vii - Dim7

Please forgive my poor (yet improving) knowledge of theory but can anybody briefly explain why the 7th (vii) degree in a major key is always diminished? - I,ii,iii,IV,V,vi,vii0 -

its just in the way the scale is and how it fits

I-ionian-major
ii-dorian-minor
iii-phrygian-minor
IV-lydian-major
V-mixolydian-major
iv-aeolian-minor
vii0-locrian-diminished

its just the way its placed diatonicly. diatoniclly it has to be diminished. maybe someone can explain it better.

No that helps a little bit. Im certain that theoretically there is a reason for it, it's just not entirely clear at the moment. I know that it has to fit into the scale i just don't quite see at what point. For example in the key of C major you have:

C - Dm -Em - F - G - Am - Bdim

It makes sense that the Bdim triad is all with in the C major scale

Bdim = B, D, and F

But again why diminished? Sorry if im dumb and completely missing the point. And also im not a huge fan of the diminished chord.

really because the 7th chord only fits diatonicly diminished

play the chords on the scale, the diminished has to be flat 3rd flat 5th bc of the fact if it wasnt it wouldnt fit in the scale.

Oh OK i see what your saying!!! Because if i were to play for instance Bmaj which consists of B, F#, and D# it wouldnt fit because those notes are not in the scale.... Hence the flat 3rd and 5th (D and F). Nevermind it makes sense now, just didn't look into it far enough.

Thanks EMB5490

In key of "C" Diatonic major scale(parent mother scale/Mother major scale/whatever you call it)

Ionian- C(1) D(2) E(3) F(4) G(5) A(6) B(7)
Dorian- D(1) E(2) F(b3) G(4) A(5) B(6) C(b7)
Phrygian- E(1) F(b2) G(b3) A(4) B(5) C(b6) D(b7)
Lydian- F(1) G(2) A(3) B(#4) C(5) D(6) E(7)
Mixolydian- G(1) A(2) B(3) C(4) D(5) E(6) F(b7)
Aeolian- A(1) B(2) C(b3) D(4) E(5) F(b6) G(b7)
Locrian- B(1) C(b2) D(B3) E(4) F(b5) G(b6) A(b7)

or as i like it (don't know if your more a letter or number guy)

Ionian-1-2-3-4-5-6-7
Dorian-1-2-b3-4-5-6-b7
Phrygian-1-b2-b3-4-5-b6-b7
Lydian-1-2-3-#4-5-6-7
Mixolydian-1-2-3-4-5-6-b7
Aeolian-1-2-b3-4-5-b6-b7
Locrian-1-b2-b3-4-b5-b6-b7

Now we need to learn the interval of our four triads(chords with three different frequencies in them). But first western harmony is built around thirds so each chord is just thirds stacked on top of one other.
Major triad-- 1,3,5 or major 3rd to a minor 3rd
Minor triad-- 1,b3,5 or minor 3rd to a major 3rd
Augmented triad-- 1,3,#5 or Major 3rd to a major 3rd
Diminished triad-- 1,b3,b5 or minor 3rd to a minor 3rd

Ok now on to the basic rule of modes(which some people skip) which is intervals. Some people see that C Ionian(commonly referred to as major scale) and A Aeolian(commonly referred to as minor scale) have the same notes so they are the same scale. NOOOOOOOOOO WRONG!!!! C Ionian is 1-2-3-4-5-6-7 while A Aeolian is 1-2-b3-4-5-b6-b7 the key is all in the intervals or as Carl(i think) called is constructive math(i liked that term).

so now your probably wondering why all this bumbling on modes. well, all diatonic basically means is shared notes. and the modes are scales which share the same notes. and from these scales, which share he same notes, we get one of the many ways to develop chords, progress and other musical things.

so now on to diatonic progressions. when you see a progression, example I IV V, that can mean many things. they don't have to fit into a diatonic progression as you may or may not know. Like the 12 bar blues which will have each chord be a dominant. But as you stated.............................................................

well now your talking about a diatonic progression. A progression that is based off of the modes of a Diatonic scale(there is five different "proper" scales, one being harmonic minor) notably the diatonic major scale(or other names stated above). So what we do is fit the triad into each scale. for examples, The Ionian scale has a one, three, and five as intervals and that makes a major triad. so the first "degree" is a Major triad or symbolized as "I", or the Aeolian scale has a one, Flat Three, and Five as intervals making the Sixth "degree" a minor triad or Symbolized as "vi". So when we get to the "7th (vii) degree" we base it off of the Locrian scale. which has One, flat Three, and a flat five as intervals, making a diminished triad.

also the "vii" is not a Diminished 7th(1,b3,b5,bb7[6]) it is a half-diminished 7th(1,b3,b5,b7). the Diminished 7th is note native to the major scale. as stated above a what makes a Diminished chord is minor thirds stacked up one other. while a half-diminished 7th(1,b3,b5,b7) is a minor 3rd, to a minor 3rd, to a major 3rd. making it "half" so to speak. while a Diminished 7th(1,b3,b5,bb7[6]) is just made of minor thirds, and that doesn't happen in the diatonic major scale.



well if you continue in you music you will be the diminished chord is used every where. just pick up a fake book you will see it all over the place(a 7b9 is a diminished chord you may see that more but it is the same thing, well... I'm not going to explain it hear but there different and the same at the same time)

edit- well that sucks, and it deleted my spacing in the charts i had it all lined up

Ok ive got a good glimpse of the big picture. Thats alot of information so im gonna have to read that 30 times but is a very thorough explination. I hope this makes sense, so as im playing through a diatonic progression, i am not simply playing the C major scale. Each chord in the order of I,ii,iii,IV,V,vi,vii0 each chord is associated with the relative mode.
I - ionian
ii - Dorian
iii- Phrygian
IV - Lydian
V - Mixolydian
vi - Aeolian
vii0 - Locrian

So the 7th degree is diminished because in the relative (locrian) mode the 3rd and 5th are flat making it a diminished trid.....? Right? It seems as though i just repeated what you said but i put into my own words that i understand so is that correct?

yes your correct.
but as i tried to point and and will state again this is just one way of looking at things. music is largely perspective based and will change depending on where you "stand". So don't take this and say this is how chords are made or this is how such and such is done. Because as pointed out before if taking into blues(or many other things) your going to be lost.

Haha good point! I think thats why they call it "Theory".

If you want a quick rundown on this kind of stuff, I have a lesson on chord building and triads on here. You should give that a quick read.

Building Chords: Major, Minor, Diminished, and Augmented

So you don't have to go hunting.