Music Fundamentals III: Triads & Seventh Chords

Name: AP Music Theory Unit 3: Music Fundamentals III: Triads & Seventh Chords
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2 lessons · 28 min

What this unit covers

The topics below follow the published Music Theory course framework for Unit 3. Music Theory publishes no per-unit weighting, so there is no percentage to chase here.

TriadsSeventh chordsInversionsFigured bass

Lessons in this unit

Intervals: Size & Quality14 min · 3 objectivesMeasure an interval’s size by counting letter names inclusively · Assign quality — perfect, major, minor, diminished, or augmented · Invert an interval and predict the resulting size and quality
Triads & Seventh Chords14 min · 3 objectivesBuild major, minor, diminished, and augmented triads from stacked thirds · Identify a chord’s root, third, and fifth in any inversion · Construct and name the five common seventh-chord qualities

Formulas in Unit 3

Half steps per interval quality

m2=1 · M2=2 · m3=3 · M3=4 · P4=5 · TT=6 · P5=7 · m6=8 · M6=9 · m7=10 · M7=11 · P8=12

Count half steps between the two pitches, then match the number and the letter-name size to this table. Inversions of any pair sum to 12 half steps (and size numbers sum to 9).

Chord-quality recipes

Major=M3+m3 · minor=m3+M3 · dim=m3+m3 · aug=M3+M3 || seventh chord = triad + (M7, m7, or d7)

Read a triad from its two stacked thirds; add the top third to get the seventh. Figured bass for triads: root=(blank), first inv=6, second inv=6/4.

What examiners penalize here

Memorize the two ways the tritone appears: **augmented fourth (fa–ti, e.g. F–B)** and **diminished fifth (ti–fa, e.g. B–F)**. Spotting the tritone between scale degrees 4 and 7 is essential for identifying the dominant chord and voice-leading its resolution.
Distinguish the two diminished sevenths by the top interval: **half-diminished (ø7)** has a **minor** seventh, **fully diminished (°7)** has a **diminished** seventh (a stack of three minor thirds). In major keys the viiø7 is common; the fully diminished °7 usually signals a minor key or a secondary function.

Practice Music Theory

Our practice bank is drawn from across the whole course rather than filtered to one unit, which is closer to how the exam asks anyway — it will not tell you which unit a question is testing.

24 practice questionsEvery one with a written explanation FRQ trainerWritten answers scored against the rubric Music Theory study guideAll units, weights and score data in one place All 8 Music Theory unitsThe full course

Questions about this unit

How much of the AP Music Theory exam is Unit 3?

The Music Theory course framework does not publish a per-unit weighting, so there is no percentage to quote for Unit 3 and anyone who gives you one is guessing. Spread your time by where your own errors are instead.

What topics are covered in Music Theory Unit 3?

Music Fundamentals III: Triads & Seventh Chords covers Triads, Seventh chords, Inversions and Figured bass.

How should I study Music Theory Unit 3?

Read the 2 lessons below first — about 30 minutes — then work practice questions on these topics. Finish with practice questions and read the explanation for every one you get right by elimination as well as the ones you miss.

All 8 units of AP Music Theory

Unit names, topics and exam weights follow the published College Board course framework for AP Music Theory. AP® is a trademark registered by the College Board, which does not endorse this site.