Substituting Two Ahead
The easiest form of chord substitution is to use triads or 7th chords from within the same key as the original chord. In any key you can always substitute the chord two degrees ahead in the scale, thus creating a higher extension of the chord. E.g. Here are the scale tone triads in the key of C major.
Notice that an E minor triad contains the notes E, G and B. A Cmaj7 chord contains the notes C, E, G and B. Therefore, a Cmaj7 chord can be implied by playing an E minor arpeggio over a C chord. Since the bass or the keyboard is almost certain to be playing the root note, the E minor chord makes up the remainder of the Cmaj7 chord. Scale tone 7ths can be implied for all of these triads by substituting the chord two ahead in this manner. E.g. an F triad can be substituted for a Dm triad, thus creating a Dm7 chord, etc.
Listen to the following example which contains triads two ahead being substituted for the original triad, thus creating scale tone 7ths on every chord. The chord symbols show the triad being played and then a forward slash (/) followed by the bass note which is being played under the triad. Chords notated in this way are called slash chords. This is a specific way of indicating the substitution being used (e.g. Em/C is the same as Cmaj7)
The process of substituting chords two degrees ahead can be continued further by substituting two more ahead and two more ahead until you have covered all the degrees right up to the 13th of the chord. E.g. if you go two degrees further up the scale from E minor, you come to a G triad. It’s notes are G, B and D. These are the same as the 5th, 7th and 9th degrees of a Cmaj9 chord. This means you can play a G triad over a C bass and give the impression of a Cmaj 9 chord. Playing an A minor triad over a D bass gives the impression of a Dm9 chord because the notes of the An chord (A, C and E) are the 5th, 7th and 9th degrees of a Dm9 chord. This process applies to all chords within a key as shown in the following example which implies 9th chords for every degree of the scale.
The reason this kind of substitution works is that the roots of the chords to be substituted go up by 3rd intervals – the same intervals used to create scale tone chords in the first place. The following example shows a Cmaj13 chord broken up into five different triads: C, Em, G, Bdim and Dm. Each of these triads is two degrees ahead of the previous one in the C major scale. Memorize the exercise and then repeat it on all twelve notes of the chromatic scale, mentally naming the degrees and then the actual notes as you play.
By starting on the second degree of the scale, you can create chords up to a min13th by substituting two ahead. This is demonstrated in the following example which shows a Dm13 arpeggio made up of Dm, F, Am, C and Em triads.
By starting on the fifth degree of the scale, you can create chords up to a 13th by substituting two ahead. This is demonstrated in the following example which shows a G13 arpeggio made up of G, Bdim, Dm, F and Am triads.
