We often hear improvisers speak about improvisation as being "spontaneous composition" or as Patrick Moraz puts it, "instant composition." And in many ways, that's true. The process of creation is similar: you open to the musical flow and see where it leads. Part of composition is like slowed-down improvisation. Instead of immediately playing the musical idea, you notate it.
But there's a huge difference between the two that often gets overlooked:
When you're improvising, you don't really edit too much, or at all in some cases. Whatever comes out, comes out. You're just like a train conductor, making sure the train stays on the track and that the music works as a whole. You need to enjoy what's happening and not worry about minor details or mistakes. The overall "flow" is of utmost importance. Sometimes the resulting music will be great and sometimes not. "C'est la vie!"
With composition, you start by improvising (sometimes on an instrument, sometimes in your mind) and see what happens. Sometimes the music comes out perfectly the first time. If this happens, great, you have your composition. But far more often you'll need (want) to go back and see what works and what doesn't:
"This sounds good, but what it I changed these few notes?"
The beginning is interesting, but then it loses energy. What needs to happen at that spot?"
"Maybe the whole thing should really be in G?"
"I like the melody, but the chords don't seem to do it justice."
In short, this is the craft of musical composition. In the words of Marian the Librarian, this is what made Shakespeare and Beethoven great. It wasn't the "dum-dum-dum-dum," but how the rest of the piece unfolded after that initial burst of energy.
There's a lot of boring music out there, in all genres. There are some incredibly famous composers of all types of music who are in great need of an editor; either an "internal editor" or a trusted friend who will tell them when their new "masterpiece" needs to be reworked or tossed into the trash bin.
Adele knows this. Take her song "Hello." Great song, right? Well, it almost wasn't! Adele says that after she wrote the songs for her album "25," her trusted friend Rick Rubin bluntly told her they were no good. So, as she says, she "went back to the drawing board. Worked my arse off."
How many of us are willing to do the same?
The real difference between improvisation and composition isn't so much about the beginning process. That's about opening to the flow. It's about what happens after that. With improvisation, you play what comes out and enjoy what happens. With composition, you might begin like this but then you need to shape the resulting music, much like a potter shapes a lump of clay. Shape it, finesse it, and at times don't hesitate to throw the whole thing out and start anew.
At a certain point, one of two things will happen: 1. Your piece will be perfect, or 2. Your piece won't be quite perfect but you'll need to accept it as it is and start composing your next piece.
Improvisation and composition. Similar, yet different. Explore both for a full musical life.