Music Theory II — Chords & Progressions
Now we build. Chords are not memorized shapes — they are stacks of notes from a scale. Once you see how they are built and how they relate inside a key, you can understand, and even predict, almost any progression in popular music.
Concepts
An interval is the distance between two notes. Stack the 1st, 3rd, and 5th notes of a scale and you get a triad — a basic chord.
Every major key has 7 diatonic chords, and the pattern never changes: I ii iii IV V vi vii° — major, minor, minor, major, major, minor, diminished. In C that is C Dm Em F G Am B°.
The V chord (G in C) contains the leading tone and "pulls" back to I. That tension and release is the engine of most songs — and ii–V–I is the most common move in all of music.
Modes are the same scale started on a different note: play C major from D to D and you get D Dorian, a new flavor from the same seven notes.
Graduation
Pick any major key, build its I, IV, V, and vi chords from the scale, then find a song that uses them.