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.
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.
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.