A cadence is a musical event that ends a phrase. Cadences in Western common-practice music are primarily characterized by their harmonic properties.

There are two categories of cadences differentiated by their arrival harmonies. An arrival harmony is the chord on which the cadence occurs.

Half cadence (HC) - arrives on a root-position V or V7 chord from any other chord
- The V(7) chord may be embellished by a cadential 6/4. In such a case, the HC label should be placed above the cadential 6/4 chord. (Again, this is because the cadential 6/4 is essentially a V chord with "decorations.")
Authentic cadence (AC) - arrives on a root-position I (major) or i (minor) chord from a root-position V or V7
- The V(7) chord may be embellished by a cadential 6/4.

As explained above, root-position chords are necessary to achieve a cadence. Inverting the V chord in a half cadence would nullify the cadence, as would inverting V or I in an authentic cadence.

Some instructors and institutions teach the existence of "inverted IACs." To align with Texas State's undergraduate textbook, we will not observe these here.

The diagrams below show two example progressions with cadences at their ends. Note that when V, V7, or I are inverted, no cadence occurs.

Cadence								HC
Chord	I	V42	I6	V43	I	vi	ii6	V

Cadence								AC
Chord	i	i6	V65	i	VI	iv	V7	i

Authentic cadences can further be distinguished by the melody note on which they arrive:

Perfect authentic cadence (PAC) - melody arrives on scale degree 1
Imperfect authentic cadence (IAC) - melody arrives on scale degree 3 or 5

The diagrams below show examples of progressions with authentic cadences:

Cadence				PAC
Scale degree in melody	3	2	2	1
Chord	i	ii°6	V7	i

Cadence				IAC
Scale degree in melody	3	4	2	3
Chord	I	IV	V	I

Other musical features may strengthen the interpretation of a cadence:

Use of predominant chords and/or cadential 6/4 near the cadence
Confluence between arrival harmony and the bottom end of a descending melody
Long rhythmic duration on the arrival harmony/melodic note

In a 2020 paper,¹ Jarvis and Peterson outlined the factors below for identifying cadences. You may find them useful.

Process completion: A process starts, is worked out, and concludes.
Boundary detection: Identification of edges of a phrase—the end of one unit and the beginning of another (often via contrast and/or repetition)
Confirmation: Created by, for example, a new beginning or the absence of more music

¹Jarvis, Brian and John Peterson. 2020. "Don’t Count Your Cadences Before They Hatch: Advocating for Discussions of Closure in Pedagogical Contexts." Paper presented at Texas Society for Music Theory 2020 Annual Meeting.