Triads are obviously not the only chords, there is also something called extensions. Extensions are notes extended, or added beyond the seventh. This means you can have a major triad with a seventh, and it would be renamed to a major seventh chord. A minor triad have may also have a 9th, turning it into a minor 9 chord. This is why jazz guitar chords may seem overwhelming, but they are just extensions, and that’s what we’re going to cover in this lesson.
So let’s talk about seventh chords. Maybe your in the situation where you see a seventh chord. They are very present in jazz sheet music. You’re going to want to be able to play multiple genres as a guitar player, but to do so, you need to know multiple chords.
Seventh chords are just triads with a seventh. A dominant seventh chord involves a major triad with a flat seven. The next chord after that is a major seventh chord, which has a seventh, other than a flat seven. If you want a minor seventh chord, you’re going to need a root, minor third, fifth, and seventh. You pretty much get the idea, just add a seventh to any triad and turn it into a seventh chord. Here’s a chord chart with a few seventh chords.
This is just the beginning, there are still plenty of extensions you can add. You can add more than one extension by the way. You can probably imagine the possibilities are basically endless.
Guitar: A Divergent Path 