cadential six-four
A second-inversion tonic chord used at cadences, functioning as a decoration of the dominant rather than a true tonic
In Depth
The cadential 6/4 (I6/4) appears over the dominant bass note, with the sixth and fourth above it resolving down by step to become the fifth and third of the dominant chord. Despite being spelled as a tonic triad, it functions as an embellishment of V. Many theorists label it V6/4 to reflect this function. The cadential 6/4 is one of the most common harmonic events in Classical music, appearing at virtually every authentic cadence in Mozart, Haydn, and Beethoven.
The labelling of the cadential 6/4 — as I6/4 or V6/4 — is one of the most contentious debates in music theory pedagogy, with strong advocates on both sides.