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The textbooks on classical harmony that I have read (Leo Semlek, "Klassikalise harmoonia lühiõpik" ["A Short Textbook on Classical Harmony"] and "Klassikalise harmoonia õpik" ["A Textbook on Classical Harmony"]) say that if V7 is in root position the fifth can be omitted (and the root is doubled).

There are some cases where he says that one should only use V7 without the fifth:

  • After II7
  • After IV

How does one decide when to omit the fifth? What is special about II7 and IV? In the case of II7, wouldn't it be a good idea to use the root of II7 as the fifth of V7?

I'm curious about the possible reasons because I am trying to write a computer program for generating nice classical chord progressions. It would be cleaner to have some kind of general rule ("omit the fifth if...") instead of adding several just-because special cases.

And are there any reasons why the textbook tells that the fifth can be omitted in V7 in root position but explicitly tells to not omit the fifth in the inversions of V7 or in any other seventh chord (II7 and VII7)? What is special about V7 in root position?

  • +1 for specifying "in classical harmony". Btw, have you listened to the examples, with/without omitting the fifth, can you hear any difference? I think if you cannot hear the difference, then it's a bit like cargo cult programming. ;) If you use rules, they should assist you in writing nice-sounding things straight away without having to go back to fixing the music all the time. But if you can't hear the difference... maybe try to find someone who can? :) Good question anyway. – piiperi Reinstate Monica Nov 25 '19 at 8:55
  • When you say II7, do you really mean the major-chord version (which is often better spelled in classical music as V7/V), or do you mean ii7? – Dekkadeci Nov 25 '19 at 12:45
  • @Dekkadeci Not all systems use capital vs. lowercase to denote mode. I would bet OP means the diatonic version, but hopefully they'll clarify. – Richard Nov 25 '19 at 13:09
  • @piiperi I can't hear the difference. But I'm not taking it as a sign that there is no difference, because I can also barely tell any difference between the tonic in root position and the cadential 6/4 chord, or between a dominant seventh and a dominant ninth chord... I'm also not bothered by parallel fifths unless there's a few of them in a row, but would still want my program to avoid them. (And strict rules would help contain the combinatorial explosion by pruning the less-desirable small fragments so that the number of longer fragments does not get out of hand.) – Liisi Nov 25 '19 at 14:08
  • @Dekkadeci Those textbooks use capital roman numerals for all chords. When talking specifically about minor (which he does rarely), those chords that contain the VI and VII degrees have superscripts that indicate whether the chord is natural or melodic/harmonic. So I'm assuming that when he talks about II7, he means the chord built from degrees II, IV, VI, I - and it can be a minor seventh chord (in major or melodic minor) or a diminished seventh chord (in harmonic minor). But I might be wrong about that. Not completely sure. – Liisi Nov 25 '19 at 14:20
1

The rule that the 5th can be omitted is developed of the voicing (voice leading) of the 4 parts:

ii7 = re,fa,la,do resolving:

re->so (bass root)

fa->fa (retain the common tone)

la->so (la->re could become a 5th parallel

do->ti (7th downwards)

similar problems with IV-V:

do->re (5th parallel with fa->so) ergo: do->ti

la->ti (ti would be doubling lead tone) ergo: la->so

if you keep the common tone and don't lead it downward there is no fifth in the V7 or you'll have strange leaps in the other parts (parallels of 5ths or the 7th of the succeeding chord won't be prepared or the 7th wouldn't be resolved correctly as lead tone.

The trouble with this rules is:

You should first write songs in this classical style and the you'll find the development of the rules by yourself. Other wise you have an amount of rules you should apply and don't know why. This means: Make first the mistakes and learn from your errors.

I suppose this program you want to write might already exist. Did you look it up yet?

  • 1
    Thank you. I forgot about the common tone. It's nice to know that those rules are not some random exceptions for no reason but corollaries of other, more understandable and general rules. About the program - yes, something similar probably already exists. But it's always fun to have an excuse to learn more about music theory and write some code :) – Liisi Nov 25 '19 at 15:18

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