 For composers, the sonata form is like the plot of a play or movie script, describing when the crucial plot points are, and the kinds of material that should be used to connect them into a coherent and orderly whole.At different times the sonata form has been taken to be quite rigid, and at other times a freer interpretation has been considered permissible.In the theory of sonata form it is often asserted that other movements stand in relation to the sonata-allegro form, either, per Charles Rosen that they are really "sonata forms", plural—or as Edward T. Cone asserts, that the sonata-allegro is the ideal to which other movement structures "aspire".