AP Music Theory Harmony and Voice Leading Review: Core Principles
The Goals of Good Part Writing
The fundamental objective of voice leading is to maintain the independence of four distinct musical lines while creating a unified harmonic structure. In the context of the AP exam, this is modeled after the 18th-century chorale style. Independent lines are achieved by avoiding simultaneous movement in the same direction at the same interval, which would cause the voices to lose their unique identities. The scoring rubric for the exam prioritizes smooth, stepwise motion over large, disjunct leaps. A primary goal is to ensure that each chord is complete, containing the root, third, and fifth, while managing the horizontal flow of the melody. This involves a delicate balance: the Soprano must be tuneful and the Bass must provide a strong harmonic foundation, while the inner voices (Alto and Tenor) provide the necessary harmonic filler with minimal movement. Understanding the voice leading errors to avoid, such as overlapping or crossing parts, is critical for maintaining this independence.
Standard Four-Part Chorale Texture and Ranges
To write effectively for a four-part ensemble, a candidate must respect the physical limitations of the human voice. The AP exam strictly enforces specific vocal ranges for each part. The Soprano typically spans from C4 to G5, the Alto from G3 to C5, the Tenor from C3 to G4, and the Bass from F2 to C4. Exceeding these ranges, even by a semitone, can result in a deduction of points. Furthermore, the vertical spacing between voices is governed by the Rule of the Octave: the distance between Soprano and Alto, and between Alto and Tenor, should not exceed an octave. However, the distance between the Tenor and Bass is more flexible and can exceed an octave to accommodate the harmonic depth of the lower register. Maintaining this texture ensures that the chords sound balanced and that the individual lines remain distinct within the overall frequency spectrum of the chorale.
Chord Construction and Inversion Fundamentals
Spacing and Doubling Rules for Root Position and Inversions
When constructing chords in root position, the general rule is to double the root of the triad. This reinforces the harmonic foundation and provides the most stable sound. However, as chords move into inversions, doubling rules become more nuanced. In a first-inversion major triad, doubling the soprano or the bass (the third of the chord) is often acceptable, but doubling the leading tone is strictly forbidden. The leading tone is a tendency tone that must resolve to the tonic; doubling it would inevitably lead to parallel octaves when both voices resolve. For diminished triads, which almost always appear in first inversion (vii°6 or ii°6), the third of the chord (the bass note) is the preferred note to double. In second-inversion chords, the bass (the fifth of the triad) must be doubled to stabilize the inherently dissonant nature of the 6/4 position. Mastery of these doubling conventions is a prerequisite for high marks in AP Music Theory FRQ 1 and 2.
When to Use First and Second Inversion Chords
Inversions are not used randomly; they serve specific functional purposes in a progression. First-inversion chords (indicated by the figure 6) are primarily used to create a more melodic and stepwise bass line, reducing the number of clunky leaps in the lowest voice. They also provide a lighter harmonic texture compared to the weight of a root-position chord. Second-inversion chords (6/4) are much more restricted and are generally only used in three specific contexts: the Cadential 6/4, which precedes a V chord at a cadence; the Passing 6/4, which connects two versions of the same chord (like I - V6/4 - I6); and the Pedal 6/4 (or neighboring 6/4), where the bass remains stationary while the upper voices move. Using a 6/4 chord outside of these specific idioms is a common error that signals a lack of theoretical depth to the graders.
The Essential Rules of Voice Motion
Conjunct Motion vs. Leaps: Guidelines for Each Voice
Smooth voice leading relies heavily on conjunct (stepwise) motion. The inner voices, Alto and Tenor, should move as little as possible, often staying on a common tone between chords or moving by a second. The Soprano line should be primarily stepwise but can include small leaps (thirds or fourths) to create a pleasing melodic contour. The Bass line is the most prone to disjunct motion, frequently leaping by fourths and fifths to define the harmonic progression. However, certain leaps are universally avoided in all voices, such as augmented intervals (like the Augmented 2nd in minor keys) and leaps larger than a sixth, with the exception of the octave. When a leap does occur, it should ideally be followed by motion in the opposite direction to "recover" the leap and maintain the balance of the melodic line.
The Forbidden Parallels: Fifths, Octaves, and Unisons
The most significant errors in any chorale harmonization are parallel perfect fifths and parallel perfect octaves. These occur when two voices that are a perfect fifth or octave apart move to a new pitch while maintaining that same interval. This motion destroys the independence of the voices, making them sound like a single, thickened line. Additionally, students must watch for direct fifths or octaves (also known as hidden fifths), which occur when the outer voices (Soprano and Bass) move in the same direction into a perfect interval, and the Soprano leaps into that interval. To avoid these, students should utilize contrary motion—moving voices in opposite directions—whenever possible. Even a single instance of parallel fifths can significantly lower a score on the FRQs, as it violates the core principle of Western common-practice harmony.
