E. T. A. Hoffmann wrote in 1813 that instrumental music
is the most romantic of all the arts – one might almost say, the only genuinely romantic one – for its sole subject is the infinite. The lyre of Orpheus opened the portals of Orcus – music discloses to man an unknown realm, a world that has nothing in common with the external sensual world that surrounds him, a world which he leaves behind him all definite feelings to surrender himself to an inexpressible language.
Oliver Strunck, ed. Source Readings in Music History (New York, 1950), pp. 775-76. Cited in : Plantinga, Leon (1984) Romantic Music. New York: Norton, p.14.