Before we get tangled up in too many rhetorical flights of improvisational philosophy (that's for next week), let's do something very practical. Let's improvise something.
The project I have in mind is short. It should come in quite handy for church organists and pianists. I'd like to take the tune known as "Old Hundred" which is used as the doxology in many churches (meaning you would play it every week), and create--improvise, an alternate introduction for it.
[here's the score if you need one]
Many organists simply play that last phrase of the hymn to tell the congregation to rise and get ready to sing. We are going to work our way through the whole thing, using this as our plan:
The first phrase will be simply the melody in octaves
The second and third phrases will consist of two-voice counterpoint
The last phrase will be in full chords straight out of the hymnbook
Looking at our overall plan, it is apparent that the only real improvisation that will take place will be in the second and third phrases of the music. By my count, that is 16 melody notes for which you will supply your own created notes--one to "go against" each note of the melody. You will, in other words, only be responsible for the creation of 16 notes. And if even that seems a little too risky, you could always write down what you are creating so that if you have a church job, when the time comes to play it on Sunday, you aren't actually trusting to the inspiration of the moment. As your comfort level increases, though, you might try improvising in the actual service, if not now.
play the melody of the doxology alone. Learn it a phrase at a time, and memorize that melody. You'll want to know the melody well enough that you can spend all your concentration on the duet you will create in the left hand to go with it. If this takes a couple of days, take the time. Internalize it. Memorization is going to turn out to be an important part of improvisation (!) Finally, apply the
"postlude test"--so named because people invariably come up to the organist and try to hold a conversation with him while he is still playing the postlude. If you can play the melody of "Old Hundred" fluidly while holding a conversation, you have definitely got it down!
Now we are going to create some two-voiced counterpoint. The way to do this is to play each melody note in the right hand, and compliment it with a single note in the left hand which sounds pleasant in combination with it. (If you'd like a fancy term for it, this is known as 1st species counterpoint).
Since you are in the key of G major (unless you happen to play the doxology in another key; then substitute that key for G) you will choose notes belonging to that scale, which conveniently happens to be all the white keys save F, which is instead F-sharp. In order to create effective counterpoint, you will want to try other members of the same chord (hint: if you get stuck, playing the soprano and bass voices alone, or the soprano and alto alone, or the soprano and tenor alone, of the written score will sound like what we are trying to achieve here). Generally you will want to avoid playing the same note as the melody, although that can work in a pinch. Even better, you will want to try not simply to satisfy the immediate needs of pretty harmony between each melody note and yours, but try to build a line that, if you played it alone, would itself make a nice melody. It should have some direction and melodic interest. If you can do that, you've really accomplished something! Congratulations!
Of course, that will also get easier to do once you aren't limited to playing a single note of the created accompaniment to a single note of the melody. Although harder to do, perhaps, allowing the created voice to move in eight notes, or even sixteenth notes (2nd or 4th species counterpoint, respectively) will create some really interesting lines, and once you know how to do this (which I understand may take some time) could get rather addictive, and you might find yourself wanting to introduce any number of hymns this way!