Philly, I'm glad you mentioned Jazz.....I have been playing Piano/Keyboards off and on most of my life. Within the past 10 years I have had fun learning Guitar, Ukulele and Steel Guitar. Yes, Indeed I love music. Just lately I've become interested in playing Jazz on my Ukulele......I love the Uke Philly because there are only 4 strings and mine is tuned to GCEA so that when played with no fretted strings I'm playing a C6...Well, let me cut to the chase, this guy is teaching Jazz Uke on line and he really is good. I'm having a hard time trying to understand some of his substitutions. For example, as you prob. well, I'm sure you know Lots & Lots of R&R from the '50's use I vi ii V progression......SO, he says we will substitute other chords for the progression....but one of those substitutions I cannot figure out...For example in the key of C he says substitute the vi (in this case Am) with C#dim....It doesn't seem there are enough notes common to those two chords for a good substitution BUT.......It sounds good when I use but I don't know WHY IT FITS!!! Would you ever substitute an Am for a C#dim?? Can you explain why it works.