Cadence

In Western musical theory, a cadence (from Latin cadentia 'a falling') is the end of a phrase in which the melody or harmony creates a sense of full or partial resolution, especially in music of the 16th century onwards. A harmonic cadence is a progression of two or more chords that concludes a phrase, section, or piece of music. A rhythmic cadence is a characteristic rhythmic pattern that indicates the end of a phrase. A cadence can be labeled "weak" or "strong" depending on the impression of finality it gives.

While cadences are usually classified by specific chord or melodic progressions, the use of such progressions does not necessarily constitute a cadence—there must be a sense of closure, as at the end of a phrase. Harmonic rhythm plays an important part in determining where a cadence occurs. The word "cadence" sometimes slightly shifts its meaning depending on the context; for example, it can be used to refer to the last few notes of a particular phrase, or to just the final chord of that phrase, or to types of chord progressions that are suitable for phrase endings in general.

Cadences are strong indicators of the tonic or central pitch of a passage or piece. The musicologist Edward Lowinsky proposed that the cadence was the "cradle of tonality".

Cadences are divided into four main types, according to their harmonic progression: authentic (typically perfect authentic or imperfect authentic), half, plagal, and deceptive. Typically, phrases end on authentic or half cadences, and the terms plagal and deceptive refer to motion that avoids or follows a phrase-ending cadence. Each cadence can be described using the Roman numeral system of naming chords.

An authentic cadence is a cadence from the dominant chord (V) to the root chord (I). During the dominant chord, a seventh above the dominant may be added to create a dominant seventh chord (V⁷); the dominant chord may also be preceded by a cadential ⁶
₄ chord. The Harvard Concise Dictionary of Music and Musicians says, "This cadence is a microcosm of the tonal system, and is the most direct means of establishing a pitch as tonic. It is virtually obligatory as the final structural cadence of a tonal work." Authentic cadences are generally classified as either perfect or imperfect. The phrase perfect cadence is sometimes used as a synonym for authentic cadence but can also have a more precise meaning depending on the chord voicing.

In a perfect authentic cadence (PAC), the chords are in root position – that is, the roots of both chords are in the bass – and the tonic is in the highest voice of the final chord. This is generally considered the strongest type of cadence and often found at structurally defining moments. Music theorist William Caplin writes that the perfect authentic cadence "achieves complete harmonic and melodic closure."

There are three types of imperfect authentic cadences (IAC):

An evaded cadence (a subtype of the inverted IAC) moves from a dominant seventh third inversion chord (V⁴
₂) to a first inversion tonic chord (I⁶
). Because the seventh of the dominant chord must fall stepwise to the third of the tonic chord, it forces the cadence to resolve to the less stable first inversion chord. To achieve this, a root position V usually changes to a V⁴
₂ right before resolution, thereby "evading" the root-position I chord that would usually follow a root-position V. (See also inverted cadence below.)