Reading a Progression That Moves

Time to use all of it on something real. This track is a blues in G major, and the chords in it are G, G7, C, C sharp diminished, E, A7 and D7.

Start where the first theory path told you to: work out which chords belong. The key of G major gives G, A minor, B minor, C, D, E minor and F sharp diminished. Checking the list against that, only two of the seven chords are plainly diatonic — G and C, the I and the IV. Five are not. A year ago that would have looked like a mess. Now every one of them has a name.

G7 is the I chord as a dominant seventh. Strict major-key theory forbids it, and lesson four explains it: this is G Mixolydian, with a flattened seventh, which is the normal harmonic world of a blues. The F natural inside that chord is a feature of the style, not a mistake.

D7 is the straightforward one. D is the fifth degree of G, so D7 is the V chord, exactly where lesson one said the key's only dominant seventh should be.

A7 is a secondary dominant. A minor is the ii chord of G; an A major seventh chord is not in the key. It is there because A is a fifth above D, so A7 is the dominant of D — five of five, written V/V. It exists to make the D7 arrive properly.

E is the same trick one step further back. E is a fifth above A, so E sets up the A7, which sets up the D7, which resolves to G. That is the chain from lesson five: four chords, each one the dominant of the next, walking down in fifths all the way home.

Which leaves C sharp diminished, and it is not a mystery either. It sits between the C chord and the D chord, and its root is one semitone above C and one semitone below D. It is a passing chord — a diminished seventh dropped between two chords a tone apart, purely to give the bass a chromatic step rather than a jump. Diminished chords are unstable enough that they cannot function as a destination, so when you meet one, look at what is on either side of it; it is almost always a bridge.

So the whole list resolves to: the I chord in its bluesy dominant form, the IV, a passing chord, and a chain of dominants leading back to the tonic. No chord is unexplained, and nothing about it is unusual.

The track itself, in G major. Follow the chord changes as they pass and try to name each one's function rather than just its letter.

That is the skill this path was for. Naming chords is the beginner's job and you could already do it; saying what each chord is doing, and why a foreign one sounds right, is what lets you learn songs faster, transpose them, and write your own.

A method to keep using. Work out the key. List the diatonic chords. Mark anything that is not on the list. For each outsider ask three questions in order: is it a dominant pointing at the chord that follows it, is it borrowed from the parallel minor, or is it a passing chord between two neighbours? Nearly everything in popular music answers to one of those three.

From here, Jazz Guitar: Your First Changes puts the ii-V-I motion from lesson one to work across a whole repertoire, and Blues Soloing Beyond the Box takes the Mixolydian material of lesson four into actual soloing.