I had a right side stroke as a kid; so I'm always looking for substitutions and other tricks to improve my sound. Real amaetur though I am. I've studied the table 0f usual root progressions and substitutions: but where can I find a site or book to tell me about four of the four and other such subs?

Tritone subs are used more commonly than the four of the four (which would be known as an extended dominant. A tritone sub is when you substitute a dominant 7th chord with another dominant 7th chord built on a root a diminished 5th (known as a tritone) away. The 3rd and the 7th tones of one chord become the 7th and 3rd of the substitution chord.

There are good jazz theory books out there, many of which discuss tritone subs. From a bass players perspective, both my "Total Jazz Bassist" book and my "Complete Electric Bass Method (Mastering)" book discuss this subject.

-Dave

Tritone subs are usually done with dominants (V chords), not sub dominants (IV chords).
Let's you have this (simple) E major progression
E major, B dom, Emajor
I________V_____I


Now if you move the V chord a tritone away this becomes
E major, F dom, Emajor

Forgive me if my response was too general for some, but sometimes I respond to these just before I head out for a gig! I was simply stating that the IV of a IV isn't really a substitution of use as is the tritone sub. He asked for a resource for substitutions and I proposed the tritone sub as a commonly used sub used in jazz harmony and even other genres. I didn't outline the specifics because the question was about a resource for information, hence why I recited the titles of a couple of books which show them in the context of tunes. However, I assumed that someone could understand the direction I was going with the response. Thanks for scratching the surface of the tritone sub question. My response does state that a tritone sub is dominant chords. But in any case, I hope you use these subs in tunes from blues, to Autumn Leaves to Donna Lee to Giant Steps and your own compositionsSubs. Have fun.

Dave