Diatonic Theory - The Four-Note Chords

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Let's take things one step further...let's build the chords of a Key to the "7" type chord out of a 
key...these will be 4 note chords as opposed to the three note triads we looked at before. They will be 
built with the 1, 3, 5, and 7 notes of each modes. This is where the true harmonies of the modes/keys 
really lie...in the key of C again:

Imaj7 = Cmaj7
iim7 = Dm7
iiim7 = Em7
IVmaj7 = Fmaj7
V7 = G7
vim7 = Am7
viim7b5 = Bm7b5

Ok, can you see I double up the lower case minor lettering and still stated the "m" after it. This could be 
written without the "m", such as ii7 and it would still be a m7. Or it could also be, and is very commonly 
written as, IIm7...upper case II being the second note/interval of the scale and the m7 signifying the 
"minor 7". There's really a number of ways this can be written so it's worth understanding as you will run 
into it based on however the person who wrote the chart presents it, and it will be something you pickup by 
looking at other Mode and Key resources/material.

So, those chords could be written as:

Imaj7 = Cmaj7
ii7 = Dm7
iii7 = Em7
IVmaj7 = Fmaj7
V7 = G7
vi7 = Am7
vii7b5 = Bm7b5

Or, they could be written as:

Imaj7 = Cmaj7
iim7 = Dm7
iiim7 = Em7
IVmaj7 = Fmaj7
V7 = G7
vim7 = Am7
viim7b5 = Bm7b5

Or, they could be written as:

Imaj7 = Cmaj7
IIm7 = Dm7
IIIm7 = Em7
IVmaj7 = Fmaj7
V7 = G7
VIm7 = Am7
VIIm7b5 = Bm7b5

Hopefully that all makes sense.

And, now we also know the "7" type chords of a Key also. And this will also be static/constant/consistent 
between Keys.

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