Listen! Coleman Hawkins and Lester Young on "Body and Soul," and you get your eyes tested at no extra charge.

I gather if you're reading this you'd like to be able to play in a jazz group, join a jazz jam, or maybe just bring some new ideas to what you're already doing. In short, you'd like to know "the stuff that jazz players know." How bout I offer up some words of encouragement, using what I call The Eye Test. Ready? First hold your thumb up, level to your eye, at arm's length. Now focus on your thumb. Got it? Now focus on the wall behind your thumb. See the wall become clear, and your thumb go all blurry? Now focus back on your thumb, then the wall again... Do you have any idea how you pulled that off? Your conscious mind gave an order, "I want to see that," and a complex and beautiful dance of tiny muscles ensued, almost entirely free of your supervision. It's the same thing with improvising. Keep your brain fed with musical and fingerboard knowledge, don't forget beauty, give it good directions, then trust that unconscious part to give your playing... well, you. 

Here's another bit of your grey matter you can lean on: the banjo player part. Bluegrass, old time, jazz, R n' B - they're all ponds fed by the same great American river. One may seem a little "deeper," another kind of "swampy," but it's the same water, whichever ones we bathe in. In other words, as a banjo player you probably already know more about jazz than you may think. Trust your experience!

You also probably know that playing over a "jazz tune" involves somehow negotiating a series of "chord changes." Well, yes and no, and yes. And no... Here's why it's not so cut-and-dried: think of a song as being like a building, with a series of structural layers. The top layer is the melody. Below that, the harmony ("the changes"). Next you have the keys implied by various groups of chords. Finally, the foundation - the original key of the tune. So you have 1) a melody, 2) what its chords are, 3) what its chords do, and 4) the "home key." Each layer is affected by the one, or ones, below it, and a player can access any or all of them in the course of a solo.

A musician's preference in this regard can be a hallmark of his or her style. Tenor saxophonist Coleman Hawkins (aka "Bean") could get quite literal about the harmony, as in his famous 1939 solo over Body and Soul. ( http://youtu.be/Sul_9BcgOOI ) On the other hand, the other tenor colossus of Hawkins' era, Lester Young ("Prez") once said it bugged him when he'd be at a jam session and the pianist would be calling out chords to him because "that's not what I hear." Compare Prez' version of the same tune. ( http://youtu.be/tBfqqbm50uw )

Bean is "local," Prez is "express." And as you might have experienced when you're on a train that unexpectedly whizzes by your station, sometimes a route can be a combination of the two.