On Giant Steps and Free Will

If you want to open the black box of free will and see what's inside, improvise over the chord changes of Giant Steps. If using only the chord scales from each of the chords your brain would be so busy attempting to use its own idea of free will, by way of its own understanding of music theory. But since the changes are going by so fast, there's nothing to figure out--and you simply surrender and surf over the top of it. I think most pianists and bassists give up on playing exactly every chord tone, and everything then becomes a “passable” passing tone. The listener has to interpret the piece as a whole, and consequently surrender themselves to it, but the player has to think they have control or achieve some level of it. 

The idea that you'd make something just on the edge of impossibility is where the idea of "spirituality" exists. That's partly where Coltrane's genius comes from, but actually many artists in other domains know this as well. That's just where the "art" is.