Soprano moves from C5 to D5 while alto simultaneously moves from G4 to A4 — both voices moving up by a major second, with the interval between them remaining a perfect fifth throughout. What voice-leading error has occurred?
ANo error — parallel motion is only forbidden between the soprano and bass
BParallel fifths — two voices moving in the same direction while maintaining a perfect fifth, collapsing their independence into a single composite sound
CHidden fifths — the voices don't arrive on a fifth, so this is only a mild concern
DVoice crossing — the voices have moved into each other's range
This is parallel fifths: two voices moving in the same direction (both up) while preserving a perfect fifth between them. The prohibition exists because parallel fifths fuse two voices into a single, thicker sound — they stop behaving as independent melodic lines. The listener hears one voice doubled at a fifth rather than two distinct contrapuntal voices. The rule applies between any two voices, not just soprano and bass, though parallel motion in the outer voices is particularly exposed.
Question 2 Multiple Choice
A student analyzes a Bach chorale and marks a perfect fourth (P4) between soprano and bass as an error, citing the rule that fourths between outer voices are forbidden. Is the student correct?
AYes — any P4 between soprano and bass is always a voice-leading error in SATB writing
BNot necessarily — a P4 between outer voices is acceptable when the bass note is not the root of the chord (i.e., when the chord is in an inversion other than root position)
CNo — P4 between outer voices is always acceptable because fourths are consonant intervals
DYes, but only when the P4 is approached by contrary motion
This is one of the most commonly misapplied rules in four-part writing. The prohibition on P4 between outer voices applies specifically when the bass holds the root of the chord — in that context, the fourth above the bass creates an unstable, unresolved sound that demands treatment. When the chord is inverted (the bass holds the third or fifth), the same P4 interval is perfectly acceptable. Bach uses this constantly. Blanket application of the rule without understanding its harmonic context will flag legitimate writing as errors.
Question 3 True / False
The prohibition on parallel fifths and octaves in four-part writing exists primarily to preserve the independence of each voice as a distinct melodic line.
TTrue
FFalse
Answer: True
True — this is the underlying principle. When two voices move in parallel to a perfect fifth or octave, they begin to blend into a single sound rather than functioning as two independent contrapuntal lines. The entire purpose of four-part writing is to maintain four distinct, singable, melodically interesting voices simultaneously. Parallel motion at these intervals defeats that purpose by acoustically fusing two of those voices. The rule is not aesthetic whim; it follows from the psychoacoustics of how the ear groups simultaneous sounds.
Question 4 True / False
In four-part SATB writing, the three upper voices (soprano, alto, tenor) is expected to most remain within an octave of the bass voice.
TTrue
FFalse
Answer: False
False — the spacing rule applies to the three upper voices relative to each other: soprano, alto, and tenor should generally stay within an octave of each other. The bass voice may sit considerably further below the tenor without violating spacing rules. This is why large gaps between bass and tenor (even two octaves) appear regularly in Bach chorales, while gaps larger than an octave between any two adjacent upper voices are typically avoided. Misapplying this rule to the bass will cause you to flag correct writing as errors.
Question 5 Short Answer
Why are parallel fifths and octaves prohibited in four-part writing? Explain what they do to the texture and why that matters.
Think about your answer, then reveal below.
Model answer: Parallel fifths and octaves cause two voices to move as a single entity — the interval between them stays fixed, so the ear hears one voice doubled at a fifth or octave rather than two independently moving melodic lines. Four-part writing derives its richness from the simultaneous independence of four voices, each tracing its own melodic path. Parallel fifths collapse this into three effective lines (or fewer), reducing contrapuntal interest and the sense of harmonic fullness. The prohibition is ultimately a rule about voice independence: each line must behave as a distinct, self-contained melodic entity. This is grounded in psychoacoustics — the human ear groups sounds moving in fixed parallel ratios into a single composite source.
Understanding the principle behind the rule — voice independence — is more useful than memorizing the rule itself, because it lets you evaluate edge cases (e.g., brief parallel fifths in fast passing motion) and understand why Bach occasionally bends the rule when the musical context justifies it. The Common Misconceptions section notes that voice-leading rules are 'learned principles that can be broken strategically for musical effect when justified' — knowing the WHY makes you a better judge of when that justification applies.