The development and impact of program music in the Romantic period is actually quite interesting. Program music is instrumental music (generally orchestral in nature) that tells a story and has a strong literary connection. Let's take a closer look at some of the specific forms of program music and the music's development during the 19th century.
Incidental music is music that was to be inserted between the acts of a play originally. The most famous example of incidental music is Mendelssohn's A Midsummer Night's Dream. Its connection to Shakespeare's play of the same title is evident. At this early stage of program music, the composition was inseparable from the influencing literature as both the musical work and the literary work were performed together.
Moving ahead historically, we come to the works of Franz Liszt. Liszt brings the tone poem and the symphonic poem. The tone poem is a single-movement orchestral work that has a literary connection and tells a story; the symphonic poem is essentially the same thing except that it has multiple movements. Some of Liszt's tone poems include Don Quixote and Don Juan. It is interesting to note that Liszt's program pieces are no longer performed in conjunction with their inspirations. The assumption is that the audience is familiar with the story of these great works of literature.
The symphonic poem is extremely similar to the program symphony. The differences are so particular that we will consider them as the same thing for the purpose of this introductory discussion. The most famous example of a program symphony - and probably of program music period - is Hector Berlioz's Symphonie Fantastique. This monumental composition is interesting for two reasons. First, Berlioz produces his own literary inspiration for this work. The writing is the result of his opium-induced dreams and his infatuation with the actress Harriet Smithson. Since the audience will not be familiar with Berlioz's storyline, program notes are provided at each performance and serve as an explanation of the piece.
The second important aspect of the Symphonie Fantastique is the development of the idee fixe. This recurring musical theme will assist in developing the composition's story and will later serve as the impetus for Wagner's development of the leitmotif and its use in his musik drama, The Ring of the Neibelung.
Finally, our journey takes us to Czechoslovakia and the music of Bedrich Smetana. Smetana's symphonic poem Ma Vlast includes the world-renown composition The Moldau. Inspired by the geography of the Czech countryside, The Moldau is program music in variation. While no single literary work is alluded to as Smetana's inspiration, much of the native folklore is set on the river's banks. Smetana's composition allows program music to include inspiration from natural settings in addition to literary works.