In our inaugural issue of MandolinSessions.com, Understanding the 'ii V7 I' Progression, we brought up the concept of harmonic function. "Drama; it's always about conflict and resolution," was the way this started. The "drama" of a V7 chord, resolved or unresolved is what defines the majority of Western European music, classical, folk, pop. It wasn't until the middle 20th century that these sounds were thrown out the window in contemporary musical styles of atonal and 12-tone compositional techniques.

An unresolved Dominant Seventh chord stirs motion. Roll out a huge arpeggiated G7 on a grand piano and sing "Happy..." and who can resist following up with a tonic C based "Birthday to you!" It's a primordial a 'V7 to I' as you can get.

Music theorists will teach you that in our tonal universe, we have three functions; Home (I) or Tonic, Dominant (V7), and Dominant Preparation (ii, IV, vi and variations on them). When we think C7, in context, more often than not, it will be a V7 or Dominant chord of F. In jazz contexts more often than not, you'll see stylistic interpretations, "spice" if you will that take a basic 7th chord C7 (C E G Bb), include variations like C9 (adding the 9th or D), C13 (adding the 13th or A), and C7 b13 (adding the lowered 13th, the same as a raised 5th or Augmented chord), and use them interchangeably.

If a jazz musician sees or hears C7 in the score, he/she is not thinking C E G Bb, rather thinking a contextual function of "Dominant." That's why depending on what other musicians are doing at the time, chord extensions are not only okay, they are encouraged. All the preceding variations are fair game, as long as the additional chord extensions don't conflict with the melody or another comping instrument. (You don't want to play a C7b9 if someone else is playing a C9.)
It all boils down to function. A good skill to have is to be able to recognize all the 'V7 I' pairs in the Circle of Fifths. Playing through these in all 12 keys until they become automatic is a healthy exercise to add to your practice routine, both physically and intellectually.

Posted by Ted at May 1, 2008 12:49 PM