Analyzing Chord Progressions

I hope everyone had a great holiday. Mine was insane, regular posting will resume as of today, with another post about chord substitution, this should be the last one for awhile.

This time I'm going to take the opposite approach I took in my blues discussion, and take a previously written song and pick apart the chords involved.

I'm going to use Gershwin's “summertime” here, this tune has been done by a pile of Jazz Musicians, this version is in the key of A minor.

Am     |Bb7    |Am   E7|Am   A7|

Dm7    |F7     |F#m7 B7|E7     |

Am     |Bb7    |Am     |G7     |

C    Am|B7   E7|Am     |Bm7  E7|

First we're going to go through and name all the diatonic chords – that is chords that fall within the harmonized scale.

A quick note, all chord symbols will be written with upper case roman numerals, and the chord qualities will be shown, the reasoning for this is because in more complex progressions, and minor keys, it becomes more and more bizarre to use uppercase for major and lower case for minor – I'm also going to relate the chords back to the A major scale, this is so that we don't get caught up in which minor scale we're using, since none of them are more important then any others.

Im              Im   V7 Im
Am     |Bb7    |Am   E7|Am   A7|

Vmim7                    V7
Dm7    |F7     |F#m7 B7|E7     |

Im              Im  
Am     |Bb7    |Am     |G7     |

bIII Im      V7 Im      IIm7 V7
C    Am|B7   E7|Am     |Bm7  E7:||

Now let's go through it again and analyze for secondary dominance.

Im              Im   V7 Im   V7/IV
Am     |Bb7    |Am   E7|Am   A7|

VIm7          IIm7/V V7/V V7
Dm7    |F7     |F#m7 B7|E7     |

Im              Im      V7/bIII
Am     |Bb7    |Am     |G7     |

bIII Im V7/V V7 Im      IIm7 V7
C    Am|B7   E7|Am     |Bm7  E7:||

Now let's find the tritone subs, an easy way to look for these is to find dominate 7 chords not yet analyzed with the next root a semi-tone away.

Im      subV7   Im   V7 Im   V7/IV
Am     |Bb7    |Am   E7|Am   A7|

VIm7   subV7/V  IIm7/V V7/V V7
Dm7    |F7     |F#m7 B7|E7     |

Im      subV7   Im      V7/bIII
Am     |Bb7    |Am     |G7     |

bIII Im V7/V V7 Im      IIm7 V7
C    Am|B7   E7|Am     |Bm7  E7:||

The reason it's subV7/VI and not subV7/II/V/V, is simply because the latter is incredibly difficult to read, avoid multiple /s whenever possible.

This is also a delayed resolution - meaning it doesn't resolve to where it should (E7) right away, it has some other chords before.

And there you have it, using that method you can pick apart almost all if not all chord progressions you've heard. There's some stuff I haven't gotten into here, but those are LONG explanations.