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To what keys do chords like C6, C6/9 , Gm7b5 or dominant 7 sharp ninth chords, suspended chords, power chords, belong to?

Note: I don't specifically mean C6, I'm more focused on the type of chord and not the chord itself.

For that matter, apart from the minor, major, seventh and diminished chords in every key, how do I determine in which key do the other chords (like 6th chords, ninth chords, dominant 9, dominant minor 9) belong to?

Edit: ( I wasn't clear earlier)

What I meant was, for example when we Google "chords in C major" we get the I-vii° chords of C major and the added 7th chords. This goes for any key that I Google. But what about the fancier chords like C6/9, dominant 7sharp 9, and all those jazz chords? I've never seen these chords pop up when someone Googles for chords in a key. So I was wondering to what chords these keys belong to and how one goes about determining that.

Edit edit: to be more clear, I tried to put many doubts into one question and hence the confusion. I'd rather just split the entire question into subdivisions.

1) a dominant 7 sharp 9 chord belongs to which key? Eg: Gdom7#9

2) a suspended chord belongs to which key?

3) a power chord belongs to which key? And how do you determine it?

4) a ninth chord or 6/9 chord belongs to which key? And how do you determine it?

closed as too broad by ex nihilo, Richard, Tim, Doktor Mayhem Jan 11 at 11:13

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    Most belong to the major scale or key. Some are altered, or belong to melodic minor. I think your question is way too broad. Are you look for a key that contains both C6/9 and Bm7b5? Please specify more details and bound the question. I may vote to close it. – ggcg Dec 21 '18 at 12:09
  • You'll need to be a lot clearer! Generally, we'll find something like C dominant7#9 in either its own key (C) or its subdominant key (F). But the question isn't clear. – Tim Dec 21 '18 at 12:11
  • @tim sorry for not being clear. What I meant was, for example when we Google "chords in C major" we get the I-vii° chords of C major and the added 7th chords. This goes for any key that I Google. But what about the fancier chords like C6/9, dominant 7sharp 9, and all those jazz chords? I've never seen these chords pop up when someone Googles for chords in a key. So I was wondering to what chords these keys belong to and how one goes about determining that. – noorav Dec 21 '18 at 12:16
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    Use them whenever you feel the need. There are NO hard and fast rules. All Google can tell you is the diatonic chords from a key. Even that's not strict. They're just 'jazz' chords - extensions of basic chords, which may or may not sound good in certain places. Try not to be fenced in by following 'rules', it's far too restrictive, and you'll start to wonder why what you're playing is sounding bland!! – Tim Dec 21 '18 at 12:23
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Don't confuse 'diatonic chords' with 'chords that are used in a song in a particular key'. Once again, I'll pull out one of my favourite quotes (the other one is 'Theory describes, it does not command'):

'Notes outside the scale do not necessarily affect the tonality'. Walter Piston, Harmony.

Consider this common progression: C, C7, F, Fm, G/C, G7, C.

Plenty of notes there that are not in the C major scale. But it would be ridiculous to analyse it as a series of micro-modulations, we never stop being 'in the key of C'. We don't need to resort to 'borrowing' either. I7, iv are part of C major just as much as are the diatonic chords. They COULD be gateways to another key-centre, but in this case they aren't.

Let's try some 'jazz chords'. C, F, G, G7, C. 'In C major', right? Change the G7 to G7b9, G13(#5,#11) or even Db7 (a 'tritone substitute' of G7.) Still 'in C major' though.

You couldn't make an exhaustive list of chords 'in C major'. It would include SO many chords!

As always, context is all. YOU have to decide whether a chromatic chord is part of a modulation, or if it's just adding colour (which is what 'chromatic' means) to the key we started in.

  • just to clarify, so what you're trying say is jazz chords don't have a particular "key" but are used just to add flavour? – noorav Dec 21 '18 at 13:33
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    Not many chords have a fixed 'key'. Most of them ('jazz' or otherwise) can find a function in many keys. Take off the straitjacket of the diatonic scale, and the chords you can construct from it. It's a framework, not a restriction. – Laurence Payne Dec 21 '18 at 13:53
  • The key of the chord depends on context and function, not on the particular notes of the chord. The notes of an Am chord may function as the tonic in Am or a D9 in G or a Fmaj7 in C, It depends on the context and function. . . – PeterJ Dec 21 '18 at 13:59
  • Maybe you meant to say C, C7, F, Fm, G/C, G7, C ? – piiperi Dec 21 '18 at 14:31
  • Your example of the jazz tritone substitution illustrates the point very well: chromatic chords don't disturb the tonality, and the basic tonality (I mean the diatonic scale) isn't a definition of available chords. – Michael Curtis Dec 21 '18 at 18:53
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Theoretically, any chord that only contains notes that are in the key will be "in that key".

Let's use C major as our example scale (because it's easy and OP mentioned it).

