https://ericbarnhill.wordpress.com/facts-about-improvisation/
I just came across this old yet interesting article about the improvisation stories of certain classical composers. Since classical improvisation back then was a huge common practice and needed to be taught, how did classical composers such as Bach, Mozart, Beethoven, Chopin, Liszt, Debussy exactly practice piano improvisation? How are they so good at making melodies out of thin air?