 The main problem with the first kind of condition is that every sound seems capable of being included in a musical performance, and thus characterizing the essentially musical features of sounds seems hopeless. (We need only consider the variety of “untuned” percussion available to a conservative symphonist, though we could also consider examples of wind machines, typewriters, and toilets, in Ralph Vaughan Williams’s Sinfonia Antartica, Leroy Anderson’s The Typewriter, and Yoko Ono’s “Toilet Piece/Unknown”.) Defenders of such a condition have turned to sophisticated intentional or subjective theories of tonality in order to overcome this problem. If the essentially musical features of a sound are not intrinsic to it, but somehow related to how it is produced or received, we can classify just one of two “indiscernible” sounds as music. The details of one’s theory of essentially musical features will determine how much avant-garde “sound art” counts as music.