What are the three characteristics of impressionist music?

The Impressionist period was from about 1860 to the early 1900s. Two famous composers were Debussy and Satie. The music is all about giving and IMPRESSION of an image or feeling. Nothing is clear cut, it's slightly 'fuzzy' like the impressionist paintings by Monet or Van Gogh.

Modes were commonly used rather than the traditional diatonic scales. The whole-tone or pentatonic scales were also used. 7th chords were very common, with parallel chords adding to the impressionist style. You can also use 9ths, 11ths, and 13ths.

Many pieces feature a dreamy mood which are helped by treble and the bass fitting together but not in a traditional way. The almost sound 'wrong' to the untrained ear, but it actually works. A good example of this is 'Claire de Lune' by Gabriel Fauré which I have actually performed (a beautiful piece).