# Quick question regarding diatonic triads...again

Discussion in 'General Instruction [BG]' started by Fassa Albrecht, Jan 24, 2012.

1. ### Fassa Albrecht

Feb 18, 2007
Tyneside, UK
I'm failing to understand why this is so difficult for me to understand when I play two other instruments where I have little trouble with chordal theory.

The question I have is this: in my jazz book there are two examples of the diatonic major scale. One is in the key of C, the other G. Now these both have within them the chord of D, in the case of the C scale, it's ii, the G scale, it's on the V.

My problem comes because from my understanding of chord theory, the D chord has the flatted third with the F, making it minor. So how in the key of G can this chord suddenly be major without there being an F# in it?

And why does the F#diminished chord in the key of G get written with a F as the starting point in standard notation when it's based on the vii dim which in this case is a sharped note.

The more I read, the more I get confused.

2. ### PacmanLayin' Down TimeStaff MemberGold Supporting Member

Apr 1, 2000
Endorsing Artist: Roscoe Guitars, DR Strings, Aguilar Amplification
The key signature?

Take a piece of staff paper, write the key signature that you'd like to study.
Next, write the major scale for that key (since you've written the key signature, you shouldn't need accidentals).
Now, stack thirds on each note of the scale you've written. (again - since you've written the key signature, you won't need accidentals) Do this twice, so you now have the major scale harmonized in triads.

3. ### MalcolmAmos

Yes, IMO the only way you will understand this is to understand how stacking 3rds puts the correct 3's and 7's in the chords, i.e. the minor chords get the b3, and the correct 7 or b7 go where they should - every time.

Maj7 have a 3 and a 7.
Minor chords have a b3 and a b7.
Dominant seven chords have a 3 and a b7.
Diminished chords being both minor and diminished have the b3 and b7 with a b5.
There will always be three major chords, three minor chords and one diminished chord in a key made from seven scale notes.

Here is C, use that as your Rosetta stone, and then you do G.

