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My understanding is that a dominant seventh can be substituted when going from V to I. so V7 to I. But are there any other situations where a seventh chord can be substituted for a triad?

I'm mainly talking in the context of a simple song that only uses triads, I'd like to add sevenths to spice things up. This question was inspired by a video I saw how they take a simple song (Amazing Grace) and then add more "colors" to it, mainly with sevenths.

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    Yes. Whenever the seventh chord sounds good. Looking for rules for everything is non-productive. Note that in the blues it is often the case that every chord is a dominant 7th chord. – David Bowling Sep 15 '18 at 16:33
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    @DavidBowling I mostly do things without rules by just how they sound, but I like asking on this site to find out if there are any rules. – foreyez Sep 15 '18 at 16:59
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    I'm a big fan of turning ii, iii, and vi triads into ii7, iii7, and vi7 chords in my playing. These are diatonic and the sevenths work in just about every situation where the triads do. In fact, I rarely (if ever) use just a ii or vi triad. – Kevin H Sep 15 '18 at 18:27
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    This is where ears can be very helpful. Far more helpful than trying to follow 'rules', which aren't rules, anyway. Just give them all a try, it won't hurt, you may even find something you like without being told 'this is what you have to do'. – Tim Sep 15 '18 at 20:00
  • It's not really a substitution, but there's a non-diatonic 7 in the chorus, "Oh I just (IV7) can't wait (V7)... To be king" in the Lion King. – The Chaz 2.0 Sep 15 '18 at 21:10
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By and large, yes: sevenths can be added to any triad in tonal music.

They're perhaps most common when the seventh chord resolves to a chord a fifth below it. But this is not a rule, merely an observation.

The only time where I would say a seventh could not be substituted for a triad is when that triad is the tonic chord that appears at a cadence. Since the goal of an authentic cadence is to reach a point of rest on tonic, we normally don't want to de-stabilize that tonic with a seventh.

However, if you have a specific musical goal in mind to weaken that cadential tonic, then you're welcome to put a seventh on it. This was especially common in the Baroque, when a tonic triad actually appeared as a V7/IV that started a coda that then led to another, more final cadence.

Lastly, when you get into "popular" music (that is, not Western art music), even tonics can have sevenths on them. We see this constantly in various jazz genres.

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    Major sevenths on the tonic get used a fair bit at the end of jazz tunes, when a perfect cadence occurs, so in total agreement. – Tim Sep 15 '18 at 20:02
  • If you find flat 7ths at the end of a resolved cadence, it's usually because they're implying the "harmonic seventh" rather than the "dominant seventh" (approximated by the same note in equal temperament"), which is a stable chord. For an example of this, think of the embellished "and many more" added to happy birthday, or the stereotypical completing a seventh chord at end of a major jingle in an ad. In C it would be "G A G Bb" with the Bb usually being a little flatter than usual when sung. – Some_Guy Sep 30 '18 at 5:50
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A general rule of how often to substitute sevenths by genre:

Blues - almost all chords have dominant sevenths

Jazz - most chords will have some sevenths, and sometimes further extensions (9, 11, 13), usually diatonic but not always, especially in jazz that has elements of the blues in it.

Classical - Mostly on the dominant chord (V7), but sometimes on the ii chord, and often on the leading tone (diminished 7th chord), and even the subdominant gets it sometimes. (Thanks to Richard, who commented below)

Metal - Never (mostly powerchords)

Rock - Depends on genre, but usually most rock is triads (with notable exceptions).

Electronic - Over most genres, sometimes minor chords will be minor 7ths to get a sort of airy feeling, but usually triads.

Pop - if there's a substitute dominant, it's a seventh almost every time. Sometimes sevenths will make an appearance, depending on how harmonically complex the song is.

Please note that these are just my opinions, and I could be wrong on some of them , but I've observed these general trends across my musical experience.

  • how could all chords in blues be dominant btw? wouldn't that produce notes outside of the scale? – foreyez Sep 15 '18 at 20:31
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    @foreyez - of course that produces notes outside the scale (non diatonic). So what? The blues pays scant notice to 'the rules' (whatever they're considered to be) anyway. Please move on from the 'must abide by the 'rules'' frame of mind. I fear it's impeding any normal progress as a musician. – Tim Sep 15 '18 at 21:20
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    These aren't your opinions but your observations, and as such perfectly valid here. Although I'd say your statements about classical and metal are a bit too narrow. – leftaroundabout Sep 15 '18 at 21:24
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    I'll respectfully disagree with the generalization of the Classical style you've given. Sevenths are found on the supertonic and leading tone constantly (certainly more than "rarely"), and even the seventh above the subdominant is relatively common. Sevenths above the mediant and submediant are, admittedly, rather rare. – Richard Sep 15 '18 at 21:25
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    @foreyez -- speaking for myself, at least, it isn't scoffing at rules so much as an attempt to assert that there are few, if any, rules to scoff at. It is great that you are asking questions about these things, but many on this site seem to ask questions that look for rule-bound advice where none exists. More stringent rules may be loosely associated with specific styles, but a more useful attitude is for you to invent the rules that work for you today. Then invent some new rules tomorrow. But, finding strategies to guide your playing is important; this may be where these questions are useful. – David Bowling Sep 15 '18 at 21:48
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A dominant seventh is good when the next chord is a step or half step above in a (perhaps tonicized) deceptive cadence. A G7 chord goes nicely to an Am.

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You can use the seventh of any of the seven diatonic chords in a scale. I would just personally avoid using the Tonic chords seventh as that seventh is also the leading tone of the scale which makes for a problematic resolution.

My question is just why would you not want to use the sevenths of chords they give such great colour to a chord why omit them? You are greatly stifling your own creativity by not using them as a matter of principle.

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