Chamber music is a form of classical music that is composed for a small group of instruments—traditionally a group that could fit in a palace chamber or a large room. Most broadly, it includes any art music that is performed by a small number of performers, with one performer to a part (in contrast to orchestral music, in which each string part is played by a number of performers). However, by convention, it usually does not include solo instrument performances. Because of its intimate nature, chamber music has been described as "the music of friends". For more than 100 years, chamber music was played primarily by amateur musicians in their homes, and even today, when chamber music performance has migrated from the home to the concert hall, many musicians, amateur and professional, still play chamber music for their own pleasure. Playing chamber music requires special skills, both musical and social, that differ from the skills required for playing solo or symphonic works. Johann Wolfgang von Goethe described chamber music (specifically, string quartet music) as "four rational people conversing". This conversational paradigm – which refers to the way one instrument introduces a melody or motif and then other instruments subsequently "respond" with a similar motif – has been a thread woven through the history of chamber music composition from the end of the 18th century to the present. The analogy to conversation recurs in descriptions and analyses of chamber music compositions.