AP Music Theory Unit 4 ReviewChord Function, Cadence, and Phrase

AP Music Theory Unit 4 is where the course shifts from naming chords to using them. The big idea is functional harmony, the system from roughly 1650 to 1900 where every chord plays a role (tonic, predominant, or dominant) in a progression that pulls toward a central pitch. You learn the 18th-century voice leading rules that connect those chords smoothly, and you learn to hear and label the cadences that punctuate phrases. Almost everything you write, analyze, and dictate for the rest of the course runs on the rules in this unit.

What this unit covers

Functional harmony and the tonal system

• Music is tonal when every pitch relates to one central pitch, the tonic, in a fixed hierarchy. This is the organizing logic of common practice music (roughly 1650 to 1900), and it also shows up in pop, folk, and film music.
• Chords sort into three functional families. Tonic (I) is home and stability. Dominant (V and vii°) creates tension that pulls back to tonic, mostly because it contains the leading tone. Predominant (ii and IV) sets up the dominant.
• The basic circuit is tonic, then predominant, then dominant, then tonic. Think of it like a sentence: subject, build-up, tension, resolution. Progressions that skip backward (like V going to IV) break the style.
• Roman numerals label each chord by scale degree, with Arabic numerals (figures) added to show inversion. An accurate analysis has to account for every note in the score.

Cadences and phrases

• A phrase is a complete musical utterance that ends with a cadence. Four-measure and eight-measure phrases are the norm, but other lengths happen. Cadences work like punctuation, regulating the flow of the music.
• Conclusive cadences end with finality. A perfect authentic cadence (PAC) is V (or V7) to I with both chords in root position and the soprano ending on the tonic. A plagal cadence (IV to I) is the softer "Amen" ending.
• Inconclusive cadences leave the music hanging. A half cadence (HC) stops on V, like a comma. An imperfect authentic cadence (IAC) is V to I but weakened (soprano not on tonic, or an inversion involved). A deceptive cadence resolves V to vi instead of I, the musical fake-out.
• You identify cadences both in notated scores and by ear in performed music, so practice both modes.

Soprano-bass counterpoint

• The outer voices (soprano and bass) are the skeleton of tonal music. Given a soprano line, you compose a bass line that implies a sensible harmonic progression using tonic, supertonic, subdominant, and dominant triads.
• A good bass line balances steps and leaps and balances upward and downward motion. The bass leaps more than upper voices. Allowed leaps include thirds, perfect fourths and fifths, sixths, octaves, and a properly resolved descending diminished fifth. After an octave leap, change direction.
• Rhythmically, chorale bass lines run mostly in quarter notes, with half notes and eighth notes mixed in. A bass line in all half notes would be out of style.
• Every phrase ending in the bass must imply an appropriate cadence, and the implied chords must make harmonic sense with the soprano notes above them.

SATB voice leading rules

• Four-voice texture uses soprano, alto, tenor, and bass (SATB). Figured bass and chorale harmonization exercises live in this texture.
• Doubling rule of thumb: double the root of a triad whenever voice leading allows. Spell every chord correctly, including any needed accidentals.
• Tendency tones resolve by stylistic precedent. The leading tone wants to rise to tonic, and a chordal seventh resolves down by step.
• Motion between outer voices (contrary, similar, parallel, oblique) should vary. Never write more than three consecutive thirds or three consecutive sixths between voices. Avoid parallel perfect fifths and octaves, and handle the diminished fifth so it does not rise to a perfect fifth (unequal fifths).
• First inversion triads follow all the same conventions and give the bass line melodic flexibility.

Seventh chords and their inversions

• The chordal seventh is the most regulated note in part writing. Approach it by common tone or by step (ascending leap is a backup option, descending leap of a third is rare), and always resolve it down by step.
• Seventh chords in inversion (6/5, 4/3, 4/2 figures) usually connect chords in longer progressions and let the bass move by step. Voice leading into and out of them stays smooth, with minimal leaps.
• Leading-tone seventh chords (vii°7 fully diminished and viiø7 half diminished) can substitute for V or V7 as dominant-function chords, and they follow the same tendency-tone logic.

Unit 4, Chord Function, Cadence, and Phrase at a glance

Why Unit 4, Chord Function, Cadence, and Phrase matters in AP Music

This unit is the engine room of AP Music Theory. Units 1 through 3 gave you the vocabulary (scales, keys, intervals, triads, seventh chords), and Unit 4 is the grammar that turns that vocabulary into actual music. Every harmony skill on the exam, written or aural, assumes you have internalized these rules.

• Functional harmony is the course's central model for how tonal music works. Tonic, predominant, and dominant labels are how you explain why a progression sounds finished or unfinished.
• The 18th-century voice leading conventions here are the grading rubric for the part-writing free-response questions. Parallel fifths and unresolved sevenths cost points directly.
• Cadence and phrase identification connects written theory to listening. Hearing a half cadence versus a PAC is one of the most testable aural skills in the course.

