Thanks for the post! There are indeed a wide assortment of substitutions that can be made, especially in jazz.

There are two factors involved in the concept of chord substitution:

1. Similar notes.
2. Similar function.

Often if two chords have several similar notes they can be sub'd for each other. For example, FMaj7#11 and G7.

FMaj7#11 = F-A-B-E
G7= G-B-D-F

So, they share 2 notes in common. Also, the A note is found in a G9 & that makes it closer.

However, an F maj7 in the key of C functions as a sub-dominant (IV). Whereas a G7 functions as a dominant (V). So, some of this comes down to the personal taste of the player & how much wiggle room you are willing to allow in your substituting! :)

Consider G7 and Bm7b5.

G7= G-B-D-F
Bm7b5 = B-D-F-A

So, these share 3 notes in common. Again, the A note is found in a G9 & that makes it closer.

Moreover, a Bm7b5 in the key of C functions as a dominant (vii). And of course the G7 also functions as dominant (V)!

The G7 and Db7 are quite close too & are very much a cornerstone of chord substitution in jazz, blues & even later classical. It's known as the tritone substitution when the (V) & (bII) both are dominant chords functioning as a (V). I cover it in depth in this lesson.

http://www.guitartricks.com/lesson.php?input=13881
http://www.guitartricks.com/lesson.php?input=16064
http://www.guitartricks.com/lesson.php?input=16065


Thanks for the interesting discussion!