Six-three chord (Sextakkord)
First inversion: the third lies in the bass. Sounds lighter and more floating than the root position.
What it means
The Sextakkord is the first inversion of a triad: the third lies in the bass, above it stand the fifth and the root at the distance of a third and a sixth from the bass. The characteristic sixth gives it its name; in figured-bass notation it is designated 6.
Musical use
Tonally the Sextakkord seems lighter and less settled than the root position. It does not rest but presses onward, and is therefore hardly suited as a closing sonority, but well suited to the course of a movement. Its most important task is bass leading: with six-three chords a bass can be led stepwise where root positions would make it leap, and the sonorities connect more smoothly.
In four-part writing the rule holds not to double the third in the bass, because it would otherwise stand out excessively — especially if it is the leading tone. Instead the root or the fifth is doubled.
Historically the Sextakkord has a special position. In the fifteenth-century faux-bourdon the whole texture rests on chains of parallel six-three chords. And several fixed harmonic formations carry its name, although they are special cases: the Neapolitan sixth chord is a major triad on the lowered second degree in first inversion, the augmented sixth chord an altered formation with an augmented sixth above the bass.
It is frequent in chains of six-three chords, for instance in fauxbourdon, where parallel-led six-three chords produce a soft sound. In function theory the third in the bass stands as a small 3 under the symbol. In four-part writing the third is usually not doubled, especially with major six-three chords, but rather the root or the fifth. The Sextakkord is the most common inversion, because it makes the bass mobile without greatly reducing stability.
Performance practice
Give a Sextakkord less weight than a root position — it leads onward and should not become heavy. Watch the bass line that arises through six-three chords, and phrase it as a line. And avoid, in your own writing, doubling the bass note, especially when it is the leading tone.