Third inversion is the arrangement of a seventh chord with the chordal seventh in the bass, labeled with the Arabic numerals 4/2 (e.g., V4/2). It only exists for seventh chords, since triads have just three notes and three possible bass positions.
Third inversion means the chordal seventh of a seventh chord is the lowest sounding note. That's the note a seventh above the root. So in a G7 chord (G-B-D-F), third inversion puts F in the bass. The CED is explicit about this in PIT-2.D.1: seventh chords "have the potential for a third inversion in which the chordal seventh appears in the bass." Triads can't do this. With only three notes, a triad runs out of inversions after second inversion. The seventh chord's fourth note is what unlocks this extra position.
In Roman numeral analysis, you label third inversion with the figures 4/2 (sometimes written 6/4/2). Those numbers come from figured bass. They describe the intervals above the bass note: a fourth up to the root and a second up... wait, actually a fourth and a second above the bass land you on the root and the third of the chord. The full stack above the bass is 6-4-2, and 4/2 is the shorthand. So a dominant seventh in third inversion is V4/2. Because the bass note is the chordal seventh, it carries a strong tendency to resolve down by step, which is why V4/2 almost always moves to I6 (first-inversion tonic).
Third inversion lives in Unit 3: Music Fundamentals III - Triads and Seventh Chords, specifically Topic 3.5 (Seventh Chord Inversions and Figures). It directly supports learning objective 3.5.A, which asks you to identify seventh chords using Roman and Arabic numerals that show the root's scale degree, the chord quality, and the bass note. Third inversion is the piece of that objective that's unique to seventh chords, so it's a natural thing for the exam to probe. It also sets up everything you do later with voice leading. The chordal seventh in the bass must resolve down by step, and that rule drives the V4/2 to I6 progression you'll see constantly in part-writing and harmonic analysis.
Keep studying AP Music Theory Unit 3
Visual cheatsheet
view gallerySeventh Chord (Unit 3)
Third inversion only exists because seventh chords have four notes. The fourth note, the chordal seventh, is exactly the note that ends up in the bass. No seventh, no third inversion.
Second Inversion (Unit 3)
Second inversion puts the fifth in the bass (figures 4/3 for seventh chords). It's the position right before third inversion in the sequence root, first, second, third, and it's the one most often mixed up with 4/2 on figure-identification questions.
Root Position (Unit 3)
Root position is the starting point of the whole system, with the root in the bass and a figure of 7. Think of inversions as rotating the chord: each inversion moves the next chord member down into the bass until the seventh lands there in third inversion.
V-6/5 chord (Units 3-4)
V6/5 is the dominant seventh's first inversion, and it pairs with V4/2 as the two most exam-relevant dominant inversions. Both contain the same tendency tones, but V4/2's bass note (the seventh) forces resolution to I6 instead of root-position I.
Multiple-choice questions love the "which note is in the bass?" angle. You'll see stems like the ones in the inversion sequence: root position has the root lowest, first inversion has the third, second inversion has the fifth, and third inversion has the chordal seventh. Expect to do this in both directions, naming the bass note from a figure (4/2 means seventh in the bass) and naming the figure from notated music. Aural questions can ask you to identify the bass note of a played seventh chord. On the written FRQs, third inversion shows up in figured bass realization and part writing, where a 4/2 figure tells you to build the chord above a bass note that is the seventh, then resolve that bass down by step (V4/2 to I6 is the classic move). Getting the figure wrong, like writing 4/3 instead of 4/2, costs points fast.
Second inversion puts the FIFTH of the chord in the bass and uses the figures 4/3 for a seventh chord. Third inversion puts the chordal SEVENTH in the bass and uses 4/2. A quick check: in G7 (G-B-D-F), second inversion has D in the bass, third inversion has F. The figures are also easy to swap under time pressure, so memorize the descending pattern 7, 6/5, 4/3, 4/2.
Third inversion means the chordal seventh of a seventh chord is in the bass, and it's labeled with the Arabic numerals 4/2.
Only seventh chords have a third inversion, because triads run out of notes after second inversion (PIT-2.D.1).
The full inversion sequence for seventh chord figures is 7 (root position), 6/5 (first), 4/3 (second), and 4/2 (third).
Because the bass note is the chordal seventh, it must resolve down by step, which is why V4/2 typically resolves to I6.
In a G7 chord (G-B-D-F), third inversion puts F in the bass, with G, B, and D stacked somewhere above it.
Third inversion is the position of a seventh chord where the chordal seventh is the lowest note, labeled with the figures 4/2. For G7 (G-B-D-F), that means F is in the bass.
No. The fifth in the bass is second inversion (4/3). Third inversion puts the chordal seventh in the bass, which is exactly how the AP CED defines it in PIT-2.D.1.
Second inversion has the fifth in the bass and uses the figures 4/3, while third inversion has the seventh in the bass and uses 4/2. In G7, that's D in the bass versus F in the bass.
No. A triad has only three notes (root, third, fifth), so its inversions stop at second inversion. Third inversion requires a fourth chord member, the chordal seventh, which only seventh chords have.
The bass note of V4/2 is the chordal seventh, a tendency tone that must resolve down by step. Stepping down lands the bass on the third of the tonic chord, producing I6 instead of root-position I.