Dominant 7 chord built on b7

[Jimmy_Jimmy]

Hello,

Was just browsing through a book of jazz standards today, can't remember which song it was but i noticed the chord progression went from a Maj7 chord to a Dom7 chord a tone below (i think it was Fmaj7 - Eb7).

Now i understand that it's possible that this sequence was used to change key but wondered if there's another explanation,ie is this a common jazz change ? Does it suggest a certain scale ? Is it maybe a case of 'modal interchange ?

thanks in advance for any opinions or explanations - Jimmy

[crusty]

A dominant 7th chord is closely related to three other dominat 7th chords. The one a tritone away, the one a minor third up and the one a minor third down. In the key of F the dominant 7th would be C7. Up a minor third is Eb7.

[Jimmy_Jimmy]

Thanks for your post crusty.

So in examining this change (Fmaj7 - Eb7) could a possible explanation be that the overall key may well be D minor, with Eb7 being the tritone sub for its V chord (A7) and the Fmaj7 simply being the III Maj7 chord ?

[crusty]

Thanks for your post crusty.

So in examining this change (Fmaj7 - Eb7) could a possible explanation be that the overall key may well be D minor, with Eb7 being the tritone sub for its V chord (A7) and the Fmaj7 simply being the III Maj7 chord ?

Sounds good to me. Could be overall D minor, or just temporary.

[JonR]

It really depends what chord comes after the Eb7...!

If it's Dm, then yes, the Eb7 is (arguably) acting as a tritone sub for A7.

BTW, it's quite common to use a bVII7 to resolve to I. So you can find Eb7-Fmaj7 in a lot of jazz standards (in key of F).

[Asperjames]

JonR, how exactly does tritone substitution work? and is it different from secondary dominants?

say i'm playing a i-IV-V7-i in am. if secondary dominants were added to each chord it would be...

d7 - am7 - a7 - dm7 - a7 - e7 - d7 - am7

[JonR]

JonR, how exactly does tritone substitution work? and is it different from secondary dominants?

say i'm playing a i-IV-V7-i in am. if secondary dominants were added to each chord it would be...

d7 - am7 - a7 - dm7 - a7 - e7 - d7 - am7Um, nope. Firstly the dominant of Am is E7, and (in that key) it's not secondary.
A secondary dominant is the V of any chord other than I.

If you were to precede each chord in that sequence with its dominant, it would be:

E7-Am | A7-Dm | B7-E7 | E7-Am.

A7 (V of iv) and B7 (V of V) are the secondary dominants.

A tritone substitute is a chord whose root is a tritone away - and it almost always means switching one dom7 for another.
Replacing the secondary dominants with their tritone subs, therefore, gives:
E7-Am | Eb7-Dm | F7-E7 | E7-Am.

You could also replace the main dominant (E7) with its tritone sub (Bb7).

Tritone subs work (partly) because they share the same inner tritone between 3rd and 7th, which is the "active" interval in the chord.
A7 has C#-G (3-7), and Eb7 has Db-G (7-3).
B7 had D#-A, F7 has Eb-A.

The other way they work (which is neat) is the root and 5th make a semitone descent to the next chord. If the tritone sub is preceded by the ii of the tonic, you get a double semitone fall. E.g., Dm7-Db7-C (instead of Dm7-G7-C).

Tritone subs share the same improvisation scale.
E7 (in key of A minor at least) would probably take the E altered scale, which is the 7th mode of F melodic minor. (E-F-G-Ab(G#)-A#-C-D)
Bb7 (if resolving to Am or Amaj) would take the Bb lydian dominant scale, which is the 4th mode of - F melodic minor! (Bb-C-D-E-F-G-Ab) (Neat, huh?)

Lydian dominant is confirmed if you see a 7#11.

To get us back on topic - :smile: - bVII chords also usually take the lydian dominant scale. Bb7 might easily appear as the bVII in the key of C major, where it would also use the F melodic minor scale.

JonR

[pml]

A secondary dominant is the V of any chord other than I.You mean, the V of any diatonic chord other than I, correct? Other dominant chords would be called auxiliary dominants.

