What is the interval designation for a 1st inversion seventh chord?

The interval designation for a 1st inversion seventh chord is expressed as 6/5. This designation indicates the relationship between the bass note and the other notes in the chord. In a 1st inversion seventh chord, the third of the chord is in the bass position, resulting in the chord being built above that bass note.

To understand the designation, let's break it down: in a seventh chord, the root is typically a stack of four notes (the root, third, fifth, and seventh). When the chord is in 1st inversion, the structure is such that the root is no longer the lowest note. Instead, the lowest note is the third. This means that from the bass note (the third), the interval to the next note (the fifth) is a sixth, and the interval from the third to the seventh above it is a fifth. Therefore, the chord's inversion reflects this stacking of intervals as 6/5.

This is relevant and informative for those studying music theory, as understanding how inversions work will aid in composing and analyzing music effectively. The other options reflect different types of chord degrees or inversions related to other contexts in harmony, but they do not apply specifically to the 1st inversion