Inversions, and why the bass decides the weight
The same three notes with a different note underneath are still the same chord — but they do not weigh the same, and that is why a sequence of chords sounds like music instead of blocks.
A chord is a set of notes, not an order. C, E and G are C major with the C underneath and with the G underneath. What changes when the lowest note changes is not the chord's identity: it is its weight, and the path the bass takes to the next chord.
Three positions
A triad has three notes, so three candidates for the bass. Each one gives a position its name:
- Root position — the root underneath: C, E, G.
- First inversion — the third underneath: E, G, C.
- Second inversion — the fifth underneath: G, C, E.
Play the three in a row. It is the same chord, and it does not sound the same: root position is the firmest, first inversion is lighter, second inversion hangs in the air, asking to go somewhere.
The slash in the chart
A chart writes an inversion with a slash: before it, the chord; after it, the note that goes in the bass.
is C major with E in the bass, first inversion. is C major with G in the bass, second inversion. The letter after the slash is not a second chord and changes nothing about the quality: it only tells the bass player, or the left hand, which note to play underneath.
The rule holds for any chord. is A minor in first inversion; is a four-note chord with the third in the bass, and the fourth note, the seventh, could go underneath too: , third inversion, which exists only in four-note chords.
What it is for
The practical answer is in the bass. Play C major, F major and G major, all in root position: the bass leaps a fourth up, then a second, and each chord arrives as a block.
Now swap the second chord for the second inversion of F and the third for the first inversion of G:
The bass stays on C, falls a semitone to B, comes back to C. The chords are the same; the passage has become a line. That is the commonest use of inversion: making the bass walk by step instead of leaping.
In four voices, with the analysis under it:
The descending bass
The classic case is the bass walking down the scale while the chords stay diatonic. From C to A, step by step:
Every slash chord is there because of the bass: G major in first inversion puts B under the chord, C major in second inversion puts G, and the bass line descends without skipping a note. Without the inversions, the same sequence of degrees would sound like a staircase of blocks. The same descent in four voices, with the analysis under it; C over G, the fourth chord, is the passing second inversion:
Inversion is not voicing
Two things get confused here. Inversion says which note is in the bass, and only that. Voicing says how the other notes are spread above: close, open, doubled, with the fifth omitted. is still first inversion with the G an octave higher or with two Cs; inversion is a property of the bass, voicing is a choice about the rest.
What to take from here
To invert is to choose the bass. The chord does not change its name, it changes its weight: root position settles, first inversion softens, second inversion pushes. The chart writes the choice with a slash, and the reason for nearly every inversion is a bass line that walks instead of leaping. Out of this come the voice leading and the descending bass that appear in half the songs you know.
