Lets first get this out of the way. In a major progression the I, IV & V chords are the structure chords the ii, iii & vi are the minor chords and they add color and or flavor. The vii is the diminished chord and it has several functions. In a minor progression the minor chords are your structure chords and the major chords are you color or flavor chords. That's kinda important.
The V or V7 being the climax chord is my name for it. The V is the dominant chord and the dominant chord wants to move to the tonic I chord. When you add the b7 and make the dominant chord a V7 that increases the tension of the chord and it wants to resolve to the I tonic chord RIGHT NOW. If you went somewhere else that would sound anti-climatic - thus I call it the climax chord. You have reached the climax of the progression so it is time to end by resolving to the tonic I chord.
Verse structure; The first two lines normally bring up a subject. The 3rd and 4th line react to what was said in the first two lines - a four line verse brings up a subject then the last two lines react to what was said in the first two lines, thus each two line segment stands on it's own, therefore each has a complete V-I progression. Normally. In art and music there is always exceptions.
Here is something that may help. Each chord has a function
it likes to preform.
- The I chord is the tonic tonal center of the progression. The I chord can move anywhere it wants to in the progression, however, when you move to the I chord you lose any tension you have built up and you are now back at rest. If you want to go further you have to start building tension over again.
- The ii chord is a minor sub-dominant (some say pre-dominant) chord which likes to move to a dominant chord.
- The iii chord is a minor mediant chord, i.e. middle chord, it likes to move somewhere. In this move it likes to drag the vi chord along with it.
- The IV is a major sub-dominant chord which likes to move to a dominant chord. Notice the ii and IV both like to move to a dominant chord. Because they both like to move to the same chord they can sub for each other.
- The V is the dominant chord which likes to move to the tonic I chord. Adding the b7 for a V7 chord increases the tension and the V7 chord wants to resolve (move back) to the I chord as soon as possible.
- The vi is a minor (relative minor) chord and it likes to move to a sub-dominant chord.
- The vii is the diminished chord. It is also a dominant chord like the V, however, it is in no hurry to resolve to the I chord and is often used as the beginning of a turn-a-round. For example vii-iii-vi-ii-V7-I. So if you want to resolve to the tonic I chord use the V or V7. If you want to move somewhere else use the vii. The vii is known as the leading tone diminished chord, i.e. it can be used to lead somewhere else.
- This all comes from www.musictheory.net. Lessons/common chord progressions. Go to the site they have a step by step graph of how a common chord progression moves. Worth your time.
Now that is what chords
like to do. All chords in a key will sound OK with every other chord in that same key, so yes other chords can move to the I chord.
You can make them move as you see fit. If we let them move as they like, good things normally happen.
Chords do two things. 1) provide movement within the verse and 2) harmonize the melody line by sharing like notes, i.e. the treble clef and bass clef share some notes. How many? One per measure gets harmony. Two is better, is three necessary? It's like gravy, if you like gravy spoon it on. So it's a balancing act. Chords are placed so they provide movement and harmony. Normally I leave this task to the songwriter and play the chord he chose to use, i.e. I find a chord chart and play from that. But, it does help to understand what is going on.
For this to sink in I'd suggest you call up some chord charts on your songs and study the progressions. Ask yourself why are they moving as they are? A basic dirt simple movement would be Rest, Tension, Climax and then resolution and return to Rest. Think of it this way; the song writer has the verse start off at rest, that's boring so he/she adds some tension and then works toward a climax. Once you have reached climax it's time to end this verse so verse number two can bring up another thought. I think you will find that most four line verses will have one V-I progressions in the first two lines and then repeat this V-I cadence in the 3rd and 4th line. Verse two starts the process over again.
I hope that answered your question, if I confused, that was not my intent. Ask again...