How this unit connects across the course

• Key signatures, scale degrees, and meter (Unit 1) and minor keys (Unit 2) tell you which triads are major, minor, or diminished, which is the basis for every Roman numeral you write here.
• Triads and seventh chords with inversion symbols (Unit 3) are the raw material. Unit 4 takes those isolated chords and strings them into progressions with rules for how voices move between them.
• Predominant expansion (Unit 5) builds directly on the tonic-predominant-dominant circuit from this unit, adding chords like ii6 and IV in richer progressions plus 6/4 chord types.
• Embellishments and non-chord tones (Unit 6) decorate the voice-leading framework you build here, and secondary function (Unit 7) applies your V7 and vii°7 resolution habits to chords that tonicize other scale degrees. Phrase and cadence skills pay off again in form analysis, including periods (Unit 8).

Key notation and chord types

• Roman numerals (I, ii, IV, V, vi, vii°): label a chord by scale degree, uppercase for major, lowercase for minor, ° for diminished. The core of all harmonic analysis.
• Figured bass / Arabic numerals: numbers below a bass note showing intervals above it. For triads, 6 means first inversion and 6/4 means second inversion.
• Seventh chord figures (7, 6/5, 4/3, 4/2): root position, first, second, and third inversion of a seventh chord. In a 4/2 chord, the seventh is in the bass and must resolve down by step.
• V7 (dominant seventh): the strongest dominant-function chord. Its leading tone rises and its seventh falls, both by step, into the tonic chord.
• vii°7 and viiø7 (leading-tone sevenths): fully diminished and half diminished sevenths on the leading tone. Both can substitute for V or V7 as dominant function.
• Cadence labels (PAC, IAC, HC, DC, plagal): shorthand for cadence types. Get fluent at writing and recognizing these abbreviations fast.
• SATB voicing: four-part texture with soprano, alto, tenor, bass. Watch spacing (no more than an octave between adjacent upper voices) and avoid voice crossing.
• Tendency tone arrows: many teachers mark the leading tone resolving up and the chordal seventh resolving down. Train yourself to spot both instantly in any voicing.

Unit 4, Chord Function, Cadence, and Phrase on the AP exam

This unit feeds both halves of the exam, the aural and the written. On the multiple-choice side, you analyze scores (label Roman numerals, inversions, and cadences), detect voice leading errors in short SATB excerpts, and answer listening questions that ask you to identify cadence types and harmonic function in performed music.

On the free-response side, this unit is the foundation for the part-writing tasks. One task gives you a figured bass to realize in four voices, another gives you a Roman numeral progression to voice in SATB, and a third asks you to compose a bass line under a given soprano melody, implying logical harmony with appropriate cadences at phrase endings. Harmonic dictation also lives here. You hear a progression and notate the soprano and bass lines plus Roman numerals with inversion figures. In all of these, the rules from this unit (doubling, spacing, parallel motion, tendency tone resolution, seventh resolution) are exactly what gets scored. A technically "correct" chord with parallel fifths loses points, so build the habit of checking outer voices and tendency tones every time you write.

Essential questions

• Why do certain chord progressions sound inevitable while others sound wrong, and what does "function" mean in tonal music?
• How do cadences act as musical punctuation, and how do they define where phrases begin and end?
• Why did 18th-century composers follow strict voice leading conventions, and what musical effect do those rules produce?
• How do the outer voices (soprano and bass) carry enough information to imply an entire harmonic progression?

Key terms to know

• Voice leading: how individual voices move from chord to chord, aiming for smooth, independent lines.
• Functional harmony: the system where chords act as tonic, predominant, or dominant within a key.
• Tonic function: the role of the I chord as home base, the point of stability and resolution.
• Dominant function: the tension-creating role of V and vii°, pulling strongly toward tonic.
• Predominant function: the role of ii and IV chords that set up and lead into the dominant.
• Cadence: a point of relative repose that ends a harmonic progression or phrase.
• Perfect authentic cadence (PAC): V to I in root position with the soprano ending on the tonic, the strongest possible ending.
• Half cadence (HC): a phrase ending on V, leaving the music sounding unfinished.
• Deceptive cadence: V resolving to vi instead of the expected I.
• Tendency tone: a note with a strong pull, like the leading tone (up to tonic) or the chordal seventh (down by step).
• Doubling: assigning one chord member to two voices in four-part writing, usually the root.
• Phrase: a complete musical utterance, often four or eight measures, ending with a cadence.
• Figured bass: a bass line with numbers indicating the intervals (and therefore chords and inversions) to build above it.
• Parallel fifths and octaves: forbidden motion where two voices move in the same direction keeping a perfect fifth or octave between them.

Common mix-ups

• PAC vs. IAC: both are V to I, but a PAC requires root position in both chords AND the tonic in the soprano. Miss either condition and it drops to an IAC. Check the soprano note before you label.
• Deceptive cadence vs. half cadence: a half cadence stops ON V; a deceptive cadence moves THROUGH V to vi. One pauses on tension, the other resolves it somewhere unexpected.
• Resolving vs. approaching the seventh: the chordal seventh always resolves down by step, but it can be approached several ways (common tone or step preferred). Don't confuse the strict resolution rule with the more flexible approach options.
• vii° is dominant, not its own function: leading-tone chords substitute for V or V7. Treat vii°7 as dominant function, not as a random diminished chord.