Jazz musicians may object to this notion that they are not playing or expressing spontaneous, new melodies when improvising, but I am not saying that they are NOT doing this. I am simply saying that their ability to do this is derived far MORE from PERSPIRATION and far LESS from INSPIRATION than they may want us to believe.
In good improvisation there is definitely an element of playing by ear - being able to play on the instrument ideas that come into your head. However, I would dare say that nearly every idea that comes into your head is something you have either heard or practiced before, so again you are only reorganizing...not inventing.
How does an artist paint? She gets her brushes and oils and a clean canvas, and creates a work that is made from hundreds of strokes that she has learned well through practice.
How does a quarterback make a touchdown pass? He executes a play that has been practiced to near perfection. He certainly doesn't invent a brand new play in the heat of the contest. Is there room for artistry in the execution of the play? Certainly.
How about one more comparison. How does a chef create someone's meal? Typically by following a recipe. However, if he wants to create something new on the spot, he will only use ingredients that he has an intimate knowledge of. Thus, the recipe may be unique, but it is still only a creative combination of available materials.
The way that the artist, quarterback, and chef do their creative work is perfectly and directly comparable to how a jazz musician improvises. A jazz musician simply takes the melodic ideas and patterns that they have learned to sing and/or play and places them in the right key, organizing and connecting them with some degree of artistry.
Charlie Parker practiced the saxophone for 11-15 hours a day for over 3 years in order to become "The Bird". What did he practice? Did he practice making up new melodies all day long? No, he practiced scales and patterns. He practiced his scales until he could play them faster than many thought humanly possible. And he transcribed solos and learned to play his favorite licks (or patterns as I call them) fluently in every key. Armed with these raw materials, he was finally able to stand up and play an incredible solo. And, because he possessed a degree of "inspiration", his "perspiration" not only made him into a great jazz musician, but also allowed him to take jazz into a new direction as a leading figure in the "be-bop" movement.
An internationally acclaimed contemporary jazz saxophonist, Seamus Blake, is a great case study for the typical jazz musician. He says, "I began, as most saxophonists do, by imitating all the great masters. I learned solos by John Coltrane, Sonny Rollins, Dexter Gordon, Joe Hendserson, Charlie Parker, Cannonball Adderley, Ben Webster, and many more. Even today, my sound has varying degrees of influence from all thos players, but earlier on it was much more derivative. Sometimes I would play entire phrases lifted from Parker or Coltrane, but after awhile I began to edit myself." (interview in JAZZed Magazine, November 2011) See? From the very beginning, and even now, the great Seamus Blake is playing stuff that he LEARNED through PRACTICE and through copying the ideas of others. He is organizing, not creating from nothing.
Whenever I hear an amazing young jazz soloist, I inevitably hear from his teacher that she is a great player because she practices 3-4 hours a day. Improvisers are not BORN that way. They are MADE through hours and hours of dedication to mastering scales and patterns.
Certainly, as in athletics, some people are more naturally gifted than others in various ways. However, I firmly believe that ALL students and ALL music educators can learn to improvise, and can improvise well over a few simple chord changes with just dozens (not hundreds) of hours of practice. It can be a delightful journey and a satisfying way to engage with music. It requires a very practical understanding of music theory...more so than is utilized in simply reading and playing written music. It is one of the 9 National Standards all students should experience in their music education. And now, with the Improv Pathways classroom jazz improvisation method, it is very, very achievable.