AP Music Theory Unit 4 Notes: Function, Cadence, and Phrase in Tonal Harmony

Chord function

The idea that chords in tonal music play characteristic roles (e.g., “home,” “away,” “tension/resolution”) based on how they behave in context.

Tonic function

A harmonic role that conveys stability and arrival; often appears at the beginning of phrases to establish the key and at cadences to confirm it.

Dominant function

A harmonic role that creates strong tension and a clear expectation to resolve to tonic, driven by tendency tones (especially scale degrees 7 and 4).

Subdominant function (Predominant function)

A harmonic role that prepares the dominant; less stable than tonic and commonly moves into dominant harmony to set up a cadence.

Tendency tones

Notes with strong directional pull that make a particular resolution feel expected (central to dominant function).

Leading tone (scale degree 7)

Scale degree 7 in major/minor that strongly wants to rise to scale degree 1; crucial for strengthening dominant function (especially in minor when raised).

Scale degree 4 tendency in V7

In a V7 chord, scale degree 4 often acts as the chordal seventh and commonly resolves downward to scale degree 3.

Functional flow (typical progression)

A common-practice pattern of harmonic motion: Tonic → Predominant → Dominant → Tonic.

Tonic-function diatonic triads (major)

In major keys, the most common tonic-function triads are I, vi, and iii, used to establish/confirm or prolong “home.”

Predominant-function diatonic triads (major)

In major keys, the most common predominant (subdominant) triads are ii and IV, typically leading into dominant harmony.

Dominant-function diatonic triads (major)

In major keys, the most common dominant-function triads are V and vii°, creating the strongest drive to resolve to I.

Raised scale degree 7 in minor

A common minor-key practice that turns scale degree 7 into a leading tone, strengthening dominant function (so V and vii° are often used instead of v and VII).

Prolongation

Extending a harmonic function over time (often tonic) using voice-leading motion, inversions, or substitutions rather than immediately moving to a cadence.

Neighbor/passing motion (as prolongation)

Stepwise melodic motions in individual voices that add movement while the underlying harmony/function remains the same (commonly used to prolong tonic).

Inversion (and function)

A chord voicing with a non-root bass; inversions change spacing/bass but do not change the chord’s basic harmonic function (e.g., V6 is still dominant).

Functional substitution

Using a different chord that shares tones and serves the same function (e.g., vi often substitutes for I as a tonic-function chord in major).

Cadence

A harmonic “punctuation mark” that signals the end of a musical idea or a resting point, identified mainly by the final harmonies and their voicing.

Authentic cadence (AC)

A dominant-to-tonic ending: V (or V7) resolving to I (or i in minor), producing the most goal-directed tonal closure.

Perfect Authentic Cadence (PAC)

The strongest V–I cadence: ends V→I (or V7→I), both chords in root position, with the soprano ending on scale degree 1.

Imperfect Authentic Cadence (IAC)

A V–I cadence that is less final than a PAC because a strength condition is missing (e.g., inverted chord(s) or soprano ends on scale degree 3 or 5).

Half cadence (HC)

A cadence that ends on V (often root position), creating an unfinished “comma” feeling regardless of what chord precedes it.

Plagal cadence (PC)

A cadence with IV→I (or iv→i), often called the “Amen” sound and generally less forceful than an authentic cadence.

Deceptive cadence (DC)

A cadence-like motion where V resolves unexpectedly to a different chord—most commonly V→vi in major (or V→VI in minor)—to avoid full closure and extend the phrase.

Phrase

A musical unit that feels like a complete thought, typically shaped by motion toward a cadence; often (but not always) about 4 measures in common-practice styles.

Period

A two-phrase structure (antecedent then consequent) featuring a “question–answer” relationship: the first phrase ends weaker (often HC) and the second ends stronger (often AC).