Odds are you have seen chord names like D major 7th, C minor 9, or A7. These chords all have at least one thing in common, chord extensions. Chord extensions are notes that have been added to basic triad. In this lesson we will go through exactly how chord extensions are made by starting with a C major triad and turning it into a C major 9 chord by adding a couple of chord extensions. If you don’t know how major triad chords are made I suggest you go check out the lesson on Major Guitar Chords before you continue with this lesson. We will be in the key of C major for this lesson. As a reminder, the C major scale is spelled C D E F G A B.
In order to understand exactly how chord extensions are made we will build a C major 9 chord. Start off by playing a C major triad with your 4th finger on the 10th fret of the 4th string, 3rd finger on the 9th fret of the 3rd string, and 2nd finger on the 8th fret of the 2nd string. The notes in a C major chord are C, E, and G. At this point you should understand that major chords are made up of a root, 3rd and 5th. You should also know that the distance between the root and the 3rd of a major chord is a major third and the distance between the 3rd and the 5th is a minor third. If you are clear on these two things that’s great, if not you might want to go back and review some of the music theory lessons on chords.
If you want to put a chord extension on an existing chord, all you need to do is stack another third on top. For example, now that we have built a C major triad all we need to do in order to put a chord extension on it is stack another third on top of the G note. We are going to be making a C major 7th chord so we will need a major third to go on top of the C major triad. A major third away from G is B. Play the C major triad again and add a B note to it on the 7th fret of the 1st string with your 1st finger. This is a C major 7th chord and it is spelled C E G B.
Time to add one more extension to the C major 7th chord in order to make it a C major 9 chord. Stack another third on top of the B note of the C major 7th chord. This note would be a D. From B to D is a minor third. This is exactly what we need to finish off our C major 9 chord. A C major 9 chord from the root up is spelled C E G B D.
Check out the chord diagram we have provided for you. This is a good voicing for a C major 9 chord. You will probably notice that there five notes in a C major 9 chord but there are only 4 notes in this shape. A lot of times the 5th of larger chords is omitted. That is not a big deal. Often you will see that chords with extensions will have a note or two that have been left out.
Building chords with extensions is just a process of stacking major and minor 3rds. You don’t necessarily have to think of this whole example in terms of stacking thirds though. You could think of it in terms of scale degrees as well. If a C major chord is made of the 1st, 3rd, and 5th scale degrees of C major scale, a C major 7th chord would be made of the 1st, 3rd, 5th, and 7th scale degrees, and a C major 9 chord would be made of the 1st, 3rd, 5th, 7th, and 9th scale degrees. Don’t let this trip you up. Just think about extensions in the way makes the most sense to you.
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