Impressionism, Symbolism, Expressionism

Impressionism
Musical Impressionism was based in France, and the French composers Claude Debussy and Maurice Ravel are generally considered to be the two "great" Impressionists. However, composers are generally not as accurately described by the term Impressionism as painters in the genre are. Debussy renounced it, saying "I am trying to do 'something different'- in a way realities- what the imbeciles call impressionism is a term which is as poorly used as possible, particularly by art critics."Maurice Ravel composed many other pieces that aren't identified as Impressionist. Nonetheless, the term is widely used today to describe classical music seen as a reaction to 19th century Romanticism.

Accordingly, many musical instructions in "impressionist" pieces contain musical instructions written in French.

Other impressionist composers include Karol Szymanowski (Polish), Charles Griffes (American), Paul Dukas (French), and Ralph Vaughan Williams (English).

Symbolism was a late nineteenth century art movement of French and Belgian origin in poetry and other arts.

Many Symbolist writers and critics were early enthusiasts for the music of Richard Wagner, a fellow student of Schopenhauer.

The Symbolist aesthetic had a deep impact on the works of Claude Debussy. His choices of libretti, texts, and themes come almost exclusively from the Symbolist canon: in particular, compositions such as his settings of Cinq poèmes de Baudelaire, various art songs on poems by Verlaine, the opera Pelléas et Mélisande with a libretto by Maurice Maeterlinck, and his unfinished sketches that illustrate two Poe stories, The Devil in the Belfry and The Fall of the House of Usher, all indicate that Debussy was profoundly influenced by Symbolist themes and tastes. His best known work, the Prélude à l'après-midi d'un faune, was inspired by a poem by Mallarmé, L'après-midi d'un faune

Aleksandr Scriabin's compositions are also influenced by the Symbolist aesthetic. Arnold Schoenberg's Pierrot Lunaire takes its text from German translations of the Symbolist poems by Albert Giraud, showing a link between German expressionism and Symbolism.

Expressionism
Much like impressionism, expressionism is a term that was first used in connection with painting. In many aspects, it is the direct opposite of impressionism. Unlike impressionism, its goals were not to create passive impressions and moods, but to strongly express (hence the name) intense feelings and emotions.
Expression puts the emotional expression above everything else. While romantics (such as Robert Schumann or Johannes Brahms) also showed emotion in their music, they did so while still following traditional methods of writing music. On the other side, expressionists completely ignored tradition and focused on expressing emotions at all costs. For this reason, expressionistic music is often dissonant, fragmented, and densely written.
To put it another way, let's compare it once more to impressionism. You could say that an impressionist work portrays what is in the world around the composer: it creates an impression of what is being seen. An expressionist work, on the other hand, portrays what is going on inside the composer's mind: it is an expression of what is being felt. Three major expressionist composers are Schöenberg, Alban Berg, and Paul Hindemith.