PML

[JonR]

Yes - well caught!

[crusty]

You mean, the V of any diatonic chord other than I, correct? Other dominant chords would be called auxiliary dominants.

PML

(Whispers) pssst! JonR, I think pml could become a powerful ally, we need to seduce him to the dark side! :_devil:

[pml]

I think pml could become a powerful ally, we need to seduce him to the dark side! :_devil:What, me worry? :roll:

PML

[CaptainSG]

uhhh....this is weird to me...perhaps I'm missing common knowledge in theory but when you guys talk about dominant chords, that only one I know that comes diatonically is the V....and then, when you guys bring up the tri-tone chords, I get confused as I don't know where the minor third is when going down....going up I know....but maybe i just screwed up something...

[pml]

when you guys talk about dominant chords, that only one I know that comes diatonically is the V....A "dominant chord" is actually any chord that has at least, apart from the first, a major third and a minor seventh. Instead of the major third, you can also have a perfect fourth, making it a suspended dominant chord, but ignore this information for the moment if it becomes too confusing.

On the other hand, it's possible to use non-diatonic chords within a progression without compromising the sense of key in the progression. They are then called Modal Borrowing Chords (MBC). Note that a MBC can eventually have its root on a diatonic degree, but it's never a diatonic chord.

Back to dominant chords. When the dominant chord is the V7 of the I degree, it's called the primary dominant (duh). When it's the V7 of any diatonic degree other than the I, it's called a secondary dominant. In any other case, i.e. when it's the V7 of a non-diatonic degree, it's called an auxiliary dominant.

Examples:

Primary dominants:

V7 Imaj7
|| G7 | Cmaj7 ||

V7 Im7
|| G7 | Cm7 ||


Secondary dominants:

Imaj7 V7/III IIIm V7/II IIm7 V7/V V7 Imaj7
|| Cmaj7 | B7 | Em | A7 | Dm7 | D7 | G7 | Cmaj7 ||


Auxiliary dominants:

MBC MBC
Imaj7 V7/bIII bIIImaj7 V7/bVI bVImaj7 IIm V7 Imaj7
|| Cmaj7 | Bb7 | Ebmaj7 | Eb7 | Abmaj7 | Dm | G7 | Cmaj7 ||

The "V7/whatever" notation means simply that it is the V7 of the "whatever" degree.

In the last two examples, you can see the secondary and auxiliary dominants being used to prepare the following chord. In the case of the secondary dominants, they're preparing a diatonic chord, and in the case of the auxiliary dominants, they're preparing a non-diatonic chord. This is a common use for them.

when you guys bring up the tri-tone chords, I get confused as I don't know where the minor third is when going down....going up I know....but maybe i just screwed up something...Err... I don't know what minor third you're talking about, maybe I've just missed something in the thread? Or are you confusing a tritone with a b3? If so, a tritone is six halfsteps (or semitones), which makes it a #4 or a b5, and divides the octave exactly in half, so its inversion is also a tritone. Anyway...

Tritone substitution is when you replace a dominant chord with the other dominant chord that shares the same tritone. In the key of C, the V7 is a G7, which spells G-B-D-F. The tritone is formed between the third and the seventh of the dominant chord. For G7, this will be B-F, then. As the tritone is symmetrical, we can see it as F-B and still have a tritone. The dominant chord that has F as its third and B (or more correctly, its enharmonic Cb) as its seventh is Db7, which spells Db-F-Ab-Cb, so Db7 would be the tritone substitution chord for G7.

In practice, I doubt anyone will go through all this reasoning to find a subV7. You can just form a seventh chord whose root is a #4 below or a b5 above the root of the dominant chord you want to replace. Or you can form the dominant chord whose root is a b2 above the root of the resolution chord.

One of the sweet things about the subV7 is the chromatic movement of the root in the common II-V-I progression. Compare these:


IIm7 V7 Imaj7
| Dm7 | G7 | Cmaj7 |

IIm7 subV7 Imaj7
| Dm7 | Db7 | Cmaj7 |


I just hope all this doesn't confuse you further... :(

PML