Cadences in Music: Perfect, Plagal, Deceptive, and Half Cadences

Cadences are harmonic punctuation marks that define phrase structure across every major Western musical tradition, from 16th-century counterpoint to contemporary film scoring. Understanding the four principal cadence types — perfect authentic, plagal, deceptive, and half — is foundational to analyzing how composers create tension, release, and formal architecture. This page classifies each cadence by its chord motion, voice-leading requirements, and expressive function, drawing on the theoretical frameworks codified in standard conservatory pedagogy. A broader orientation to structural concepts appears in Key Dimensions and Scopes of Music Theory.

Definition and Scope

A cadence is a harmonic formula that signals the end of a musical phrase, section, or complete work. The term refers specifically to the closing chord progression — typically the final 2 to 4 chords of a phrase — rather than to any single chord in isolation. Cadences operate at multiple formal scales: a half cadence might close a 4-bar antecedent phrase, while a perfect authentic cadence closes an entire movement.

Western tonal music theory, as systematized by theorists including Heinrich Schenker and as codified in the pedagogical tradition represented by texts such as Walter Piston's Harmony (first published 1941, Harvard University Press), recognizes four primary cadence categories:

1. Perfect Authentic Cadence (PAC) — dominant to tonic (V→I), with both chords in root position and the tonic scale degree in the soprano voice on the final chord.
2. Imperfect Authentic Cadence (IAC) — dominant to tonic motion, but failing at least one PAC requirement (inverted chord, non-tonic soprano, or use of vii° instead of V).
3. Plagal Cadence — subdominant to tonic (IV→I), associated with liturgical and folk-influenced music.
4. Half Cadence (HC) — any progression ending on the dominant (V), producing an inconclusive, questioning effect.
5. Deceptive Cadence (DC) — the dominant resolves to an unexpected chord, most commonly vi instead of I, frustrating the expectation of closure.

The Music Theory Frequently Asked Questions resource addresses common confusions between IAC and PAC classification.

How It Works

Each cadence type produces its effect through the interaction of two forces: bass motion and melodic expectation. The dominant chord (built on scale degree 5) contains the leading tone (scale degree 7), which carries a strong voice-leading pull upward by a half step to the tonic. How that tension resolves — or fails to resolve — determines cadence type.

Perfect Authentic Cadence: The V chord in root position moves to I in root position. The leading tone resolves up to the tonic. The soprano arrives on scale degree 1 (do). This configuration produces the strongest possible sense of closure and is the standard ending for Classical-period movements. In a C-major context, this means a G major chord (G–B–D) resolving to C major (C–E–G), with B in an upper voice stepping up to C.

Half Cadence: The phrase ends on V without resolving. The leading tone is left unresolved, creating an expectation that demands continuation. Composers use the HC to close antecedent phrases in a period structure — the musical equivalent of a comma rather than a period. The Phrygian Half Cadence is a specific variant common in Baroque music, in which iv6 (first-inversion minor subdominant) moves to V.

Plagal Cadence: The subdominant (IV) moves to tonic (I). Because IV does not contain the leading tone, the resolution is softer and less directional than an authentic cadence. The plagal cadence appears in sacred music with notable frequency — the "Amen" cadence in hymns is almost universally plagal. In a C-major context: F major (F–A–C) resolving to C major (C–E–G).

Deceptive Cadence: The dominant prepares an expected authentic resolution but lands on vi (the submediant) instead. In C major, G major resolves to A minor. Because vi shares two pitch classes with I (in C major, both chords contain E and G), the resolution is partially satisfying but harmonically surprising. Composers use this device to extend phrases, avoid premature closure, or create expressive intensity at textual climaxes.

Common Scenarios

Cadence choices map predictably onto formal contexts across the common-practice period (roughly 1600–1900):

• Sonata form expositions typically close the primary theme area with a PAC in the home key before transitioning to the secondary key area.
• Period structures (common in Classical-period minuets and theme statements) pair an antecedent phrase ending on a HC with a consequent phrase ending on a PAC — a question-and-answer architecture.
• Baroque chorales, the primary pedagogical material for cadence study in institutions following the College Music Society curriculum guidelines, exhibit all four cadence types within a single 4-voice chorale, making them the standard analytical object for cadence classification exercises.
• Gospel and blues harmony extend plagal cadential motion into characteristic IV–I oscillation patterns that persist across entire sections rather than functioning as single phrase endings.
• Film scores exploit deceptive cadences at dramatic pivot points, where an anticipated resolution is withheld to sustain narrative tension.

Decision Boundaries

Correctly identifying a cadence requires applying criteria in a specific order. The following 4-step protocol reflects standard analytical practice:

1. Identify the final chord of the phrase. If it is not I or V, the cadence may be deceptive (ends on vi), plagal-extended, or modal.
2. Identify the penultimate chord. V or vii° before I signals an authentic or deceptive cadence. IV before I signals plagal. Any chord before V signals a half cadence.
3. Check bass position. Root-position V moving to root-position I is required for PAC status. Any inversion disqualifies the PAC classification, producing an IAC instead.
4. Check soprano voice. Even with root-position bass, a soprano arriving on scale degree 3 or 5 (rather than 1) on the tonic chord downgrades a potential PAC to an IAC.

The PAC vs. IAC boundary is the most frequently misapplied distinction in undergraduate analysis. A progression that satisfies bass-position requirements but places scale degree 3 in the soprano — a common occurrence in 4-voice chorale writing when the alto doubles the third — cannot be classified as perfect. This precision matters because formal analysis in Key Dimensions and Scopes of Music Theory depends on accurate cadence identification to determine phrase boundaries and sectional hierarchy.

The deceptive cadence presents its own classification challenge: the substitute chord is almost always vi, but theorists including those cited in the Oxford Music Online reference platform acknowledge that other substitutions (IV, VI in minor, or ♭VII) can fulfill the deceptive function when context establishes a frustrated V→I expectation. The deceptive label applies to the harmonic function, not to a fixed chord pair.

Half cadences that arrive via iv6–V in minor keys carry the specific Phrygian label because the bass motion (down a half step from the fourth scale degree to the fifth) replicates the characteristic descending semitone of the Phrygian mode. This subtype appears with particular density in J.S. Bach's harmonizations, making Bach chorales the primary analytical source for encountering the Phrygian HC in a pedagogically structured context. Additional foundational concepts that intersect with cadence analysis, including scale systems and harmonic function, are addressed in the Music Theory Frequently Asked Questions section.