1. Let’s say I’m in G and want to switch keys, are there some keys that would sound better when switching, or can I switch to whatever key I want.

2. Dm7-G7-CM7 is a ii-V-I in the key of C, but those aren’t the only chords you can play on those notes. If I played Dm6-G9-Csus4, would that still be a ii-V-I?

3. Most people play the VI chord as a dominant chord most of the time. If you’re in C and you play the VI chord as A7, does that mean you’ve temporarily changed to the key of E?

4. I know a lot of common chord progressions, but songs don’t go ii-V-I-ii-V-I-ii…or I-VI-ii-V-I-VI-ii-V… all the way through. Where do you go after the end of the progression?

1. Let’s say I’m in G and want to switch keys, are there some keys that would sound better when switching, or can I switch to whatever key I want.

There's lots of ways to do it, and they have different uses. Abrupt modulations are the norm in pop music, where you might bump the key up a semitone for cheesy dramatic effect.

2. Dm7-G7-CM7 is a ii-V-I in the key of C, but those aren’t the only chords you can play on those notes. If I played Dm6-G9-Csus4, would that still be a ii-V-I?

Yep, but that particular example would be weak because of the suspension.

3. Most people play the VI chord as a dominant chord most of the time. If you’re in C and you play the VI chord as A7, does that mean you’ve temporarily changed to the key of E?

That's normally called a secondary dominant. It gives a stronger resolution to its tonic than using the minor version. You're still in the same key.

4. I know a lot of common chord progressions, but songs don’t go ii-V-I-ii-V-I-ii…or I-VI-ii-V-I-VI-ii-V… all the way through. Where do you go after the end of the progression?

The reason there is such an emphasis on things like the ii-V-I progression is that it's a common feature in a whole lot of tunes. It's a standard way to resolve a musical phrase. Check through a fake book of standards and look for them.

Abrupt semitone key changes (going from C to C#) is called a "producer's key change" and it's used to give the song artificial hype when it starts to get boring. It's called a producer's key change because the songwriter probably didn't put it in because there's no real musical bridge between the two (except when there is, like in Soul Man where the bridge hides the key change).

As dlloyd said, V-I is a very common way to resolve a song. The V creates tension, going to the I resolves it.

The V creates tension for several reasons. One, if you harp on it (just the note not the chord) long enough, you want to resolve to I naturally. Two, the V chord contains the leading tone of I. V contains as lot of the same notes as a I7 (or Imaj7) chord, which is one more reason it wants to resolve to a I chord.

ii is "the five of the five." It's a way to extend the V-I resolution even further.

If you want to experiment with these things, grab a guitar and play them. Play a V7 chord 4 times in a row and then go to a I chord and just see how it sounds. Play a ii7 chord four times then go to a V chord and see how it sounds, etc. Play a I7 or a Imaj7 chord four times and then play a I chord and see how it sounds.

Probably the best way to learn is to learn as many songs as possible and pick out the chord progressions & reasons for them. One day I'll create a catalog of popular songs with certain kinds of chord progressions for practice & as teaching material...

I found a copy of Autumn Leaves that my bass teacher gave me. It's in the key of G and the chord progression goes
A-7 D7 GMaj7 CMaj7 F#-7b5 B7 E-

Obviously the first five chords are the ii-V-I-IV-viidim, and the E- is VI, but what about the B7? Is it a secondary dom., chord substitution?

Then later in the song they play that progression again followed by Eb7 D-7 and Eb7. What's happening there?

I found a copy of Autumn Leaves that my bass teacher gave me. It's in the key of G

It's actually E minor, but you can think of the first part as a major ii-V-I, as you've worked out for yourself...

and the chord progression goes
A-7 D7 GMaj7 CMaj7 F#-7b5 B7 E-

Obviously the first five chords are the ii-V-I-IV-viidim, and the E- is VI, but what about the B7? Is it a secondary dom., chord substitution?

The F#m7b5 B7 Em bit is a minor ii-V-i

Harmonising the natural minor scale, you'd expect the progression to go F#m7b5 Bm7 Em, but that leads to weak resolution to the Em chord.

In major harmony, what makes the V-I cadence particularly strong is the combination of the movement of the dominant (root of the V chord) to the tonic, plus the half-step movement between the leading note (major third of the V, seventh degree of the scale) to the tonic.

When harmonising the minor scale, we often raise the third of the v chord to make it major, giving a half-step gap between the leading note and the tonic.

This is the basis of the harmonic minor scale. The melodic minor pushes this a bit further to sharpen the sixth, getting rid of the large gap between the sixth and seventh.

Then later in the song they play that progression again followed by Eb7 D-7 and Eb7. What's happening there?

That bit goes Em7, Eb7, Dm7, Db7, Cmaj7

What's happening there is you're using the Em7, which was the i, as a ii, setting up another ii-V-i progression. This would normally be Em7-B7-Dm7, but the B7 has been substituted with an Eb7 through what we call tritone substitution. Then when we reach the Dm7, we repeat the process with another tritone substituted ii-V, but this time resolving to Cmaj7.

Here's how I would think of it...

||:Am7 |D7 |Gmaj7 |Cmaj7 |
iv VII III VI
(ii V I in G major)

| F#m7b5 |B7 |Em7 |Em7 :||
iiø V i i

| F#m7b5 |B7b9 |Em7 |Em7 |
iiø V i i

| Am7 |D7 |Gmaj7 |Gmaj7 |
iv VII III III
(ii V I in G major

| F#m7b5 |B7b9 |Em7 Eb7 |Dm7 Db7 |(Cmaj7)
iiø V i bI vii bVII
(ii V i in D minor)
(ii V I in C major)

| Cmaj7 |B7b9 |Em7 |Em7 ||
VI V i i

I found a copy of Autumn Leaves that my bass teacher gave me. It's in the key of G and the chord progression goes
A-7 D7 GMaj7 CMaj7 F#-7b5 B7 E-


Your bass teacher is thinking like a guitar player. They see the opening ii V I IV in G moving to the ii V i in E minor. Then the shedder in them comes out and thinks aw relative major/minor so I can blitz in G major over all of it. Guitar player try to simplify things a bit too much.

What I was taught is beside figuring out how each chord is functioning to outline the key centers a song moves through. Take a few more standards and figure out the chords functions, then draw lines showing the keys centers and where they change that is the info about changing keys you are looking for. Look at the relationship between the keys.

The important thing whether changing keys or not is strong root movement of the chords. If the ear hears a strong root movement it will accept a change of key. Weak root movements are usually chord substitutions or passing chords. All this is about learning what the ear will accept and when they want to hear it.