1) a dominant 7 sharp 9 chord belongs to which key? Eg: Gdom7#9

Dominant 7 sharp ninth chords are actually never diatonic in any key. However, they are commonly substituted as the V in minor, so E7♯9 in A minor is pretty standard (harmonic minor).

2) a suspended chord belongs to which key?

Okay, in C major, the diatonic suspended 4th chords are built on C, D, E, G, and A. Sus2 chords are the same as sus4 chords on a different root. This can be generalised to any key.

3) a power chord belongs to which key? And how do you determine it?

Power chords are so ambiguous, you can build them on any scale degree except the vii. You can't tell without context what key a power chord is in; there's not enough harmonic information.

4) a ninth chord or 6/9 chord belongs to which key? And how do you determine it?

9th chords? There's a whole list of diatonic 9th chords right here: https://music.stackexchange.com/a/74558/45266

6/9 chords are different. They have less of a function, and like most chord types, they don't point to any key in particular without context. In C, you can build them on C, F, and G. If you leave out the 3rd, you can also use D.

In general, chords belong to the key they are written in. Unless it's some huge 13th chord, you can't tell which key is implied by a chord. Bm could be part of B minor, or it could be part of G major, or plenty of others.

To address concerns about my answer:

I'm not arguing that only chords that are in a key can be used. There are of course many ways to use chords nondiatonically, and using them that way obviously doesn't change the key of the piece. But if you allow non-diatonic chord usages, then that just 'opens the book too wide' and you could claim any chord belongs to any key, a rather useless stance. My point is, sure, you can use C♯dim7 in C major. Or F7 and C7. But those chords aren't from C major. They don't belong to C major. And that's okay.

  • It's clear, but I'm afraid it's wrong. Chromatic notes and chords don't necessarily change the key. Take a simple C, C#dim7, Dm7, G7, C progression. It never leaves C major. C#dim7 is #Idim7 in C. Or look at a simple blues. C7, F7, G7, C7. It's a blues in C. Despite the Bb and Eb, it doesn't keep changing key! – Laurence Payne Dec 22 '18 at 22:24
  • The first sentence is misleading. It suggests that we must look for some other key to justify a chromatic chord. It doesn't matter that a chord may be diatonic in some OTHER key. We're in THIS key! – Laurence Payne Dec 23 '18 at 15:47
  • @LaurencePayne I agree; see my edit. You may have missed my point. – user45266 Jan 7 at 1:16
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Extended chords do appear naturally "in key". Chords are generated by stacking thirds {1, 3, 5, 7, 9, 11, 13}. In some sense they are the scale played in thirds instead of seconds. This does not explain the occasional altered chord but for example the 6th and 6/9 chords occur naturally without going out of key.

Some of the more interesting jazz chords do arise naturally from the melodic minor scale. You can do the analysis yourself and see which ones pop out.

However, we do use "accidentals" in music. The introduction of an out of key note in a chord will likely serve a purpose in (1) harmonizing an out of key melody note in the head, or (2) serving as a leading note to something in the next chord of a sequence, (3) just sounds cool and doesn't have a theoretical explanation using the rules of western music theory. In many cases chords are altered in a sequence to produce chromatic lines within the movement of the multiple voices. There is a plethora of examples of the device in all guitar method books (and piano too I'm sure, but guitar is my instrument).

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Laurence Payne's answer is very good and comprehensive. I'll just add this (hopefully funny or thought-provoking) example, which to me feels like just a simple I-VI-II-V-III-VI-II-V-I in C, it's just pimped with "jazzy" seasoning tricks. (enharmonic spellings might be "wrong", it's just the default stuff Sibelius did to MIDI input)

Chords in C

If you play a C note, I think you'll agree that that was the key-center all the time? There seem to be weird notes and chords, but the key-center doesn't really move away from C, in my opinion. There's a tritone substitution that tries to disguise the final dominant, but ... nah, simple bread-and-butter chord progression in C. Whatever the chords are, they do their job in this context, without creating a sense of modulation (YMMV). So couldn't it be justifiably said that all the chords belong in the key, in some way? You could argue that it's somewhat subjective, but isn't everything in music. :)

Edit: I'll add another example. Let's take out the bass notes, which might give the key away too easily. For example, look at the second chord. It's an F#/C#, so would you guess the key is C major? same example without bass notes

  • Yes, this is basically a 'cycle of 5ths' progression in C. Some would want to analyze it as a bunch of 'temporary tonics'. I really don't see the point. – Laurence Payne Dec 24 '18 at 2:03
  • @LaurencePayne The point was to highlight the weirdness of the OP's question, which to me seemed like asking for rules for figuring out the key when given a chord. "This chord, so what key?" That's not possible. My example would be even better, if the bass notes were left out. In order to figure out the tonality particularly for jazzy stuff that modulates, you have to take the whole context into account. The harmonic effect of a note, or a group of notes i.e. a chord, depends on the prevailing situation, i.e. what happened before it and what the expectations are. – piiperi Dec 24 '18 at 11:02

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