flat Seven (bVII)

A major chord a whole tone under the tonic — a move in a major key, and the mode’s own chord in mixolydian.

fires 2 times in the corpus

bVI–bVII–I

Two major chords climbing by whole tones into the tonic — Ab, Bb, C in C — read as one run.

fires 2 times in the corpus

V of V

A major II, or II7, that goes straight to V — D or D7 before G in the key of C.

fires 1 time in the corpus

V of vi

A major III, or III7, that lands on vi — E or E7 before Am in the key of C.

fires 1 time in the corpus

The Deceptive Arrival

A V that lands on the sixth degree instead of the tonic — G to Am in C, E to F in A minor.

fires 3 times in the corpus

The Chromatic Mediant

E or A major beside C major: a same-quality chord a third away, after every simpler reading is ruled out.

fires 3 times in the corpus

The Dominant a Tritone Away (bII7)

A dominant seventh that slides down a semitone into its target — Db7 to C, a tritone from G7.

fires 1 time in the corpus

The Major V in a Minor Key

E or E7 in A minor: the major V a minor key uses, with the raised seventh its own scale does not hold.

fires 2 times in the corpus