And let us recall The Ventures "Walk, Don't Run" of Am, G, F, E7 fame.

Now that's interesting - I can hear it in my head as I type.

In making music it should be enough for you to like the sounds you make. The rules only ever come after music has been played. They are an attempt to explain what has happened and should not be seen as a 'How to do it' manual.

I'm sure it was meant well, but this kind of comment drives me up the wall. As far as I can see, once you know the rules, you can break them - and the better you know them, the better you can break them. If you don't know the rules, all you can do is plonk your fingers down at random and hope you get a nice sound out - and usually you won't.

Take the sus4 chord - I saw that in the notation of a song I was looking at and had no idea what it was, so I googled it; now I'm using it a lot. I might have blundered into the discovery that D, G and A sound interesting together, but without knowing what I was playing that would just have been a random fact to file away. Admittedly, some people do learn instruments by discovering odd combinations of notes and having their fingers learn every single one, but I really haven't got the time it would require (either hours in the day or years ahead of me!).

Codger: Note also that, in the natural minor, the diminished triad occurs on the II chord rather than the VII chord, and as the II chord is rather prominent in harmony (in the sequence of fifths, and thus in many progressions, it immediately precedes the V chord)

Let me see if I've got this.

Chords in the major scale, key of C:

C: C, E, G (I)
Dmin: D, F, A (ii)
Emin: E, G, B (iii)
F: F, A, C (IV)
G: G, B, D (V)
Amin: A, C, E (vi)
Bdim: B, D, F (vii-wivva-degree-symbol)

Chords in the natural minor, key of A minor:

Amin: A, C, E (i)
Bdim: B, D, F (ii-wivva-degree-symbol)
C: C, E, G (III)
Dmin: D, F, A (iv)
Emin: E, G, B (v)
F: F, A, C (VI)
G: G, B, D (VII)

The harmonic minor also gives you the option of

E: E, G#, B (V)

and presumably

G#dim: G#, B, D (vii-wivva-degree-symbol)

although thinking about sharped keys makes my head hurt.

Sequence of fifths (I know I could google this, but let me try it in caveman-with-a-calculator mode):

Assume key of Cmaj. Then:

C -> G -> D -> hey, I know this one -> And -> Ends -> Battle. Get F in there somewhere. So...

IV -> I -> V -> II -> VI -> III -> VII... is that right? Doesn't look right. Try it descending? Also check those minors.

I -> IV -> vii dim -> iii -> vi -> ii -> V -> I

Presumably different progressions would be used in minor keys. But if you used this one you'd get

i -> iv -> VII -> III -> VI -> ii dim -> v/V -> i

Which in this case would be

Amin -> Dmin -> G -> C -> F -> Bdim -> Emin/E -> Amin

Which isn't quite the progression I started with, but it's close enough - it's got the G, the F and the E, most importantly!