Code:
```C Major scale &#8211; notes and chords
Note	 ScaleTone 	Chord	spelling	        function
C		1	Cmaj 7	CEGB R-3-5-7 		I	(tonic)
D		2	Dmin 7	DFAC R-b3-5-b7		ii
E		3	Emin 7	EGBD R-b3-5-b7		iii
F		4	Fmaj 7	FACE R-3-5-7		IV	(subdominant)
G		5	G7	GBDF R-3-5-b7		V	(dominant)
A		6	Amin 7	ACEG R-b3-5-b7		iv
B		7	Bmin7b5	BDFA R-b3-b5-b7		viidim  (diminished ```
How did that b3 get into the D chord? Your stack has D-F-A-C. What notes are in the D major scale? Yep, D-E-F#-G-A-B-C#. So your stack had to flat the F# and the C# thus anytime you have a flatted 3rd (b3) you have a minor chord and that b7 with a minor chord is a minor seventh chord. If the b7 had been with a major chord it would be a dominant seventh chord, i.e. G7.

Make the key of G - that fish thing.

Good luck.

4. ### PacmanLayin' Down TimeStaff MemberGold Supporting Member

Apr 1, 2000
Endorsing Artist: Roscoe Guitars, DR Strings, Aguilar Amplification
Malcom, the vii chord in a major tonality is not diminished. It's a Min7b5. Diminished chords are formed by stacking minor 3rds (1-b3-b5-bb7).

5. ### Fergie Fulton

Nov 22, 2008
Braintree
Retrovibe Artist rota
Hi Jon, i was taught to consider a Half Diminished Chord as Min7b5, is this wrong or is the term half diminished just not used any more?
It was called half diminished because the 7th has a single b rather than a double bb, so it was said to be ' half. '

I still use it under the banner of Diminished Cords because it is easier to deal with it in this context, or is there an easier way to deal with it say with in a Jazz context?

thanks.

6. ### MalcolmAmos

You are correct the R-b3-b5-b7 is the 1/2 diminished or min7b5 as you say. Little circle with a strike through.

As Fergie indicated to keep the ole rule of three major, three minor and one diminished I should have indicated it being a 1/2 diminished chord.

7. ### blakelock

Dec 16, 2009
...
i think you're all correct and the OP should go through those exercises but there is a mistake in the OP. he/she says

oh, but there IS an F# in it. the F# is the 7th of the G major scale and acts as the major 3rd in the D chord.

next...
sharps and flats are only indicated at the beginning of the music through the key signature. the key sig tells you that every F in the music will actually be an F#...unless otherwise noted.

8. ### younggun

Jul 19, 2008
San Antonio
Yep, that's it. I spotted that when I first read the OP's post too. Seems like its just a simple error in understanding the key signature that caused the confusion.

Not to derail the thread, but I was once very confused about the 1/2 diminished and diminished triad myself...until my teacher explained to me that the diminished triad is NOT based on a diatonic scale. Its based on the, well, diminished scale (a symmetrical scale base on half-step whole-steps creating a 9 note scale, not 8 as the diatonic scales are). In a way you have to think of the diminished triad as a whole other animal, and not try to fit it into the diatonic scale. The term half-diminished can be a bit misleading, and it's probably less confusing to just to say minor 7, flat 5.

9. ### PacmanLayin' Down TimeStaff MemberGold Supporting Member

Apr 1, 2000
Endorsing Artist: Roscoe Guitars, DR Strings, Aguilar Amplification

Which is why I said:

I know people still use half-diminished interchangeably with M7b5.

99% of the times you see it, it's functioning as a ii in a minor key, so I address it accordingly.... What do your ears tell you?

10. ### shwashwa

Aug 30, 2003
NJ
incorrect. the diminished TRIAD is built on the 7th degree of the major scale. it is diatonic. the triad built on the 7th degree of the major scale is not half diminished nor is it minor 7 flat 5. it is a diminished traid. if we're talking about 7th chords then what you say is correct

shalt thou count to three, no more, no less. Three shall be the number thou shalt count, and the number of the counting shall be three. Four shalt thou not count, neither count thou two, excepting that thou then proceed to three. Five is right out.

11. ### Stick_PlayerBanned

Nov 13, 2009
Somewhere on the Alaska Panhandle (Juneau)
Endorser: Plants vs. Zombies Pea Shooters
First there is NO half-diminished triad (three-notes). The "half-diminished" label is only applied to a Seventh Chord (four-notes).

Example:

A, C, Eb = Diminished Triad - A[SUP]o[/SUP]
A, C, Eb, G = Half-Diminished Seventh Chord - a Diminished Triad plus a Minor Seventh - A[SUP]ø[/SUP]7.
A, C, Eb, Gb = Full-Diminished Seventh Chord - a Diminished Triad plus a Diminished Seventh - A[SUP]o[/SUP]7

The Diminished Triad is a Diatonic Chord. The above example (A[SUP]o[/SUP]) is a Diatonic Triad from the Key of Bb Major, as well as the above example Half-Diminished Seventh Chord, A[SUP]ø[/SUP]7.

The Full-Diminished Seventh Chord, A[SUP]o[/SUP]7 from the above example, is the diatonic vii[SUP]o[/SUP]7 chord from the Key of Bb Minor.

The scale that you refer to (half-step/whole-step), is a synthetic scale. Bach and Mozart were NOT using these types of scales to derive harmony from.

12. ### FretlessMainly

Nov 17, 2010
I would say this differently. While you do often see:

| Dmin7(b5) | G7(b9) | Cmin | in the key of c minor, I think another usage is just as common:

| Dmin7(b5) G7(b9) | Cmin7 | F7 | BbMAJ7 |

So, the min7(b5) chord functions as a ii chord of the II chord (in this case, Bb Major). The ii v of Cmin often functions in c harmonic minor, but when you get to the Cmin7, you modulate to Bb Major.

13. ### PacmanLayin' Down TimeStaff MemberGold Supporting Member

Apr 1, 2000
Endorsing Artist: Roscoe Guitars, DR Strings, Aguilar Amplification

C harmonic minor in this case could be non-diatonic to the ii-V-I in Bb. I think, ears being the deciding factor of course, I'd probably still approach that as a ii-V in C minor. And somewhere in that bar of Cm work towards the Bb major resolution.

14. ### FretlessMainly

Nov 17, 2010
Yes, I realize that, but the Ab from the D-7(b5) and the B natural in the G7(b9) just scream C harmonic minor. Using a ii v of C minor is still an option, of course. That's the beauty of jazz - there are often several options. One keeps the basic Bb tonality through the entire phrase and the other offers more tonal variety through the phrase.

15. ### Otso

Mar 6, 2006
Finland
When I first read jazz theory I was a bit confused, having learned about tonality mostly through classical music theory, where a half-diminished chord usually is the VII degree in major tonality and often interpreted as a V9 chord without the root (it has the important leading tone for the tonic and the characteristic interval of a diminished fifth, therefore functioning as a dominant for the tonic). Musical context changes things a lot.

16. ### BassyBillThe smooth moderator...Gold Supporting Member

Mar 12, 2005
West Midlands UK
Excellent stuff.