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I noticed that secondary dominants are usually dominant seventh chords. Can you just make a secondary dominant a triad, or is it "required" to make it a seventh chord? (also I think this chord is always major).

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    always amazed at the answers I get on this forum, thank u all so much – foreyez Jan 18 at 15:04
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No, secondary dominants aren't required to be seventh chords. They can be plain triads (e.g. V/vi). They also aren't required to be major or have a major triad--I've heard plenty of vii°7/V chords, and those are diminished 7th chords.

  • The "vii°7" would be the Barry Harris style dominant. Barry Harris seems to be somewhat of a hot (or at least lukewarm) topic on teh interwebz. – piiperi Jan 18 at 7:51
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    I think the point is the secondary dominant needs a leading tone, effectively either a V or a viio with or without 7th or 9ths. But a minor chord wouldn't be a secondary dominant for its lack of a leading tone. – Michael Curtis Jan 18 at 17:51
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The fact that a secondary dominant, when a major triad, has a M3 in it, which usually moves to the root of the next chord (V) is sufficient. With that b7, there's the tritone which convincingly moves things on, but not needed. And as @piiperi says, that secondary dominant doesn't even need to be major or minor - diminished chords have the propensity to act as pivotal chords in their own right, and take the music into other modulations.

Even when the v/V is minor, there's still enough scope for it to work, as it sometimes does when something in a minor key only uses natural minor notes. Not as convincing, but still feasible. It's good that we are now moving away from the concept of rigid rules, which don't exist these days! I nearly said never, but a few centuries ago, adherence was expected!

  • Isn't a v/V just a normal ii chord? Even if we're in a minor key, I would describe that chord as a use of mode mixture. The leading tone is really necessary create the effect of a secondary dominant. – Peter Jan 18 at 18:03
  • @Peter - v/V is the same chord as ii. True. The Roman numerals help to define not only the chord, but its function. V doesn't always follow v/V, but when it does, that ii takes on the role of secondary dominant - as in v/V. – Tim Jan 18 at 20:12
  • I can't agree with you on this. The ii chord preceding a V acts as a subdominant (like a IV), which is a distinct function from a secondary dominant. – Peter Jan 18 at 20:45
  • @Peter the subdominant in key C is F. The secondary dominant is Dm (or D/D7 or Dm7). Common notes abound. True. But its function is as a dominant leading to a dominant. Thus the term secondary dominant. That's it. – Tim Jan 18 at 21:11
  • We'll have to agree to disagree. Your interpretation does not match with any definition of secondary dominant that I've ever seen. – Peter Jan 18 at 21:39
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A secondary dominant "tonicizes" the chord that follows it, temporarily making it sound like a I chord. So, the secondary dominant needs to lead into that chord. A V chord can do this with the third of the chord, which acts as a leading tone into the root of the following chord. It does not need the 7th of the chord, but that will increase the pull with the existence of the tritone between the 3rd and 7th of the chord. A diminished vii chord can also be used because it contains the leading tone going into the next chord (the root of the vii chord), in addition to the existing tritone in the diminished chord. It is basically the upper portion of a V7 chord, without the root.

A V chord or a diminished vii triad really only point towards one tonic. However, if a fully diminished vii7 is used, there are more possibilities. There are four different tritones in a fully diminished seventh chord, which could point towards four different tonics. For example, D F Ab Cb could "tonicize" Eb, F#, A, or C (and their enharmonic equivalents) depending on how it is interpreted. If more flexibility is desired with a diminished chord, the 7th needs to be used.

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The answer is:NO

while the (V7) is almost always used: in jazz (IIm7 - V7) the proper V is rarely found (as in folk tunes in a choir setting or in church choral settings *)

I just went through some Bach-preludes and didn't find a proper V.

They V will appear in a SATB voicing like:

Oh du fröhliche Weihnachtszeit

enter image description here

  • The OP asked about the secondary dominant, not the dominant. – Tim Jan 18 at 9:56
  • yes, I forgot the ( ) thanks, Tim. In the sheet example it is clear that I am relating to this. – Albrecht Hügli Jan 18 at 10:22
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Most people have stated here that you don't need the seventh to create a secondary dominant sound. That's true, as listening to D, G, C makes sense and sounds arguably just as good as D7, G7, C. But, there's one exception!

V7/IV must contain the seventh degree. In A major, one must use A7 to resolve to D, otherwise it's not a secondary dominant at all. Any other secondary dominant doesn't matter, because without the seventh they aren't diatonic, but V/IV is I7, and I is diatonic and so won't be heard as a secondary dominant unless the minor seventh is added over it.

Dekkadeci recently made me aware (thank you) that in minor keys, V/iv would not need the seventh (In A minor, A major to D minor doesn't need the seventh).

  • Note that the similar V/iv can get away without a seventh in a minor-key context, as another reading of it is the alien-in-a-minor-key I (instead of i). – Dekkadeci Jan 18 at 17:42
  • @user45266 but if you precede the A with, say, a Gm6/E (a.k.a. Em7b5) or Em7 or G or just an Em, then the A works as a secondary dominant even without a 7th. :) (you'll probably say that it's because the preceding chord at least temporarily established the presence of a G) – piiperi Jan 18 at 18:10
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"Required" by what? Are you referring to some cultural convention or a law of nature or what? ;)

Wikipedia's example shows a D major without a seventh: https://en.wikipedia.org/wiki/Secondary_chord

In this example, I think the F# note alone works in some kind of a secondary dominant'ish function, even though it's not even a chord.

what is required for what

On the next line I added more simultaneous notes, leaving less room for imagination. Do these sound secondary-dominantish enough to you?

Some more: enter image description here

To my ear, the one with the C-F# tritone gives the strongest secondary dominant vibes, followed by the D-F# version. There are at least two ways to think about it. What is the implied "true" chord there - is it D7, or ... F#dim7? In the Barry Harris way of thinking, the dim7 is the "real" dominant.

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    Are you referring to some cultural convention or a law of nature or what? - it's a question about terminology, so presumably it's just asking what's commonly understood by the term..? – topo morto Jan 18 at 8:17
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    @topomorto I want to teach a man to fish instead of just giving him a fish. – piiperi Jan 18 at 9:31

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