Authentic

Authentic (also closed, standard or perfect) cadence: V to I (or V–I). A seventh above the root is often added to create V⁷. The 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." 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.

Perfect authentic cadence: The chords are in root position; that is, the roots of both chords are in the bass, and the tonic (the same pitch as root of the final chord) is in the highest voice of the final chord. A perfect cadence is a progression from V to I in major keys, and V to i in minor keys. This is generally the strongest type of cadence and often found at structurally defining moments. "This strong cadence achieves complete harmonic and melodic closure."

Imperfect authentic cadence (IAC), best divided into three separate categories:

• • 1. Root position IAC: similar to a PAC, but the highest voice is not the tonic ("do" or the root of the tonic chord).

  • 2. Inverted IAC: similar to a PAC, but one or both chords is inverted.

  • 3. Leading tone IAC: the V chord is replaced with the vii^o/subV chord (but the cadence still ends on I).

Evaded cadence: V4

2 to I6

. Because the seventh must fall step wise, it forces the cadence to resolve to the less stable first inversion chord. Usually to achieve this a root position V changes to a V42 right before resolution, thereby "evading" the cadence.

Half cadence

Plagal cadence, Half cadence ("'Imperfect Cadence'" or semicadence): any cadence ending on V, whether preceded by V of V, ii, vi, IV, or I—or any other chord. Because it sounds incomplete or suspended, the half cadence is considered a weak cadence that calls for continuation.

• • Phrygian half-cadence: a half cadence from iv⁶ to V in minor, so named because the semitonal motion in the bass (flat sixth degree to fifth degree) resembles the semitone heard in the ii–I of the ancient (15th century) cadence in the Phrygian mode. Due to its being a survival from modal Renaissance harmony this cadence gives an archaic sound, especially when preceded by v (v-iv6-V). A characteristic gesture in Baroque music, the Phrygian cadence often concluded a slow movement immediately followed by a faster one. With the addition of motion in the upper part to the sixth degree, it becomes the Landini cadence.

  • Lydian cadence: The Lydian half-cadence is similar to the Phrygian-half, involving iv⁶-V in the minor, the difference is that in the Lydian-half, the whole iv⁶ is raised by 1/2 step – in other words, the Phrygian-half begins with the first chord built on scale degree P4 and the Lydian-half is built on the scale degree 4+ (augmented 4th). The Phrygian cadence ends with the movement from iv⁶ → V of bass (3rd of the chord/scale degree 6m) down by semi-tone → bass (the root of the chord/scale degree P5), fifth (scale degree P1) up by whole-tone → fifth (scale degree 2M), and the root (scale degree P4) up by whole-step → octave (scale degree P1/P8); the Lydian half-cadence ends with the movement from a iv⁶ (raised by half step) → V of bass (3rd of the chord/scale degree 6M) down by whole-tone → bass (the root of the chord/scale degree P5), fifth (scale degree 1+) up by half-step → fifth (scale degree 2M), and the root (scale degree 4+) up by half-step → octave (scale degree P1/P8).

  • Plagal cadence: IV to I, also known as the "Amen Cadence" because of its frequent setting to the text "Amen" in hymns. William Caplin disputes the existence of plagal cadences in music of the classical era: "An examination of the classical repertory reveals that such a cadence rarely exists. [...] Inasmuch as the progression IV-I cannot confirm a tonality (it lacks any leading-tone resolution), it cannot articulate formal closure [...]. Rather, this progression is normally part of a tonic prolongation serving a variety of formal functions – not, however a cadential one. Most examples of plagal cadences given in textbooks actually represent a postcadential codetta function: that is, the IV-I progression follows an authentic cadence but does not itself create genuine cadential closure." It may be noticed that the plagal cadence, "leaves open the possibility of interpretation as V-I-V" rather than I-IV-I. The term "minor plagal cadence" is used to refer to the iv-I progression. Sometimes a combination of major and minor plagal cadence is used (IV-iv-I).