A product of the romantic school is called "programme music." This means music which is intended to illustrate a definite story, and its best examples are those which endeavor to illustrate wholly by voicing in music the sequence of emotions contained in the tale, with the aid of such descriptive music as will convey some idea of the scenic surroundings. The reader will readily understand that some acquaintance with the composer's purpose is necessary to an appreciation of such music. A key to the plan is offered usually by the title. A composition labelled "Macbeth" would, of course, be understood as intended to illustrate Shakespeare's tragedy, and the hearer would naturally call to his aid in listening to it his knowledge of the drama. Two familiar forms of programme music have grown out of the attempts of the romanticists. One of these is the symphonic poem, and the other the programme overture. The symphonic poem is a composition symphonic in style and general treatment, but shorter than a symphony and without pauses between its movements and designed to illustrate a story. An attentive listener will find that a symphonic poem contains definite principal themes, development or working out, climaxes, and conclusion, for no matter what the sequence of emotions in the story may be, the fundamental laws of musical form must be observed. The programme overture is an overture built on lines much the same as those of a symphonic poem, but designed as a musical prelude to a play, or a poem of dramatic contents, as, for example Tschaikowsky's "Hamlet" overture, or Goldmark's "Sakuntala" overture. The latter belongs to a poem. In addition to these forms the romanticists have made certain alterations in the old sonata form. One of Schumann's symphonies, that in D minor, is in the usual four movements, but without any pauses between them, and the principal subjects of the work are heard in various forms in the various movements. This plan was followed by Liszt in his piano concertos, which are played without pauses and have their several movements largely developed from the themes announced at the beginning of the works.