There are so many songs out there that go G C D Em or D G A Bm and so on. At first, it might just seem like this is because the writers are unimaginative. But a closer look reveals that there is actually good reason behind it. And that's what we're gonna look at today.
Let's Start At The Beginning.
G, C, D, and Em. These are all chords in the key of G. They are the 1-4-5-6m chords. Now why do I call it that? Because if you look in a G scale, those chords are the 1st, 4th, 5th, and 6th notes in a G scale. Let's take a look at that:
1 2 3 4 5 6 7 O
G A B C D E F G
Now why is it these chords are used? The 4, 5, and 6m chords all have at least one note in common with the 1 chord. Let's take a look at that:
G Chord: G B D
C Chord: C E G
D Chord: D F# A
Em Chord: E G B
The reason its the 6m instead of the 6th major, is because the 6m is the relative minor of the 1, which means the scale has the same notes.
G scale: G A B C D E F#
Em scale: E F# G A B C D
Let's Check All That Out In Another Key.
1 2 3 4 5 6 7
C D E F G A B
C Chord: C E G
F Chord: F A c
G Chord: G B D
Am Chord:A C E
C scale: C D E F G A B
Am scale: A B C D E F G
Pretty cool, huh? And then, if it sounds good, most guitarists will add in 7ths and things of that nature. I hope this helped!
the next thing that bothers me is that you aren't using roman numerals, typically that is what is used when refeering to a chord progression, upper case for major lower case for minor, so it would read I IV V vi. (this might just be a pet peeve of mine but I find using roman numerals kind of cleans it up a bit)
finally the resoning for the vi being minor is sound, I guess, but really all you have to say is that it is diatonic to the scale, not because its the relative minor. if you don't know the word diatonic, it means that only notes from the scale can be used, or the chord uses no accidentals.
so for the key of G major you would have:
I G major - G B D
ii A minor - A C E
iiiB minor - B D F#
IV C major - C E G
V D major - D F# A
vi E minor - E G B
vii° F# diminished - F# A C
note that all the chords only use a combination of three of the fallowing notes G A B C D E F#
I'm not trying to make you look dumb but where did you get your information? I mean if all you are looking for is at least one note in common with the root chord then wouldn't the iii be a prefeered note, seeing as it has 2 notes in common? and with that in mind wouldn't it make sense that I iii vi I would be the strongest chord progression?