Third-fourth chord
The second inversion of a seventh chord: the fifth lies in the bass.
What it means
The third-fourth chord (Terzquartakkord) is the second inversion of a seventh chord: the fifth lies in the bass, and above it stand the seventh, the root, and the third. The characteristic intervals above the bass are the third and the fourth; in figured bass it is marked 4/3.
Musical use
As an inversion of the dominant seventh chord, the third-fourth chord has the fifth of the dominant in the bass. This can move both upward and downward, which is why the sound is especially well suited to passing motion. Typical is its position between two placements of the tonic: the bass moves from the root of the tonic, via the fifth of the dominant, up to the third of the tonic, or downward in the reverse direction, with the third-fourth chord standing on the middle note. In this role it resembles the passing six-four chord but sounds more colourful, because it contains a seventh.
The resolution follows the usual rules: the leading tone rises to the root, the seventh falls to the third of the tonic. If the bass leads upward, the seventh may exceptionally rise along with it, to avoid voice crossings or parallels — one of the few permitted deviations from the rule of the downward-resolved seventh.
In four-part writing, the third-fourth chord as a rule contains all four notes of the seventh chord.
Compared with the other inversions it seems the least weighty: it is a connecting sonority, not a goal sonority.
In figured bass, the third-fourth chord stands as 4/3. With the dominant seventh chord, the fifth lies in the bass, and the chord mostly leads to the tonic in root position or to the six-three chord; the bass moves stepwise in the process. In function theory the inversion is shown with a small 5 under the symbol. Because the bass here is neither the root nor a dissonant note, the chord seems comparatively balanced and is well suited as a passing chord.
Performance practice
Treat the third-fourth chord as a passing element — light and connecting, without emphasis. Follow the bass line it stands in; that is usually the real context. And check the leading of the seventh: downward as a rule, upward only when the bass demands it.