Questions about the ontology of music tend to be addressed formally under the banner of philosophy, as the long bibliography on that topic attests.1 But ontological debates arise frequently and intensely in other informal contexts. For instance, if I were to ask someone waiting in line to hear a performance of Götterdämmerung at Bayreuth if David Ocker’s 7-minute digital rendition of Wagner’s Ring Cycle is a performance of that four-opera work, the answer would most certainly engage issues of musical ontology.2 Such ontological debates operate not only in classical but also in jazz and popular domains. For instance, the responses on YouTube to the posting of John Oswald’s ‘Dab’, a sample-based collage of Michael Jackson’s ‘Bad’, range from ‘horrible’ to ‘amazing’.3 Not far from the surface of these disparate responses is the ontological question: What is music? Another anecdote from my own teaching experience raises yet another dimension to issues of musical ontology. I often teach music of the 1950s and 1960s to undergraduate nonmajors, and typically my syllabus includes John Cage’s 4′33" and Elliott Carter’s Double Concerto for Harpsichord and Piano.4 Students tend to be mildly amused by Cage’s work, especially when they listen to a recorded performance by Frank Zappa, but Carter’s Double Concerto often outrages them.5 The outrage arises both from their personal sense of musical propriety (typically but not always: it should be tonal, have a backbeat, and last about 4 minutes) and from their realisation that a cultural economy exists that provides monetary compensation to Carter. These differing kinds of responses engage some fundamental questions about musical ontology. On one hand, Cage did not intend any particular sounding occurrences in 4′33". Rather, his intention is to delimit a temporal span of silence during which listeners may or may not choose to hear ambient sounds as music. For my students, this lack of intention for the work’s particular sound seems to absolve Cage from responsibility, and their response seems to be: as a musical work, 4′33" is playful experiment about listener response. But the reaction of outrage to Carter’s Double Concerto entails recognition of Carter’s intention – his sound design is deliberate. My students’ reaction requires acknowledgement both of an aesthetic world that differs radically from the one they inhabit and of an aesthetic economy that rewards composers such as Carter. This two-faceted acknowledgement may or may not re-shape students’ aesthetic tastes, but it does illuminate ontological difference.