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A chord's inversion is determined by which note is in the bass: root position has the root in the bass, first inversion has the third in the bass, second inversion has the fifth in the bass. Different inversions create different voice-leading possibilities and affect the harmonic motion and smoothness of chord changes. Inversion symbols (figured bass) indicate the intervallic content above the bass note.
Play a C major triad in all three inversions at the keyboard and listen carefully to how each sounds: root position sounds stable and conclusive, first inversion lighter and passing, second inversion unstable and demanding resolution. Then write out a four-bar progression using inversions to keep the bass line moving by step rather than jumping.
From your study of chord inversions, you know that a triad contains three notes — root, third, and fifth — and that any of the three can be placed in the bass. What inversion theory adds is a precise vocabulary and a set of functional implications for each position. Root position (5/3 in figured bass, usually just unmarked) places the root in the bass; this is the most stable configuration, where the harmonic identity is unambiguous. First inversion (6/3 or just "6") places the third in the bass; this position feels lighter and more mobile, often used to keep bass lines flowing smoothly without emphasizing the chord change. Second inversion (6/4) places the fifth in the bass and is the most unstable — in tonal music, it almost always requires careful handling.
The reason inversions matter for voice leading is that the bass note creates specific interval relationships with the upper voices. When you move from one chord to the next, choosing the right inversion keeps each voice moving by small steps rather than large leaps. Imagine accompanying a rising melody with block chords: if you always used root position, your bass line would leap around the keyboard. By alternating root position with first inversion, you can construct a bass that moves stepwise — smooth, singable, coherent. This is one of the first practical payoffs of understanding inversion: it gives you the tools to write bass lines that behave melodically rather than mechanically.
The cadential 6/4 deserves special attention because it is the most structurally important use of second inversion in tonal music. This is a I chord in second inversion appearing just before the dominant, typically at a cadence: the bass holds on scale degree 5 while the upper voices move to the 6 and 4 above it, then resolve down by step to the 5 and 3 of the V chord. The 6/4 on scale degree 5 is so unstable that it sounds like a decorated dominant — the upper voices are suspensions that must resolve. This is why the progression feels so conclusive: the cadential 6/4 builds anticipation, and the resolution to V and then I releases it. Recognizing the cadential 6/4 in scores is one of the clearest markers of formal arrival in Classical music.
Figured bass notation, the system of numbers below a bass note, encodes exactly which intervals appear above it. The numbers literally tell you the intervals to play: 6/3 means a sixth and a third above the bass, which is first inversion. 6/4 means a sixth and a fourth, which is second inversion. This notation originated in Baroque music as shorthand for keyboard players improvising accompaniments, but it remains the standard analytical notation. When you see a Roman numeral analysis that reads "I6" or "IV6/4," the superscript is the inversion indicator derived directly from figured bass conventions. Connecting these symbols to the physical act of placing chord tones in the bass closes the loop between notation and sound.
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