Resolving Tendency Tones: The Leading Tone and Chordal Sevenths
Certain notes within a scale or chord have a strong "desire" to move to a specific pitch. The most prominent is the leading tone (scale degree 7), which must resolve upward to the tonic (scale degree 1) when it is in an outer voice or part of a V-I cadence. Failure to resolve the leading tone is a frequent point of deduction. Similarly, the chordal seventh in any seventh chord (such as the 7 in a V7) must resolve downward by step. For example, in a V7 to I progression, the 4th scale degree (the seventh of the V7 chord) must move down to the 3rd scale degree. If the seventh is not resolved correctly, the harmonic tension is left "hanging," which contradicts the functional logic of the style. These rules are non-negotiable in the AP curriculum and form the basis of the "check-list" approach many successful students use during the exam.
Harmonizing a Melody and Creating a Bass Line
Choosing Chord Progressions Based on Melodic Notes
In FRQ 1, where a melody is provided, the first step is to identify the possible chords that could support each note. A note like the tonic (scale degree 1) could be harmonized with a I chord, a IV chord, or even a vi chord. The choice depends on the surrounding context and the goal of creating a logical harmonic flow. Students should follow the standard harmonic progression chart: Tonic moves to anything, Predominant (ii or IV) moves to Dominant (V or vii°), and Dominant moves to Tonic. Avoid "retrogression," such as moving from V to ii, which sounds stylistically incorrect. By mapping out the functional "path" of the progression first, students can ensure that their harmonization feels purposeful and leads clearly toward the cadence.
Creating a Strong, Logical Bass Line
The bass line is the engine of the harmony. When harmonizing a melody, the bass should ideally move in contrary motion to the soprano to provide balance. A strong bass line utilizes a mix of root-position chords for stability and first-inversion chords for fluidity. For instance, using a I - V6 - I progression creates a more elegant stepwise bass (1-7-1) than the more static I - V - I. The bass must also clearly articulate the rhythm of the harmony, usually changing notes on every beat or every other beat in a 4/4 meter. It is important to ensure the bass does not become too "jumpy"; while leaps of 4ths and 5ths are standard, consecutive leaps in the same direction should be avoided as they can inadvertently outline a dissonant interval or lead the voice out of its comfortable range.
Cadence Placement for Phrase Structure
Cadences are the punctuation marks of music, and their correct placement is vital for a successful chorale. The most common cadences required on the AP exam are the Authentic Cadence (V to I), the Half Cadence (ending on V), and the Plagal Cadence (IV to I). In a standard four-measure phrase, the cadence occurs at the end of the fourth measure. A Perfect Authentic Cadence (PAC) is the strongest, requiring both chords to be in root position and the soprano to end on the tonic. An Imperfect Authentic Cadence (IAC) is less final, often occurring in the middle of a piece. Recognizing where a phrase ends allows the student to work backward from the cadence, ensuring that the preceding chords (the predominant and dominant) lead naturally to the final resolution.
Figured bass realization AP questions (FRQ 2) require a precise translation of numerical shorthand into musical notation. A lone "6" indicates a first-inversion triad (6/3), while a "6/4" indicates a second-inversion triad. Seventh chords are represented by "7" (root position), "6/5" (first inversion), "4/3" (second inversion), or "4/2" (third inversion). Accidentals next to a number apply to that specific interval above the bass; a lone accidental (like a sharp or natural sign) always applies to the third above the bass. It is essential to remember that these figures are relative to the key signature. For example, in the key of C minor, a natural sign under a V chord indicates the raised leading tone (B natural), which is necessary for a functional dominant chord. Misinterpreting a single figure can lead to a "cascade" of errors in the subsequent voice leading.
A Step-by-Step Method for FRQ 2
To tackle FRQ 2 systematically, start by identifying the Roman numeral for each bass note based on the figures provided. Write these below the staff to serve as a roadmap. Next, determine the required notes for each chord. For the first chord, choose a starting position for the Soprano, Alto, and Tenor that is well-spaced and within range. As you move to the second chord, identify any common tones and keep them in the same voice if possible. For the remaining notes, move the voices by the smallest possible interval (stepwise). After completing each chord transition, immediately check for parallel fifths and octaves. This "measure-by-measure" verification prevents an error in the second measure from forcing a series of difficult-to-resolve problems in the final measures of the exercise.
