The soprano moves from G up to D (a fifth higher), and the bass moves from C up to G (a fifth higher). Is this a voice-leading error in common-practice four-part writing?
ANo — soprano and bass are in contrary motion, so no error occurs
BYes — this is parallel fifths: both voices move upward by a fifth
CNo — parallel fifths only matter between inner voices
DYes — but only if the interval between soprano and bass was already a fifth before the motion
Both voices move upward, and the interval between them is a perfect fifth both before (G–C? No — wait: soprano G to D and bass C to G). Let's be precise: soprano G–D is a perfect fifth, bass C–G is a perfect fifth, both moving in the same direction (up). The previous soprano-bass interval (soprano G, bass C) is a perfect fourth, but what matters is the motion: both voices move up and land on a perfect fifth (soprano D, bass G). This produces parallel fifths — the defining error. Option A is wrong because contrary motion would require one voice to go up while the other goes down.
Question 2 Multiple Choice
Why are parallel perfect fifths and octaves forbidden in common-practice four-part writing?
ABecause they are dissonant intervals that create unpleasant harshness
BBecause they were arbitrarily chosen as errors during the Baroque period with no acoustic justification
CBecause they cause the two voices to acoustically fuse, collapsing four independent lines into fewer distinct strands
DBecause they produce unresolved leading tones that weaken tonal direction
Parallel perfect intervals are forbidden precisely because of acoustic fusion, not dissonance. Perfect fifths and octaves are the most consonant intervals (simple frequency ratios), which is exactly why parallels are problematic: two voices moving in parallel perfect consonance blend so completely that they sound like a single reinforced voice, not two independent lines. The style's governing ideal is four distinct melodic strands; parallel fifths or octaves momentarily reduce the texture from four to three (or fewer) effective voices. Contrary fifths — arriving at a fifth from opposite directions — are perfectly acceptable.
Question 3 True / False
Parallel fifths are a voice-leading error that should be avoided in most musical styles and traditions.
TTrue
FFalse
Answer: False
Parallel fifths are specifically forbidden in common-practice tonal harmony (roughly Baroque through Romantic eras) where independent voice leading is the governing ideal. They appear intentionally in medieval organum (where parallel perfect intervals were the compositional style), in modal folk music, in Debussy's impressionist parallel chord streams, in jazz and popular music, and in contemporary composition. Understanding this restriction as style-specific, not universal, is essential: the rule belongs to a particular tradition and its particular aesthetic values.
Question 4 True / False
Two voices that arrive at a perfect fifth by moving in contrary motion violate standard voice-leading rules.
TTrue
FFalse
Answer: False
The prohibition is specifically on *parallel* motion to perfect intervals — both voices moving in the same direction. Contrary motion means one voice ascends while the other descends. Two voices approaching a perfect fifth from contrary directions is not only acceptable but often preferred, as it creates a sense of arrival without fusion. The error is entirely about the direction of motion: same direction produces parallel (forbidden); opposite directions produces contrary (fine).
Question 5 Short Answer
Explain why parallel perfect intervals cause a perceptual problem in four-part writing, in terms of what the listener experiences.
Think about your answer, then reveal below.
Model answer: When two voices move in parallel perfect intervals (fifths or octaves), they acoustically fuse — the listener hears them as a single reinforced line rather than two independent melodic strands. Perfect intervals have the simplest frequency ratios (2:1 for octaves, 3:2 for fifths), making them the most consonant and the most prone to blending. In a four-voice texture aiming for independence — where each voice has its own melodic identity — this fusion momentarily collapses the texture. The four distinct parts reduce to three or fewer audible strands, contradicting the style's fundamental premise.
The acoustic explanation grounds the rule in perception rather than arbitrary convention. This is why the same intervals are celebrated in medieval organum (where fusion was the goal) and forbidden in Baroque counterpoint (where independence is the goal). Recognizing that the rule is style-specific and perceptually motivated helps musicians apply it intelligently rather than mechanically.