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If I take the augmented sixth chord Ab-C-F#, why is its dominant G? This augmented chord is in the F minor scale, isn't it? But isn't G the dominant in C? Maybe I missed something on how to understand the build up of augmented chords?

Richard
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LoveIsHere
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  • The aug 6th note is the same sound, different name , as the b7, so Ab C F# writes better as Ab C Gb. 'Its dominant is G' don't understand.The usual note augmented in chords is 5, so why there would be an aug6th chord, I don't know. And an aug minor chord? Say Cm+, (root) it's really Ab major 1st inv.). Yes, I'd say you missed something, but exactly what, can't tell right now. Sorry. Try re-phrasing the question please. – Tim Jun 04 '17 at 12:00
  • By "its dominant is G," I think the user means "the tonal center for this chord is G major." He has spelled the chord correctly, and it could be called Ab augmented 6 or Ab7. Jazz folks will want to think of it as Ab7 because then we see that this chord is a tritone substitution for D7, the V to G major. – jdjazz Jun 10 '17 at 01:01
  • To clarify for others reading: augmented-sixth chords don't "resolve" to the dominant, but rather *progress*. Augmentexd-sixth chords serve as pre-dominants to the dominant. It is the dominant that resolves the progression. – jjmusicnotes Jun 10 '17 at 13:33

3 Answers3

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An augmented-sixth chord typically precedes a dominant. These augmented-sixth chords are so named because of the augmented-sixth interval between two of its pitches (in this case, between A♭ and F♯). These two pitches then move in contrary motion by semitone to reach scale-degree 5 of the key. Thus A♭ moves down a half step to G and F♯ moves up a half step to G. Since G is scale-degree 5 of C, we're looking at an augmented-sixth chord in C. This is why G is "the dominant" of your A♭–C–F♯ augmented-sixth chord.

The collection A♭–C–F♯ is not in the F-minor scale, since there is no F♯ in F minor.

You can also build an augmented-sixth chord backwards, by starting on the dominant. If we're in C, our scale-degree 5 is G. Now go up a half step from G and put that pitch (A♭; this is scale-degree ♭6) in the bass, then go down a half step from G and put that pitch (F♯; this is scale-degree ♯4) in an upper voice. Voila, there's your augmented-sixth interval, from which you can fill in your augmented-sixth chord.

Now, there are three types of augmented-sixth chords. All of them have that augmented-sixth interval between scale-degrees ♭6 and ♯4. They also all have scale-degree 1.

  • If you just have those three pitches, we call it an Italian augmented-sixth chord.
  • If you have those three pitches but add in scale-degree 2 (D in the key of C), we call it a French augmented-sixth chord.
  • If you have those three pitches but add in scale-degree ♭3 (E♭ in the key of C), we call it a German augmented-sixth chord.
Richard
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  • HI Richard, thanks for the explanation and sorry for the late comment was sure it wasn't answered. I was sure it is in f minor because I read you take a chord in minor such as F-Ab-C. do a first inversion where the distance between ab and f is six, then raise the f in semitone to f# to get the augmented six chord. – LoveIsHere Jun 22 '17 at 06:00
  • In your explanation, there is no C in the chord of G unless only the root note is called the dominant and also there is no f# in c major scale. but if I follow exactly your explanation about lowering and raising semitone in both directions to get the G chord I guess that make sense but again then the six augmented chord is totally not related to c major scale....?! – LoveIsHere Jun 22 '17 at 06:09
  • Correct, there is no C in the G chord. But (if I understand you) augmented-sixth chords resolve to dominant chords. And since this augmented-sixth chord resolves to G, that G is the dominant of C, so this chord is an augmented-sixth chord in C. However, augmented-sixth chords are *chromatic* chords, meaning that they use pitches outside of given major or minor scales. So no, this chord isn't that closely related to the C-major scale, even though it functions in C! – Richard Jun 22 '17 at 16:31
  • cool thanks, now it's clearer. i also read somewhere that it can be the dominant of c minor key. in that way this augmented 6 is closely related to c minor key (inversion of an f minor with a raised f to f#) :). – LoveIsHere Jun 23 '17 at 14:06
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There's a really simple reason why this sounds good and thus is found in music theory. D7 (which is the V to G maj) is spelled D F♯ A C, and A♭7 (the chord you've cited) is spelled A♭ C E♭ G♭. In both cases, we've spelled the chords using the 1st, 3rd, 5th, and 7th scale tones. The crucial fact here is that D7 and A♭7 share the exact same notes as their third and seventh. For both D7 and A♭7, the 3rd and 7th are C and F♯ / G♭.

Why does sharing the 3rd and 7th make | A♭7 | G maj | sound as good | D7 | G maj |? Besides the root, the 3rd and 7th are the most important tones for defining the quality of a chord. The presence of a flat vs. natural third and a flat vs. natural seventh distinguish major chords from minor chords from melodic minor chords from dominant seventh chords.* The 3rd and 7th are of crucial importance, and so any two chords which share the same 3rd and 7th are in a way interchangeable.

In fact, in jazz, taking a V–I progression like | D7 | G maj | and substituting in | A♭7 | G maj | is called a tritone substitution and is probably the most common chord substitution in the entire genre. This is called a tritone substitution because we're replacing D7 with a chord that is exactly a tritone (six half steps) away. A♭7 is in the key of D♭ maj, which is similarly a tritone away from the G maj tonal center.

