Consecutive sixths are three or more harmonic sixths sounding in succession between two voices. In 18th-century voice leading, parallel sixths (like parallel thirds) are acceptable, but long unbroken strings of them weaken the independence of voices the style demands.
Consecutive sixths happen when two voices move in parallel motion and keep forming the interval of a sixth, three or more times in a row. Picture the soprano and bass both stepping downward while staying a sixth apart for several beats. That's a string of consecutive sixths.
Here's the part that trips people up. Parallel motion isn't automatically wrong in 18th-century style. Parallel fifths and octaves are forbidden, but parallel sixths and thirds are perfectly legal. The catch is moderation. Voice leading in the common practice era is supposed to create independent voices (PIT-4.A.1), and if two parts shadow each other in sixths for too long, they stop sounding like two voices and start sounding like one thick melody. So consecutive sixths are fine in short bursts, but a long chain of them is a style red flag in part-writing, especially when you're composing a bass line under a given soprano.
This term lives in Topic 4.1, Harmony and Voice Leading I (Unit 4), and it connects directly to learning objective 4.1.A, identifying and applying 18th-century voice-leading procedures through score analysis, error detection, and writing. It also matters for 4.1.B and 4.1.E, where you compose a bass line beneath a given soprano. A bass that just rides a sixth below the soprano the whole phrase is easy to write but fails the melodic-interest standard in PIT-3.D.1, which calls for balancing steps and leaps and varying direction. Knowing that sixths are allowed (unlike fifths and octaves) but should be used in moderation is exactly the kind of judgment call the exam's part-writing FRQs reward.
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view galleryConsecutive Thirds (Unit 4)
Thirds are the inversion of sixths, and the same rule applies to both. A few in a row sound sweet, but a long chain glues the voices together and kills independence. If you understand one, you understand the other.
Parallel Fifths and Parallel Octaves (Unit 4)
These are the forbidden parallels. The contrast is the whole point. Sixths and thirds in parallel are stylistic, fifths and octaves in parallel are errors, because perfect intervals fuse two voices into one in a way imperfect consonances don't.
Contrary Motion (Unit 4)
The fix for too many consecutive sixths is usually contrary motion. When your soprano steps up, send the bass down. Mixing motion types is how you keep two parts sounding like two actual voices.
Melodic Interest in Bass Lines (Unit 4)
PIT-3.D.1 says a good bass line balances steps with leaps and up with down. A bass that tracks the soprano in sixths for a whole phrase technically avoids errors but flunks the interest test, which costs points on the bass-line composition FRQ.
Consecutive sixths show up in three places. First, error-detection questions can ask you to compare them against true errors, so you need to know that a passage with parallel sixths is correct while one with parallel fifths is not. Second, on the harmonization FRQ (composing a bass line for a given soprano), scoring guidelines reward voice independence and melodic interest, so leaning on sixths for more than about three consecutive intervals weakens your answer even though no single interval is wrong. Third, in score-analysis MCQs you may need to label the motion between two voices, and parallel sixths is a classic example of parallel motion that is stylistically acceptable. No released FRQ has used the phrase 'consecutive sixths' verbatim, but the underlying judgment is baked into every part-writing rubric.
Both involve two voices moving in parallel and keeping the same interval, but the verdict is opposite. Parallel fifths are always an error in 18th-century style because the perfect fifth is so acoustically stable that the voices fuse together. Parallel sixths are an imperfect consonance, so the voices keep some identity and the motion is allowed. The only issue with sixths is overuse. Three in a row is fine, a whole phrase of them is lazy writing.
Consecutive sixths means three or more harmonic sixths in a row between two voices moving in parallel motion.
Parallel sixths and thirds are allowed in 18th-century voice leading, while parallel fifths and octaves are forbidden.
Long strings of consecutive sixths weaken voice independence, which is a core goal of common-practice voice leading (PIT-4.A.1).
On the bass-line composition FRQ, break up chains of sixths with contrary or oblique motion to keep the bass melodically interesting.
A quick rule of thumb is that about three consecutive sixths is the comfortable limit before the texture starts sounding like one doubled melody.
Consecutive sixths are three or more harmonic sixths occurring in succession between two voices, meaning the voices move in parallel motion while staying a sixth apart. They're covered in Topic 4.1, Harmony and Voice Leading I.
No. Unlike parallel fifths and octaves, parallel sixths are legal in 18th-century style. The problem only appears when you write long chains of them, because the two voices lose their independence and start sounding like one thickened line.
Parallel fifths are always wrong in common-practice voice leading because the perfect fifth fuses the voices together. Sixths are imperfect consonances, so moving in parallel sixths is acceptable in moderation. Same motion type, opposite verdict.
There's no hard CED number, but the practical guideline is to keep strings of parallel sixths (or thirds) short, around three in a row, then change to contrary or oblique motion to restore voice independence.
On the FRQ where you compose a bass line for a given soprano, the rubric rewards independent voices and a melodically interesting bass. A bass that just shadows the soprano in sixths all phrase avoids interval errors but scores poorly on style and interest.
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