Second Inversion in AP Music Theory

Second inversion is a chord position in which the fifth of the chord is the lowest (bass) note, labeled with the figures 6/4 for triads and 4/3 for seventh chords, because those numbers name the intervals sounding above the bass.

What is Second Inversion?

Every chord has a root, but the root doesn't have to be on the bottom. When you stack a chord so its fifth is the lowest-sounding note, you've got second inversion. The figured bass numbers come straight from the intervals above that bass note. For a triad in second inversion, the other chord tones sit a sixth and a fourth above the bass, so you write 6/4. For a seventh chord in second inversion, the full interval stack is 6/4/3, abbreviated to 4/3.

Think of inversions as the same chord wearing different shoes. The pitches and the Roman numeral root stay the same, but the bass note changes the chord's stability and how it wants to move. Second inversion is the least stable position for a triad because of that fourth above the bass, which is why 6/4 chords show up in specific, controlled situations rather than as freestanding harmonies. Per the CED's seventh-chord framework (PIT-2.D.1 covers the full inversion ladder, all the way to third inversion with the seventh in the bass), second inversion is one stop on a four-position sequence you need to label instantly: root position (7), first inversion (6/5), second inversion (4/3), third inversion (4/2).

Why Second Inversion matters in AP Music Theory

Second inversion lives in Topic 3.5 (Seventh Chord Inversions and Figures) in Unit 3, where learning objective 3.5.A asks you to identify seventh chords with Roman and Arabic numerals showing root, quality, and bass note. If you can't decode 4/3 on sight, you can't do 3.5.A. It also threads into Topic 5.2 (The vi Chord) in Unit 5, where learning objective 5.2.A has you describe harmonic function in performed and notated music. Inversion changes a chord's bass line and stability, which feeds directly into function questions, like whether a vi chord is acting as a tonic substitute or a weak predominant (PIT-2.J.1). Across the whole harmony sequence (Units 4-7), every progression you write or analyze gets labeled with these figures, so second inversion is foundational vocabulary, not a one-topic detail.

How Second Inversion connects across the course

Root Position (Unit 3)

Root position is second inversion's anchor point. In root position the root is the bass and the chord is maximally stable; flip the fifth to the bass and you trade that stability for tension that wants to resolve. Exam questions love asking you to identify which chord member is in the bass for each position.

Inversion (Unit 3)

Second inversion is one rung on the inversion ladder. Triads have two possible inversions, but seventh chords get a third one because the chordal seventh can also land in the bass (PIT-2.D.1). Memorize the seventh-chord sequence as 7, 6/5, 4/3, 4/2 and second inversion is always the 4/3 slot.

ii 6/5 chord (Unit 5)

Here's where students slip. The ii6/5 is a first inversion seventh chord, not a second inversion anything, even though 6/5 'sounds like' a fraction near 6/4. Seeing 6/5 next to 4/3 in real progressions forces you to keep the figure-to-inversion mapping straight.

Chord Function (Unit 5)

Inversion shapes function. The vi chord, for example, can substitute for tonic or act as a weak predominant (PIT-2.J.1), and what's in the bass affects how convincingly it does either job. A second-inversion voicing weakens a chord's footing, which changes how it behaves in a progression.

Is Second Inversion on the AP Music Theory exam?

Second inversion is mostly a multiple-choice and figured-bass-realization skill. Expect stems like "In second inversion, which note of a seventh chord is the lowest?" (answer: the fifth) and "What figures indicate a second inversion seventh chord?" (answer: 4/3, short for the 6/4/3 intervals above the bass). You'll also see it embedded in Roman numeral analysis questions, where a wrong inversion figure costs you even if you nailed the root and quality. On the part-writing FRQs, realizing figured bass means a 4/3 figure tells you exactly which chord member goes in the bass voice, so this term shows up in your answers even when the prompt never says "second inversion" out loud.

Second Inversion vs First inversion (6 / 6/5)

First inversion puts the third of the chord in the bass; second inversion puts the fifth in the bass. The figures are the giveaway. A triad is 6 in first inversion and 6/4 in second; a seventh chord is 6/5 in first inversion and 4/3 in second. Students mix up 6/5 and 6/4 constantly because they look similar on the page. Just remember the numbers literally count intervals above the bass, so they change every time the bass note changes.

Key things to remember about Second Inversion

• Second inversion means the fifth of the chord is the lowest note in the voicing.

• A second inversion triad is figured 6/4, and a second inversion seventh chord is figured 4/3 (short for 6/4/3).

• The figured bass numbers always name the intervals above the bass note, which is why the figures change with each inversion.

• Seventh chords have one more inversion than triads because the chordal seventh can also appear in the bass (that's third inversion, figured 4/2).

• Second inversion is the least stable triad position, so 6/4 chords appear in controlled contexts rather than as independent harmonies.

• Knowing inversions feeds directly into Unit 5 function analysis, since the bass note shapes how chords like vi behave in a progression.

Frequently asked questions about Second Inversion

What is second inversion in music theory?

Second inversion is a chord position where the fifth of the chord is the lowest note. A C major triad in second inversion has G in the bass, with C and E above it, and is labeled with the figure 6/4.

What does 6/4 mean in figured bass?

6/4 marks a second inversion triad. The numbers count the intervals above the bass note, so with the fifth in the bass, the root sits a fourth above and the third sits a sixth above.

Is 6/5 a second inversion chord?

No. 6/5 is a first inversion seventh chord, with the third in the bass. Second inversion of a seventh chord is figured 4/3. The full seventh-chord sequence is 7 (root position), 6/5 (first), 4/3 (second), 4/2 (third).

How is second inversion different for triads versus seventh chords?

Both put the fifth in the bass, but the figures differ because seventh chords have an extra note. A triad in second inversion is 6/4, while a seventh chord is 4/3 (abbreviated from 6/4/3).

Which note is in the bass in a second inversion seventh chord?

The fifth of the chord. For a G7 chord (G-B-D-F), second inversion puts D in the bass, and you'd label it V4/3 in the key of C.