The fantasy as a genre is characterized by its fluidity. It sounds like an improvisation, but fantasies such as the four treated here have been notated by their creators and thus preserved, fixed in their gestalt – robbed of the absolute freedom of true improvisations. Unlike forms that are more carefully circumscribed through historical practice and also theoretically, the fantasy, chameleon-like, changes its shape and color in the hands of different composers. This project will compare the fantasies of four great masters from four different epochs of music history. Characterized as “formless,” the fantasy is revealed in the comparison to possess a versatility that allows it to permeate other genres easily such as the sonata. The problem of the apparent contradiction between a “written improvisation” and a fixed form is solved in four different ways by these composers: J.S. Bach, Mozart, Chopin, and Scriabin.