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In harmony, is it okay if there are consecutive 3rds in ii-V progression in two different bars?

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    Some of your notation is not up to scratch. A note only takes one space, if it is on a line then it takes half the space above and below the line. Too many of your notes take two spaces. A irratated examiner can deduct marks for that. The rules of notation are important. – Neil Meyer Jan 28 '18 at 9:46
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    Weird--the only note that looks too big for me is the C in the ii. – Dekkadeci Jan 28 '18 at 19:10

Yes consecutive 3rds are fine.

Consecutive 5ths, and octaves are a big no-no when doing voice leading and counterpoint, however consecutive 3rds and 6ths are fine (at least in moderation).

The reason for the distinction is when you have consecutive 5ths or octaves the voices that are in parallel sound like one unit and take away from the independence aspect of voice leading due to the purity of perfect intervals. 3rds and 6ths on the other hand still retain some independence in parallel due to the nature of the intervals.

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    Sometimes I wonder if the real reason for that rule wasn't mainly a reaction against organum (which is to say that parallel fifths sound medieval). :-) – dgatwood Jan 28 '18 at 6:08
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    @dgatwood there are definitely times you can use it effectively (look at power chords also in modern music), but specifically in voice leading it's all about independence. – Dom Jan 28 '18 at 6:11
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    Yeah, I was being snarky, in case it wasn't clear. :-) – dgatwood Jan 28 '18 at 6:44


The forbidden parallels regard most of the perfect consonances: unisons, fifths, and octaves. (Fourths are also perfect consonances, but parallel fourths are acceptable.)

But thirds and sixths are imperfect consonants and thus are not included in any rules regarding forbidden parallels.

Now, there's a broad rule in composition that you don't do the same thing more than three days in a row. So if you have parallel thirds, break them off before the fourth iteration. But this is a very soft rule and more of a recommendation than anything.

Lastly, the only thing to watch out for is the motion into the B chord on the downbeat. This is a very esoteric rule: between the soprano and bass, you have similar motion into a perfect fifth. When such similar motion has the soprano moving by step, this is okay. But if the soprano moves by leap, we call these "similar fifths," and some people (not all!) consider these forbidden.

PS: Note that you actually have three instances of consecutive thirds in this example:

  1. E/G♯ to F♯/A between the soprano and bass from I to ii
  2. A/C♯ to B/D♯ between the alto and tenor from ii to V
  3. B/D♯ to C♯/E between the alto and bass from V to vi
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    Careful, there. Parallel fourth motion isn't generally prohibited, because doing so would make many very common chord progressions very problematic (e.g. IV to V with the root of each chord in the middle). Parallel fourths should not, however, be overused. :-) – dgatwood Jan 28 '18 at 6:15
  • @dgatwood Oh, yikes; silly oversight on my part. Thanks! – Richard Jan 28 '18 at 14:27
  • Parallel 4ths often appear in 4-part writing aombined with parallel thirds. Like a string of first- or second-inversion triads. In real music - even for SATB, consecutive octaves and unisons are very common. But it happens when you decide to give EVERYBODY the tune (or the tune in parallel 3rds) and cop out of 4-part harmony for a bit! Within a 'harmony' section keep to the rules. – Laurence Payne Jan 28 '18 at 17:20

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