In classical music, the traditional approach is for this chord (augmented sixth) to resolve to a dominant chord, not a major chord as I've shown above. So the classical music progression would be: | A♭7 | G7 | C Maj | or | D7 | D♭7 | G♭ Maj |. Additionally, classical musicians wouldn't call the first chord a dominant seventh chord--they would recognize the function it was serving and use that function to distinguish it as an 'augmented sixth' chord. This gives: | A♭ aug 6 | G7 | C Maj | or | D aug 6 | D♭7 | G♭ Maj |. Jazz theory doesn't draw this distinction and calls the first chord a dominant 7th chord.

*See below for distinctions based on the 3rd and 7th:

  • major chord: natural 3rd, natural 7th
  • minor chord: flat 3rd, flat 7th
  • melodic minor chord: flat 3rd, natural 7th
  • dominant 7th chord: natural 3rd, flat 7th
jdjazz
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  • beautiful answer thanks a lot! what did you mean when you wrote : "A♭7 is in the key of D♭ Maj, which is similarly a tritone away from the G Maj tonal center". I understand the tritone distance from db to ab but what does it mean that it is a tritone from the g major tonal center? – LoveIsHere Jun 22 '17 at 06:29
  • Thanks! "Tritone" is a jazz term used to describe an interval consisting of of 3 whole steps. It's the exact same as a raised fifth (or augmented fifth). The chord A♭7 is spelled A♭ C E♭ G♭, and this chord has the same notes in its scale as D♭ Maj. The chord D7 is spelled D F♯ A C, and this chord has the same notes in it's scale as G maj. We can consider the two dominant seventh chords (A♭7 and D7), and ask this question: what's the interval between their roots (A♭ and D)? The answer is "a raised fifth / a tritone." We get the same answer for the interval between the roots of G Maj and D♭ Maj. – jdjazz Jun 22 '17 at 13:08
  • The scale for G Maj is G A B C D E F♯ G. The scale for D♭ Maj is D♭ E♭ F G♭ A♭ B♭ C D♭. The two scales only share two notes: C and F♯. They are as different as two major scales can possibly be, and yet they share two crucial notes that allow these major I chords (G Maj and D♭) to have interchangeable V7 chords (D7 and A♭7). So instead of playing the normal chords D7 - G Maj or A♭7 - D♭ Maj, you can swap out the V7 chords because they have the same notes as their 3rd and 7th. Making this swap gives us two new progressions: A♭7 - G Maj and D7 - D♭ Maj. This swap is called a tritone substitution. – jdjazz Jun 22 '17 at 13:40
  • In classical music, the traditional approach is for this chord (augmented sixth) to resolve to a dominant chord, not a major chord as I've shown in my answer and comment. So the classical music progression would be: A♭7 - G7 - C Maj or D7 - D♭7 - G♭ Maj. Except classical musicians wouldn't call the first chord a dominant seventh chord--they would see the function it was serving and use that to distinguish it as an augmented sixth chord. This gives: A♭ aug 6 - G7 - C Maj or D aug 6 - D♭7 - G♭ Maj. Jazz theory doesn't draw this distinction and calls the first chord a dominant 7th chord. – jdjazz Jun 22 '17 at 13:56
  • wahoo it's absolutely magical! I really got this now thanks!! by the way after a small research on my piano I saw that only dominant 7th chords where the 3rd and 7th notes are a tritone apart share them with another chord am I right? – LoveIsHere Jun 23 '17 at 14:57
  • Yes, that's exactly right--for traditional harmony, only dominant chords will have the same 3rd and 7th when you modulate a tritone away. The other chord, which is perhaps an exception, is a diminished chord. For example, C dim and F# dim both have Eb and A and the 3rd and 7th. – jdjazz Jun 23 '17 at 15:21
  • right diminished also! brilliant JD:) – LoveIsHere Jun 23 '17 at 16:13
  • you mean to check the upper button on the left side? would love to do it but I don't have enough reputation. it doesn't let me...or did you mean something else? – LoveIsHere Jun 23 '17 at 16:40
  • ohh i found it ! it is not clear enough and almost hiden. i checked it. big yes! – LoveIsHere Jun 23 '17 at 19:06
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    What a great answer, especially because you mentioned how the same chord is treated in both classical and jazz music. When I asked my harmony teacher two months ago, if I could write `C | Db7 | C`, he replied "Not in classical music!" However, I think it's important to mention the fact that Schubert uses the tritone substitution in his String Quintet in C major, D. 956, at the end of the final movement. – George Apr 19 '18 at 20:23
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As so often when attempting to explain tonal harmony - a clue is 'hunt the tritone'. C and F# (however we spell them) are a tritone that want to resolve to B and G. This tritone interval occurs in D7 (which we all know resolves to G). But it's in the Aug6 chord as well.

The next stage is to realise that a tritone is symmetrical. It can resolve two ways. C and F# (Gb) can resolve to a Db chord - think of them as the engine of Ab7. (And that Aug6 chord looks a lot like Ab7, doesn't it!) You've nearly discovered 'tritone substitution'.

Laurence
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  • Laurence this is beatifuly explained! I wander why aug6 is named the way it is iff it is aug7 without the E note... – LoveIsHere Dec 22 '17 at 06:57