Classical music is also different from jazz because true jazz is improvised. However, the differences are not always obvious. Classical music has often been inspired by jazz, and jazz by classical music. George Gershwin wrote music which is both jazz and classical. Classical music, too, can be improvised. The great composers Bach, Mozart and Beethoven often improvised long pieces of music on the organ, harpsichord or piano. Sometimes they wrote these improvistions down. They were, in effect, compositions which were composed in one go.