One of the most frequent traps in figured bass is the treatment of the 4/2 chord (third-inversion seventh chord). Because the seventh of the chord is in the bass, that bass note must resolve down by step in the next measure. Another pitfall is forgetting to raise the leading tone in minor keys when the figures imply a major V or a diminished vii° chord. Students also often struggle with the "6" to "6/4" transition, where they might accidentally double the wrong note. To avoid these, always double-check the "legal" doubling for the specific inversion indicated by the figure. Finally, be wary of the "hidden" intervals in the figures; just because a figure only says "6" doesn't mean the 3rd and the 6th aren't there—the realization must still result in a complete triad unless otherwise specified.
Practicing with Past Free-Response Questions
Analyzing Scoring Guidelines and Sample Responses
The College Board publishes past exam questions along with detailed scoring rubrics and student samples. Reviewing these is the most effective way to understand how points are awarded. The scoring is often divided into "chord flow" and "voice leading." You can lose a point for an incorrect chord (wrong notes or wrong doubling) and another point for a voice leading error (like a parallel fifth). By studying high-scoring samples, you can see how successful candidates handle tricky transitions, such as the V to vi progression where the leading tone must go up and the third of the vi chord is often doubled to avoid parallels. Understanding the "point economy" of the exam helps you prioritize accuracy in the most heavily weighted areas.
Timed Practice for FRQ 1 and FRQ 2
Time management is a significant factor in the written portion of the AP exam. Students are typically given about 45 minutes for the entire written FRQ section, meaning you should aim to complete FRQ 1 and FRQ 2 in approximately 10 to 15 minutes each. During timed practice, focus on developing a shorthand for your work. Don't spend too much time erasing and rewriting; instead, use the Roman numeral analysis to "see" the chords before you write the notes. Practice under simulated exam conditions to build the mental stamina required to maintain strict adherence to voice leading rules even as the clock ticks down. The more "automatic" the rules of doubling and resolution become, the more time you will have to solve complex harmonic puzzles.
Self-Checking Your Work for Common Errors
After finishing a practice exercise, perform a systematic "audit" of your work. Check the Soprano and Bass first for any parallel motion. Then, check the Soprano and Alto, then Alto and Tenor, and so on, through all six possible voice pairings. Verify that every leading tone and every seventh has been resolved correctly. Ensure that no two voices have crossed (e.g., the Tenor is higher than the Alto) and that the spacing between the top three voices never exceeds an octave. Finally, play through your realization on a keyboard if possible; your ears will often catch a parallel fifth or a misspelled chord that your eyes missed. This self-correction process is the best way to internalize the rules and reduce the "silly" mistakes that often separate a 4 from a 5.
Beyond the Basics: Secondary Chords and Modulations
Integrating Secondary Dominants and Leading-Tone Chords
Advanced part writing involves the use of chromaticism through secondary dominants (e.g., V/V) and secondary leading-tone chords (e.g., vii°7/V). These chords are used to temporarily "tonicize" a chord other than the actual tonic. When writing these, the same rules of voice leading apply, but with the added complexity of accidentals. The temporary leading tone (the third of the V/V or the root of the vii°7/V) must resolve upward to the temporary tonic. For example, in the progression V/V to V in C major, the F# (the temporary leading tone) must resolve to G. These chords add harmonic color and are frequently tested in the later stages of FRQ realization to see if a student can maintain rule-following in a chromatic context.
Approaching a Temporary Tonic
When a secondary dominant is used, it creates a mini-cadence. The voice leading into and out of these chords must be handled with care to avoid awkward leaps. Often, the chromatic note (the accidental) is best approached by step or kept as a common tone if it appeared in a previous chord in its diatonic form. This is known as avoiding a cross-relation, where a note exists in its natural form in one voice and its chromatic form in another voice in the very next chord. For instance, if the Tenor has an F natural in a IV chord, the Tenor (not the Soprano) should ideally handle the F# if the next chord is a V/V. This ensures the chromaticism feels like a smooth inflection rather than a jarring shift.
Voice Leading Considerations for Altered Chords
In addition to secondary functions, the AP exam may touch upon other altered chords or modulations to closely related keys. When a modulation occurs, usually through a pivot chord (a chord that exists in both the old and new keys), the voice leading must remain seamless across the key change. The most important thing to remember is that the functional roles of the notes change: a note that was the "stable" tonic in the old key might become the "unstable" fourth scale degree in the new key. Staying aware of these shifting roles ensures that tendency tones are always resolved according to their function in the current key. Mastery of these advanced concepts demonstrates a high level of musical literacy and is the hallmark of a top-tier AP Music Theory student.