The V7 chord is called the “dominant” chord because it drives the music back to it’s foundation. It signals the ear to anticipate that the next chord you hear is the “tonic” chord. That doesn’t always happen, and I will explain why in another session.
Several years ago I was afforded the opportunity to study with Roget Pontbriand, Professor of Jazz Studies at Palm Beach Atlantic University and former trumpeter for Maynard Ferguson’s Big Band. Roget enlightened me to the basic function of scale/chord relationships, and I would like to share a few basic principles from those lessons that apply to V7 chords.
In a nutshell, chords are typically constructed in 3rds up to the 7th degree. In jazz, the upper extensions (9ths, 11ths, and 13ths) of the chords are implied. There are countless books and materials available with many options to explore. I will only describe a few here. If you are just now beginning your journey into jazz, these principles will hopefully simplify things a little. However, it is advisable to understand how all pitches in each scale (the foundation of chords) function even if you don’t use all of them all the time.
1. For all I7, II7, and V7 chords – play the dominant mode of the major scale from its intended tonic chord. This gives you a 9, 11, and 13.
Example: In the key of Eb, Bb7 = Eb Major (‘Bb’ is the 5th mode of the Eb Major scale.)