PaperDog wrote:All this talk about chords... May as well be talking about a map... 
If 'E' is Grand Central Station, then when we round a corner, and go up some stairs, through a door, into an elevator, and back down to the underground tunnel... Then...when we get there...what chord would that be?
If we want to head north from E, but want to stop for coffee just up the street... what chord would that be?
If during our traverse, we see a broken fire hydrant spraying water and we want to get sprayed. When we reach it...what chord would it be?.
Each artist will give you a different answer, respectively. However, one thing is consistent, The variations on each root/dominant reference (note) in conjunction with the variation of musical gesture (ie rythms, meters) will tell the listener a reasonably vivid story.
We say there are rules about musical sequence per se...That is , there are rules that define the scales. I say hogwash...The definition is an attempt to express what really prevails, which is the need for sustainable, musical continuity,. That is is why scales exists ad are referenced. Each position is identifiable and can thus be exploited.
Therefore, When we speak of chords, we speak of lil red flags in a map-quest called a song. When I Write.. I always suffer the same barrage of questions..."Where am I?, where am I headed"

well, i lived in NYC for 22 yrs and never not once thought of Grand Central Station as being in the key of "E".
been playing a lot longer than that and never thought of the key of "E" as Grand Central Station!
obviously different musicians look at things differently , hear things differently, and communicate differently.
but for the sake of clarity and quick effective communication...if i'm sitting in w some folks on stage playing a song i've never heard before..for ME it's so much easier if the person whispering the upcoming chords say's "ok, back to the "E" here" if they said "go to Grand Central Station" well, that wouldn't be quite as helpful.
as for "rules" of course music has rules...what doesn't? anyone is free to follow them or ignore to whatever extent they choose.
as for maps.....they are helpful and useful tools. and they're quite useful in music too. if you hire me to play a session... if i know the form of the song (the map) i'm not gonna be wasting a lot of time going to the chorus when you're playing the next verse.
if you get up and sit in with a band playing some tune....if you don't know the "map" you're gonna end up in the wrong zip code!