Harmony starts here. Build the four triad qualities by stacking thirds, label every diatonic chord with Roman numerals, read figured-bass inversions, and construct the five kinds of seventh chords — the vocabulary for everything in Units 4–7.
Six ways to master Unit 3 — pick whichever fits how you like to study.
Five topics from the College Board CED, in order.
Unit 3 is where individual pitches become chords. You'll stack thirds to build the four triad qualities (major, minor, diminished, augmented), then add a fourth note to make seventh chords. You'll label chords two ways: with Roman numerals that show a chord's scale degree and quality, and with figured bass that shows which chord tone sits in the bass.
Unlike most AP courses, the College Board does not assign a percentage of the exam to each unit — the exam is weighted by section (45% multiple choice, 45% free response, 10% sight-singing). But Unit 3 is essential: the harmony and voice-leading of Units 4–7 all assume you can spell and label any triad or seventh chord instantly.
Unit 3 develops two of the four AP Music Theory Big Ideas: